Atmospheric water capture devices and systems and methods of use thereof

Abstract

The present disclosure provides an atmospheric water capture device for converting water vapor to liquid water. The device may include a housing and a basin disposed within the housing. The housing may include an inlet configured to receive an ambient atmosphere. The basin may include a first section, at least one channel, and a second section. The first section may be configured to draw water away from the received ambient atmosphere. The at least one channel may be configured to store an ionic solution and the water drawn away by the first membrane. The second section may be configured to vaporize water stored in the at least one channel. The invention also discloses a method for capturing atmospheric water by using the atmospheric water capturing device.

Description

[0001] Cross - reference to related applications

[0002] This application claims the benefit and priority of the filing date of U.S. Provisional Application No. 63 / 420,288, filed Oct. 28, 2022, the entire disclosure of which is hereby incorporated herein by reference. TECHNICAL FIELD

[0003] The present disclosure relates to devices for capturing water vapor from ambient air and converting the water vapor into a liquid form. BACKGROUND ART

[0004] Parts of the world are experiencing low water levels. For example, the southwestern United States is experiencing its lowest water levels in 1,200 years. Atmospheric water collection, in which water vapor from ambient air is converted into a liquid form, can be used to compensate for low water levels. Globally, solar-powered atmospheric water collection has the potential to provide water to approximately one billion people. Although water vapor can be used, the water capture rate has not been shown to be close to the solar or thermodynamic capacity of water capture, indicating that there are transport limitation problems that limit the potential capture rate. Here, transport can refer to the movement of water, energy, and chemicals through various media. Existing atmospheric water capture methods rely on a single adsorbent material that performs multiple functions of water capture and / or collection sequentially. Because the functions are performed sequentially rather than simultaneously, the capture and / or collection rate is delayed. Clearly, atmospheric water capture and / or collection can be improved to increase the capture and / or collection rate. SUMMARY OF THE INVENTION

[0005] In various aspects, an atmospheric water capture device for converting water vapor into liquid water is disclosed herein. The device can include a housing and a basin disposed within the housing. The housing can include an inlet configured to receive ambient atmosphere. The basin can include a first section, at least one channel, and a second section. The first section can be configured to draw water from the received ambient atmosphere. The at least one channel can be configured to store an ionic solution and the water drawn by the first section. The second section can be configured to evaporate the water stored in the at least one channel. A method of capturing atmospheric water using the atmospheric capture device is also disclosed. BRIEF DESCRIPTION OF THE DRAWINGS

[0006] Figure 1 is a drawing of a cross-section of an exemplary atmospheric water capture device as disclosed herein.

[0007] Figure 2 is Figure 1 a graph of a thermodynamic analysis of the exemplary atmospheric water capture device.

[0008] Figure 3Illustration of an exemplary solar-powered atmospheric water capture device in the desert.

[0009] Figure 4 Illustration of the performance targets of an exemplary atmospheric water capture device compared to existing atmospheric water capture methods.

[0010] Figure 5 a is an illustration of an example natural model for water capture and evaporation. Figure 5 b is an illustration showing the manner of gel capture and evaporation in an exemplary atmospheric water capture device inspired by natural membranes.

[0011] Figure 6 Illustration of an example custom environmental chamber for characterizing the transport process and 3D geometry of a hydrogel sample.

[0012] Figure 7 It is a graph showing the inverse trend between stiffness and permeability as the crosslinker ratio of a synthetic hydrogel sample changes.

[0013] Figure 8 a and Figure 8 b are photos of a preliminary prototype of a water capture setup.

[0014] Figure 9 It is a graph depicting the historically low water levels in Lake Mead.

[0015] Figure 10 a is an illustration of the average daily rainfall in the United States. Figure 10 b shows theoretical ideal water capture. Figure 10 c shows possible water capture.

[0016] Figure 11 a is a graph showing that existing atmospheric water capture methods cannot capture water at a rate or humidity that would affect dry communities and reach the maximum solar limit. Figure 11 b is a graph showing that the preliminary proof of work of the prototype of the atmospheric water capture device disclosed herein demonstrated capture at a minimum humidity of 10% RH.

[0017] Figure 12 Illustration showing that existing methods using solid adsorbents that are filled at night and release water during the day miss capture opportunities during the day.

[0018] Figure 13 a is an illustration of an example natural model for water capture and evaporation. Figure 13 b is an illustration showing the manner of gel capture and evaporation in an exemplary atmospheric water capture device inspired by natural membranes. Figure 13 c shows that at night, water is captured through the gel and stored in a basin filled with an ionic solution. Figure 13d shows that during the day, the captured water is distilled through the evaporator gel by solar heating.

[0019] Figure 14 is a diagram showing the atmospheric water capture method as disclosed herein.

[0020] Figure 15 a and Figure 15 b are graphs showing the chemical potential at the capture gel (C), basin (B), and evaporator gel (E), and the captured liquid state (H). Figure 15 b shows that a saturated ionic solution (e.g., LiBr) can lower the chemical potential of water and raise its boiling point.

[0021] Figure 16 shows an example hydrogel, where the hydrogel is a network of polymer chains with pore sizes equivalent to the average spacing ξ between the chains.

[0022] Figure 17 a to Figure 17 c show the results of a simplified multi - physics finite element method (FEM) simulation. Figure 17 a shows an ion concentration map, which shows that more salt is distributed at the evaporator. Figure 17 b shows a temperature map, which shows that the temperature in the capture gel increases slightly (due to exothermic condensation) and the temperature at the evaporator rises due to solar irradiation. Figure 17 c shows a gel strain map, which shows that the accumulation of water causes positive strain (swelling) at the capture gel and the release of water causes negative strain (shrinkage) at the evaporator.

[0023] Figure 18 shows a custom environmental chamber that enables the characterization of the heat transfer and 3D geometry of the hydrogel film.

[0024] Figure 19 shows a photograph of the preliminary observation of dropwise condensation on a prototype capture gel - an unexplored ion - and hydrogel - mediated vapor condensation mechanism.

[0025] Figure 20 a and Figure 20 b show the mechanical and permeability test setups suitable for hydrogel characterization. Figure 20 c is a graph showing the observed inverse trend between stiffness and permeability with the change in the cross - linker ratio of a unique hydrogel formulation of polyacrylamide (PNI - co - AAm) copolymerized with N - isopropylacrylamide.

[0026] Figure 21 shows a graph of the preliminary modeling of the condensation rate, evaporation rate, and net water flux for a typical day in July in Las Vegas considering temperature, humidity, and solar radiation.

[0027] Figure 22 a and Figure 22 b are photos of a preliminary prototype of a water capture setup.

[0028] Figure 23 Table 1 is shown: the expected transport processes around the gel and their comparison quantified by dimensionless numbers.

[0029] Figure 24 Conventional ways of conditioning air within an aircraft environmental control system (ECS) are shown, including an air - water separator as a physical device for removing moisture from incoming air. Figure 24 The proposed solution is further shown, utilizing the high surface area, fin - like structure of the hydrogel to effectively capture moisture, dehumidify, and control temperature within a small footprint.

[0030] Figure 25 The humidity - dependent dew point (red curve) for determining whether moisture forms on a surface is shown. As long as any surface inside the aircraft remains above the dew point, no moisture can form via condensation. Here, the air (dry - bulb) temperature is 25 °C.

[0031] Figure 26 The ideal air conditions (temperature and relative humidity) defined by the criteria listed in Table 2 are shown.

[0032] Figures 27A to 27C An overview of the ECS system is shown. Due to its multifunctional nature, the proposed gel - based system has a smaller footprint.

[0033] Figures 28A to 28B A liquid desiccant ( Figure 28A and Figure 28B humidifier) used as a dehumidifier is shown. This two - way phenomenon provides natural, autonomous multifunctional behavior for self - regulation of humidity. When the relative humidity of water vapor is higher than the equilibrium relative humidity of the solution (vapor chemical potential is higher than liquid chemical potential), water vapor can condense into the salt solution. In the opposite case, liquid water can evaporate. Here, the liquid is a saturated sodium bromide solution at 60% equilibrium humidity.

[0034] Figure 29 A saturated potassium acetate solution (red curve) is shown as a potential candidate for a liquid desiccant that can condition air to the ideal air conditions.

[0035] Figures 30A to 30B A comparison between a typical liquid desiccant system for dehumidification and the disclosed system is shown. In the system shown, the hydrogel is used as a solid desiccant and allows the background liquid desiccant to perform the following two functions: (1) provide a chemical potential reservoir for dehumidification ( Figure 30A ) and (2) provide cooling ( Figure 30B)。In a typical system, the liquid desiccant must be sprayed through a complex heat exchanger design that allows water to flow for cooling and allows air to flow through it. Typical designs depend on the direction of gravity, while the disclosed approach is independent of the direction of gravity.

[0036] Figure 31 Shows the results of dehumidification through LiCl ion gels, which indicate an increase in captured water

[0037] Figures 32A to 32C Shows the proposed ion gel condenser concept with spherical geometry for dehumidification. Figure 32A Shows that the salt solution allows water to condense from the environment. Figure 32B Shows the ion gel attached to the substrate through a column with embedded flow channels. Figure 32C Shows the ion gel swelling at higher humidity, and the water captured from the humid air is osmosis-driven into the solution.

[0038] Figure 33 Shows the preliminary results of 2D FEM simulations of ion gel spheres at different relative humidities (RH) and different relative permeabilities quantified by the dimensionless group Π (Equation 9). Below 50% equilibrium RH, the gel shrinks from its equilibrium state (s < 0), and water evaporates from the gel, thus humidifying the air. Above equilibrium RH, the gel swells (s > 0), and water condenses into the gel, thus dehumidifying the air.

[0039] Figure 34 Shows an overview of the preliminary work using gels. (a) Gels and ion gels are synthesized, and several material properties can be tuned. The developed functions allow the use of customized imaging and image processing routines to characterize (b) the mechanical stiffness of indentation tests, (c) the water uptake rate at different humidities, and (d) the wetting contact angle.

[0040] Figure 35 Shows an overview of the multi-physics FEM simulation process that can be executed to solve the transport within the gel.

[0041] Figure 36 Shows a demonstration of the concept of an array of extruded gel spheres through a polymer substrate.

[0042] Figure 37Diagram showing a bio-inspired collection concept. (a) None of the current state-of-the-art research or commercial devices of existing solar-based AWHs meet the performance required to provide safely managed drinking water to 1 billion people as modeled by Lord et al. (green line; Equation 11, Example 4). (b) Current (first-generation) AWH devices use a single monolithic material that can only capture / store or release water at a time. To improve AWH performance, it is envisioned that (c) second-generation and (d) third-generation AWH devices can utilize a separated multi-material architecture inspired by (e) tree frogs and Tillandsia “air plants”. Here, a hydrogel membrane was developed for continuous and rapid capture into a liquid desiccant storage medium ((c) and (d) bottom) – using convective resistance in the ambient air ( R 蒸气) , permeation resistance ( R 凝胶) and convective resistance in the liquid solution ( R 溶液) Similar (f) loops to model the heat transfer process. Coupling capture / storage with solar-powered release (such as (c) a single-stage distillation process or (d) a thermodynamically limited distillation device) constitutes a complete AWH system, where the collection rate is the minimum of the capture rate and the release rate. As some second-generation approaches are approaching the solar limit, the disclosed rapid capture / storage approach is an important part of enabling solar-limited AWH.

[0043] Figure 38 Schematic showing laboratory-controlled water capture tests confirming near-convection-limited performance. (a) Indoor capture test protocol. First, dry air is humidified to the desired RH level using PID control. The humid air with 10% to 60% RH flows into a 3D-printed wind tunnel located below the gel membrane, which is in contact with the liquid desiccant solution above it. (b) Shows the distinct volume change of the solution at a steady rate (57%, 0.9 m s -1 , 75 min) (supplementary video). (c) In 12 separate indoor vapor capture tests with varying humidity and wind speed, all data points collapse along the predicted capture rate (dashed line) within the uncertainty of the velocity (±0.07 m s -1 (1SD); translucent region). Error bars represent 1SD. The results confirm that the water capture and storage system operates with convection-limited behavior and the heat transfer resistance through the gel is negligible.

[0044] Figure 39Outdoor water capture tests demonstrate high water capture in Las Vegas, the driest city in the United States. (a) In late November 2022, outdoor capture tests using a 50 mm diameter fan produced (b) 5.50 kg of water over a 24-hour period. m-2 d -1 . Relying only on natural wind without a fan produced 1.99 kg m -2 d -1 . Over the entire test period, temperature and humidity varied as shown in (c) and (d).

[0045] Figure 40 Shows the global impact of convective-limited water capture. (a) In Las Vegas, a convective-limited water collection device with the same width as the disclosed prototype (W = 38 mm) has a simulated annual water capture rate relying on natural wind (blue) within 88% of the solar limit (black). Doubling the wind speed (red) (e.g., forced convection) can result in a capture flux exceeding the solar limit. Thus, a hypothetical one-square-meter device could provide the daily drinking water for two to three adults. The plotted weather data for KLAS airport was obtained from Wolfram Research. (b) Simulated the global convective-limited water capture potential, where some regions exceed 70 kg m -2 d -1 (dark green regions). (c) Lord et al. (8) presented a benchmark curve (green; Equation 11, Example 5) for the performance required for AWH devices to provide safe managed drinking water (SMDW) for one billion people. Relying on 1 m high natural wind, convective-limited water capture, and the disclosed prototype width produced a range of fluxes (blue shaded area represents 95% of the global flux range) that generally exceed the performance required by the Lord curve. Error bars represent 1 SD.

[0046] Figure 41 Shows the FTIR results of the PAAm hydrogel samples. The crosslinker ratio of the samples is 0.1% DETAILED DESCRIPTION

[0047] The present disclosure may be more readily understood by reference to the following detailed description and appendices, which include examples, claims, and drawings that show some but not all of the embodiments of the invention. In fact, the invention may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will satisfy applicable legal requirements. Throughout the text, like reference numerals refer to like elements. It should be understood that the invention is not limited to the particular methods and protocols described, as these may vary. It should be understood that the terms used herein are for the purpose of describing particular embodiments only and are not intended to limit the scope of the invention.

[0048] Benefiting from the teachings presented in the foregoing description and the associated drawings, those skilled in the art to which this invention pertains will envision many modifications and other embodiments of the invention set forth herein. Accordingly, it is to be understood that the invention is not to be limited to the specific embodiments disclosed, and that modifications and other embodiments are intended to be included within the scope of the appended claims. Although specific terms are employed herein, they are used in a general and descriptive sense only and not for purposes of limitation.

[0049] As used herein, unless the context clearly indicates otherwise, the singular forms "a", "an", and "the" optionally include plural referents. For example, the use of the term "a channel" can represent the disclosure of an embodiment in which only a single channel is provided, and can also represent the disclosure of an embodiment in which multiple such channels are provided, unless the context indicates otherwise.

[0050] All technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains, unless otherwise clearly defined.

[0051] As used herein, the term "optional" or "optionally" means that the subsequent described event or circumstance may or may not occur, and the description includes instances where the event or circumstance occurs and instances where it does not occur.

[0052] As used herein, the term "at least one of" is intended to be synonymous with "one or more of". For example, "at least one of A, B, and C" clearly includes only A, only B, only C, and combinations of each.

[0053] In this document, ranges may be expressed as from "about" one particular value and / or to "about" another particular value. When such a range is expressed, on the one hand it includes from one particular value and / or to another particular value. Similarly, when values are expressed as approximations by use of the antecedent "about", it is to be understood that the particular value forms on the other hand. It should be further understood that each endpoint of each range is significant with respect to the other endpoint and independently of the other endpoint. Optionally, in some aspects, when values are approximated by use of the antecedent "about", it is contemplated that values within up to 15%, up to 10%, up to 5%, or up to 1% (higher or lower) of the specifically recited value may be included within the scope of these aspects. Similarly, the use of "substantially" (e.g., "substantially parallel") or "approximately" (e.g., "approximately planar") should be understood to include embodiments in which the angle is within ten degrees, within five degrees, or within one degree.

[0054] As used herein, the term "or" means any one member of a particular list, and in alternative embodiments, unless the context otherwise indicates, may include any combination of members of the list.

[0055] It should be understood that, unless expressly stated otherwise, no method recited herein is intended to be construed as requiring that its steps be performed in a particular order. Accordingly, where a method claim does not actually recite an order to be followed by its steps or where no particular order is otherwise specifically stated in the claims or in the specification, no inference of order is intended in any respect. This applies to any possible non-expressive basis of interpretation, including: logical issues regarding the arrangement of steps or operational flow; plain meaning derived from grammatical organization or punctuation; and the number or type of aspects described in the specification.

[0056] The following description provides specific details to provide a thorough understanding. However, those skilled in the art will understand that the devices, systems, and associated methods of using the devices can be implemented and used without these specific details. In fact, the devices, systems, and associated methods can be practiced by modifying the devices, systems, and associated methods shown, and can be used in conjunction with any other devices and techniques conventionally used in the industry.

[0057] In the following description, various examples of atmospheric water capture devices and methods are disclosed. It is contemplated that each of these embodiments can also be used for atmospheric water collection devices and methods. Further, it should be understood that embodiments and examples of atmospheric water collection devices and methods can also be used for the purpose of water capture.

[0058] Figure 1 An example atmospheric water capture device 10 is shown. The atmospheric water capture device 10 can be configured to convert water vapor into liquid water. Optionally, the device 10 can be powered by natural solar energy. In one aspect, the device may not include a power adapter. The device 10 can include vertically stacked components that achieve simultaneous or substantially simultaneous water capture and distillation.

[0059] The device 10 can include a housing 20 that includes an inlet 22. The inlet 22 can be configured to receive ambient air. The housing 20 can include an air cooling device, such as a fan 26. The fan 26 can be located near the inlet 22 to cool the ambient air entering the housing. Optionally, the cooling device can be battery-powered, solar-powered, or thermoelectric generator-powered. In an exemplary aspect, the housing can have a volume of approximately 0.7 liters. However, other volumes are contemplated.

[0060] The apparatus 10 may further include a basin 30 disposed within the housing. The basin 30 may be configured to distill water vapor from the received ambient atmosphere. The basin 30 may include a first section 32 facing the ambient atmosphere entering the housing (e.g., on the first side of the basin 30). The first section 32 may be configured to draw water from the ambient atmosphere within the housing. Alternatively, the first section 32 may include a first membrane configured to draw water from the ambient atmosphere within the housing. The first section 32 (optionally, the first membrane) may include a capture gel. The basin 30 may include at least one channel 36 configured to store an ionic solution and the water drawn by the first section (optionally, the first membrane). In some optional aspects, the basin 30 may have only a single channel 36. Optionally, the boundary or perimeter of the single channel 36 may be the same as or substantially the same as the basin 30 and / or the housing 20. In other aspects, the basin 30 may include a plurality of channels 36. Optionally, the channels 36 may include a porous hydrogel infused with an ionic solution. In one example, the ionic solution is lithium bromide. The channels 36 may be surrounded by a thermal insulator 50. The thermal insulator may include, for example, polystyrene foam. The basin 30 may include a second section 34 (e.g., positioned on the second side of the basin 30). The second section 34 may include a second membrane. The second section or the second membrane may include an evaporation gel. The second section 34 (e.g., optionally, the second membrane) may be configured to evaporate the water stored in the at least one channel. Optionally, the second section may be disposed opposite the first section. For example, the first section 32 may be on the first side and the second section 34 may be on the second side, where the second side is positioned opposite the first side.

[0061] The housing 20 of the apparatus 10 may further include an outlet 24 configured to dispense the evaporated water. The apparatus 10 may further include a condensing tube 40 connected to the outlet and configured to condense the evaporated water from the outlet 24. The apparatus 10 may further include a reservoir 42 configured to store the condensed water. The reservoir 42 may be connected to the condensing tube 40.

[0062] The apparatus 10 may further include an air heating device, such as a heater 60. The air heating device may be configured to heat the second section 34 (e.g., the second side) of the basin 30. In an exemplary aspect, the heater 60 may include a fuel stove (e.g., a plurality of camping stoves, such as, for example, a STERNO camping stove). In an exemplary aspect, the heater may provide at least 100 watts (e.g., at least 150 watts, about 200 watts, or greater than 200 watts). Thus, the second section 34 may be relatively hot and thus have a higher vapor pressure than the reservoir 42. In a further aspect, the first section 32 may have a lower vapor pressure than the ambient air. The apparatus 10 may further include a radiator 62. The radiator 62 may include a plurality of fins 64. The radiator 62 may include a thermally conductive material (e.g., copper).

[0063] A method may include capturing atmospheric water using an atmospheric capture device. The atmospheric capture device may include any and all details and embodiments described herein. The method may include receiving ambient atmosphere through an inlet. The method may further include cooling the received ambient atmosphere. The method may further include diffusing water from the received ambient atmosphere via a first section of the basin (e.g., optionally, a first membrane). The method may further include storing the water in at least one channel of the basin. The method may include heating a second side of the basin. The method may include evaporating the water stored in the at least one channel via a second section (e.g., optionally, a second membrane). The method may further include condensing the evaporated water. In one aspect, the step of diffusing water from the received ambient atmosphere and the step of condensing the evaporated water occur concurrently.

[0064] Exemplary embodiments

[0065] Additional features and details that may be included in the disclosed embodiments are provided in the following disclosure.

[0066] Example 1:

[0067] Based on Figure 1 A prototype of an atmospheric water capture device is produced as disclosed herein. The proposed device may operate continuously. The device may use available heat resources to pump moisture from a dry environment into a reservoir. The device may include a pump that includes a superabsorbent porous hydrogel core infused with a supersaturated salt solution. A porous, moisture-absorbing gel may be synthesized. The water-to-fuel ratio may exceed the metric of the Defense Advanced Research Projects Agency by 7. The design may be based on detailed heat and mass transfer and thermodynamic analyses (see Figure 2 ).

[0068] Example 2:

[0069] Introduction

[0070] Since the water levels in the southwestern United States are at their lowest in 1200 years, it is imperative to find alternative water sources. See A.P. Williams, B.I. Cook, J.E. Smerdon, Nature Climate Change 12 (2022) 232 - 234. One source is close at hand: there is a hidden ocean of water vapor in the air. Even in a dry environment like Clark County, which uses 260 million gallons of water per day, the same amount of water can be obtained from just 0.1% of the atmosphere. Due to the almost uninterrupted solar irradiation in southern Nevada, approximately 10 kg of water can be collected per day on a solar device footprint of 1 m 2 ( Figure 3)——A device the size of a photovoltaic panel provides more than one person's daily drinking water needs. Globally, solar atmospheric water harvesting (AWH) could supply water to approximately one billion people, according to a recent Nature study. J. Lord, A. Thomas, N. Treat, M. Forkin, R. Bain, P. Dulac, C. H. Behroozi, T. Mamutov, J. Fongheiser, N. Kobilansky, S. Washburn, C. Truesdell, C. Lee, P. H. Schmaelzle, Nature 598 (2021) 611 - 617. However, despite the availability of water vapor, recent studies of new AWH approaches have not demonstrated that in dry environments such as Las Vegas, with an average humidity of approximately 20% relative humidity (RH) and which can drop below 10% RH ( Figure 4 , red), the water collection rate limited by solar energy is 10 kg m -2 / day -1 ( Figure 4 , yellow). See R. Tu, Y. Hwang, Energy 201 (2020) 117630; X. Zhou, H. Lu, F. Zhao, G. Yu, ACS Materials Letters 2 (2020) 671 - 684. There is sufficient water vapor, but no demonstrated collection rate near the solar limit of 10 kg m -2 / day -1 . This fact indicates that this is a transport - limited problem rather than a thermodynamics - limited problem - here, transport refers to the movement of water, energy, and chemicals through various media. The driest conditions demonstrate that the current state - of - the - art is 30% RH, in which case researchers measured less than 0.25 kg m -2 / day -1 , while the highest rate of 2.9 kg m -2 / day -1. H. Kim, S. R. Rao, E. A. Kapustin, L. Zhao, S. Yang, O. M. Yaghi, E. N. Wang, Nature Communications 9 (2018) 1 - 8; X. Wang, X. Li, G. Liu, J. Li, X. Hu, N. Xu, W. Zhao, B. Zhu, J. Zhu, Angewandte Chemie - International Edition 58 (2019) 12054 - 12058; H. Qi, T. Wei, W. Zhao, B. Zhu, G. Liu, P. Wang, Z. Lin, X. Wang, X. Li, X. Zhang, J. Zhu, Advanced Materials 31 (2019) 1 - 9. Recognizing the limitations of the current state - of - the - art and identifying a completely new approach inspired by water - uptake processes that can exist in nature. In preliminary work, the bio - inspired approach showed promise as the humidity for water collection was lower and the rate faster than any other published literature ( Figure 4 , blue). However, to achieve 10 kg m -2 / day -1 ( Figure 4 , green box) at a humidity as low as 10% RH, there is still much research to be done. To achieve this goal, new technologies that can address crucial regional needs can be developed.

[0071] Method

[0072] Existing AWH approaches rely on a single adsorbent material that performs multiple functions sequentially. For example, imagine only being allowed to charge a mobile phone or use it, but not both at the same time. On the other hand, taking the Australian tree frog and air plants as examples, nature takes a completely different approach of using separate dedicated materials to capture water and utilize water simultaneously. C. R. Tracy, N. Laurence, K. A. Christian, The American Naturalist 178 (2011) 553 - 558; P. S. Raux, S. Gravelle, J. Dumais, Nature Communications 11 (2020) 396. Here, soft membranes (such as skin or cuticle) enable water to continuously pass through them and be captured within the extracellular fluid (ECF) region ( Figure 5a). Meanwhile, the water stored in the ECF region can be used for biochemical processes. Thus, nature's way is analogous to being able to use a mobile phone and charge it simultaneously. Inspired by nature, a skin-like hydrogel membrane encapsulating an ionic (lithium bromide) liquid basin can provide a more efficient and elegant way of AWH ( Figure 5 b). Here, water is captured by the capture gel and then stored in the liquid basin where lithium bromide, which reduces humidity, serves as a chemical potential reservoir. L. Greenspan, Humidity Fixed Points of Binary Saturated Aqueous Solutions, n.d. During the day, the stored water can be evaporated through the evaporator gel and then condensed into fresh liquid water. Each of these components can be stacked in a vertically oriented design to enable simultaneous water capture and distillation. The core hypothesis is that, through the disclosed bio-inspired design, the disclosed individual dedicated material approach should outperform the prior art single adsorbents, thus paving the way for achieving efficient water collection performance at solar limits as low as 10% RH and at 10 kg m -2 / day -1 of solar limits.

[0073] Task

[0074] To achieve the performance goals ( Figure 4 , yellow box), there may be three studies: (1) transport processes, (2) materials science, and (3) system prototyping.

[0075] Study 1: Water, Energy, and Chemical Transport Processes

[0076] The transport processes occurring in the proposed design can be modeled to predict and test new AWH designs. High air flow into the capture gel and the low thermal conductivity in the evaporator gel enable high water throughput. Pore-elastic Darcy flow can be assumed to exist within the gel such that the apparent velocity is related to the gradient of the volume strain: At this apparent velocity, the steady-state conservation of mass can be expressed The steady-state conservation of ions and the steady-state conservation of thermal energy The gel deformation can be solved according to the finite strain theory. Only recently have there been attempts to couple some of these PDEs together to understand transport through hydrogels - however, a more complete model that incorporates deformation and swelling-dependent properties does not yet exist; thus, the work presented here can contribute knowledge to the field of liquid-vapor transport. C.D. Díaz-Marín, L. Zhang, B. El Fil, Z. Lu, M. Alshrah, J.C. Grossman, E.N. Wang, International Journal of Heat and Mass Transfer 195 (2022) 123103. Leveraging the experience of building heat transfer experiments, a custom environmental chamber can be used to perform steady-state heat transfer and cycling tests, and virtual object creation imaging is used for in-situ 3D observations( Figure 6 ). In this way, a rich set of validation data as well as mechanical and heat transfer measurements can be provided simultaneously.

[0077] Study 2: Hydrogel Materials Science

[0078] A hydrogel is a network of chain-like polymer molecules that swells or shrinks according to environmental conditions such as osmotic pressure and temperature. Based on preliminary analysis, the composite property called the poroelastic diffusivity D 孔隙弹性 can be maximized such that where κ is the absolute permeability of the gel (m 2 ), K is the elastic bulk modulus of the gel (Pa), and μ is the dynamic viscosity of the liquid (Pa*s). However, maximizing this quantity can be challenging because there may be a fundamental trade-off between permeability and stiffness: increasing one property necessarily decreases the other( Figure 7 ). If this is true, ways to break this trade-off by functionalizing and combining micron-scale channels and pores through freeze-thaw and freeze-drying processing can be explored, thus contributing knowledge to the field of polymer science. N. Annabi, J.W. Nichol, X. Zhong, C. Ji, S. Koshy, A. Khademhosseini, F. Dehghani, Tissue Engineering-Part B: Reviews 16 (2010) 371-383. The idea is to utilize ice crystal nucleation to create large voids in the gel. In addition to increasing D 孔隙弹性In addition, the gel should be highly stretchable to facilitate the formation of the film, as reducing the thickness improves overall transport. Inspired by recent work on highly entangled gels, preliminary work has begun on how to increase the maximum strain to produce strong, stretchable, thin gels. J. Kim, G. Zhang, M. Shi, Z. Suo, Science (1979) 374 (2021) 212 - 216. Additionally, the evaporator gel should be as thermally insulating as possible to minimize heat loss. The Maxwell effective thermal conductivity rule can be applied to hydrogels, enabling the tuning of conductivity via composite materials. K. Pietrak, T. Journal of Power of Technologies 95 (2015) 14 - 24. The combination of low - density insulators can provide low thermal conductivity respectively. Thermal conductivity can be tested by applying temperature boundary conditions via a customized device and a laboratory cooler.

[0079] Study 3: Prototyping and Crowdsourcing of Data from Local High Schools

[0080] A preliminary prototype can be constructed to demonstrate certain aspects of the water collection system ( Figure 8 ). Through prototyping, the effects of separately controlling the capture conditions and the evaporator conditions can be understood.

[0081] A science kit can be designed and inexpensively constructed using a 3D printer and readily available materials. An early iteration of the kit could be a simple solar distillation device for water filtration made of polystyrene and fabric, similar to the evaporator gel in the disclosed system. A Raspberry - Pi - based data recording system can provide a means to crowdsource data from these collection stations. Performance and weather data sent to the cloud can inform research activities to understand the system performance under varying conditions. Annual updates to the design can be implemented in future iterations, introducing new materials and designs. Contribution of new knowledge to existing fields: This work demonstrates how nature can inspire better designs by separately assembling components with dedicated functions. It also demonstrates how the complexity of soft polymer materials can be harnessed to achieve favorable behaviors. It can reveal how the transport properties of polymers and the liquid - vapor phase change behavior respond to complex environments with various gradients that have not been previously studied.

[0082] Example 3: Background Art

[0084] Water is an important substance typically collected from freshwater surface resources (e.g., lakes and rivers), and in the context of climate change, arid regions are facing severe water shortages in these resources. Konapala G, Mishra AK, Wada Y, Mann ME Climate change can affect global water availability through compounding changes in seasonal precipitation and evaporation. https: / / doi.org / 10.1038 / s41467-020-16757-w. In southern Nevada, since 2002, the vulnerability of the water supply has driven aggressive conservation efforts, reducing per capita water use by half. However, despite these conservation efforts, population growth and climate change continue to reduce the water supply in the region ( Figure 9 ) to its lowest level in 1200 years. Brelsford C, Abbott JK (2017) Growing into Water Conservation? Decomposing the Drivers of Reduced Water Consumption in Las Vegas, NV. Ecological Economics, 133:99-110. https: / / doi.org / 10.1016 / j.ecolecon.2016.10.012; US Bureau of Reclamation (2022); LAKE MEAD AT HOOVER DAM, END OF MONTH ELEVATION (FEET); National Park Service (2019) Storage Capacity of Lake Mead; Williams AP, Cook BI, Smerdon JE (2022) Rapid intensification of the emerging southwestern North American megadrought in 2020-2021. Nature Climate Change, 12(3):232-234 https: / / doi.org / 10.1038 / s41558-022-01290-z. Las Vegas, like much of the western United States, receives very little rainfall ( Figure 10a) - Only 6 cm per year. Due to the limited groundwater resources, especially in the case of increased pollution caused by human activities, developing typical alternative sources is not feasible, and desalination is too expensive and impractical for inland areas. Mays LW Groundwater Resources Sustainability: Past, Present, and Future, https: / / doi.org / 10.1007 / s11269-013-0436-7; Pazouki P, Stewart RA, Bertone E, Helfer F, Ghaffour N (2020) Life cycle cost of dilution desalination in off-grid locations: A study of water reuse integrated with seawater desalination technology. Desalination, 491:114584. https: / / doi.org / 10.1016 / j.desal.2020.114584.

[0085] However, in the air around us, there is a hidden and almost infinite water source: water vapor. In southern Nevada, although the area is one of the driest in the world, only 0.1% of the air above southern Nevada can collect 260 million gallons of water used daily. Even at a relatively low humidity of about 20% (the average in Las Vegas), the amount of water vapor in the atmosphere far exceeds the amount of rain precipitation. According to preliminary analysis, if water vapor is captured by a hypothetical ideal collection device (the size of a residential photovoltaic (PV) panel) Figure 10 b), the maximum water capture rate in Las Vegas is about 47 kg m -2 / day -1 - about 300 times more than can be captured from rainwater Figure 10 c). However, existing AWH methods have only demonstrated about 1 kg m -2 / day -1The amount of water collected; thus, the current collection method has no thermodynamic limit - there is enough water in the air. Instead, capturing this water at a meaningful rate requires addressing the problem of limited transport. The conventional method of collecting this water is to thermally condense water vapor to a sub-ambient temperature below the dew point. These methods involve energy-intensive and bulky refrigeration devices such as vapor compression cycles. Tu R, Hwang Y (2020) Reviews of atmospheric water harvesting technologies. Energy, 201:117630. https: / / doi.org / 10.1016 / j.energy.2020.117630. Additionally, in some very dry regions such as Las Vegas, thermal condensation is not feasible because the dew point temperature is below freezing.

[0086] The recent AWH methods physically and chemically capture water in adsorbents and then release the water using solar electricity via evaporation (distillation) or lower critical solution temperature phase separation. Tu R, Hwang Y (2020) Reviews of atmospheric water harvesting technologies. Energy, 201:117630, https: / / doi.org / 10.1016 / j.energy.2020.117630; Zhou X, Lu H, Zhao F, Yu G (2020) Atmospheric Water Harvesting: A Review of Material and Structural Designs. ACS Materials Letters, 2(7):671-684. https: / / doi.org / 10.1021 / acsmaterialslett.0c00130; Zhao F, Zhou X, Liu Y, Shi Y, Dai Y, Yu G (2019) Super Moisture-Absorbent Gels for All-Weather Atmospheric Water Harvesting. Advanced Materials, 31(10):1-7. https: / / doi.org / 10.1002 / adma.201806446; Haddad AZ, Menon AK, Kang H, Urban JJ, Prasher RS, Kostecki R (2021) Solar Desalination Using Thermally Responsive Ionic Liquids Regenerated with a Photonic Heater. Environ. Sci. Technol, 55:52. https: / / doi.org / 10.1021 / acs.est.0c06232. Recent Nature studies have shown that these solar-powered methods could provide drinking water for approximately one billion people.Lord J, Thomas A, Treat N, Forkin M, Bain R, Dulac P, Behroozi CH, Mamutov T, Fongheiser J, Kobilansky N, Washburn S, Truesdell C, Lee C, Schmaelzle PH (2021) Global potential for harvesting drinking water from air using solar energy. Nature, 598(7882):611-617. https: / / doi.org / 10.1038 / s41586-021-03900-w. However, existing AWH methods have a very low yield of approximately 1 kg m. -2 / day -1 (much smaller than typical rainwater harvesting systems) and a solar limit of approximately 10 kg m -2 / day -1 (preliminary analysis as Figure 14(as shown). Lawrence D, Lopes VL (2016) Reliability Analysis of Urban Rainwater Harvesting for Three Texas Cities. Journal of Urban and Environmental Engineering, 10(1): 124 - 134. https: / / doi.org / 10.4090 / juee.2016.v10n1.124134. Distillation can reach this solar limit because recent work on evaporator hydrogels has demonstrated efficiencies > 90% and water fluxes exceeding this solar limit. Shi Y, Ilic O, Atwater HA, Greer JR (2021) All - day fresh water harvesting by microstructured hydrogel membranes. Nature Communications, 12(1): 2797. https: / / doi.org / 10.1038 / s41467 - 021 - 23174 - 0; Guo Y, Zhao F, Zhou X, Chen Z, Yu G (2019) Tailoring Nanoscale Surface Topography of Hydrogel for Efficient Solar Vapor Generation. Nano Letters, 19(4): 2530 - 2536. https: / / doi.org / 10.1021 / acs.nanolett.9b00252; Zhao F, Zhou X, Shi Y, Qian X, Alexander M, Zhao X, Mendez S, Yang R, Qu L, Yu G (2018) Highly efficient solar vapour generation via hierarchically nanostructured gels. Nature Nanotechnology, (6): 489 - 495. https: / / doi.org / 10.1038 / s41565 - 018 - 0097 - z. Thus, existing AWH approaches are significantly limited in the capture phase rather than the distillation phase. To achieve the solar limit for collection (capture + distillation), the approaches focus on developing novel, highly efficient, continuous capture methods while incorporating and improving the best evaporation technologies in a new flow - through architecture.This unique combination of novel and proven materials and technologies, propelled by new science, can offer transformative new ways for AWH. Another issue with existing approaches is the favorable relative humidity conditions (>50% RH), which are difficult to represent in the places where AWH is most needed. Figure 10 c、 Figure 11 a). Thus, existing AWH approaches are not suitable in dry regions such as Las Vegas (20% RH average; as low as 5%). The approach has great promise because preliminary tests have shown that at 10% relative humidity - a condition drier than any existing work - the water capture rate is approximately 1 kg m -2 / day -1 ( Figure 11 ). However, this rate is still far below the solar limit. Achieving such a huge leap in performance at low humidity is possible, but it requires extensive scientific research and entirely new approaches.

[0087] New approach

[0088] The steps involved in AWH can generally be summarized as the following steps:

[0089] I. The first step is water capture, where ambient water vapor (humidity) is condensed into an absorbent or liquid form. This is an exothermic process that releases the latent heat of condensation / absorption.

[0090] II. The next step is water storage, where the water remains within the absorbent or as a solution until it can be released for further processing.

[0091] III. Once a heat source (e.g., the sun) is available, water evaporation absorbs the heat source and converts it into latent heat to evaporate the stored water.

[0092] IV. Finally, water condensation releases the latent heat to the environment, thereby producing nearly pure liquid water. After this step, any subsequent filtration is carried out to remove contaminants.

[0093] Note that "water collection" is sometimes used to describe water distillation (steps III and IV) to purify water from a saline or contaminated liquid source (e.g., Shi Y, Ilic O, Atwater HA, Greer JR (2021) All-day fresh water harvesting by microstructured hydrogel membranes. Nature Communications, 12(1):2797. https: / / doi.org / 10.1038 / s41467-021-23174-0). In the definition of atmospheric water harvesting in this article, the entire four-step process described above is included.

[0094] The current paradigm of AWH involves a single adsorbent material that performs Steps I, II, and III. Many of these approaches rely on solid-state adsorbents such as metal-organic frameworks (MOFs), zeolites, and gels. Kim H, Yang S, Rao SR, Narayanan S, Kapustin EA, Furukawa H, Umans AS, Yaghi OM, Wang EN (2017) Water harvesting from air with metal-organic frameworks powered by natural sunlight. Science, 356(6336):430-434. https: / / doi.org / 10.1126 / science.aam8743; LaPotin A, Zhong Y, Zhang L, Zhao L, Leroy A, Kim H, Rao SR, Wang EN (2021) Dual-Stage Atmospheric Water Harvesting Device for Scalable Solar-Driven Water Production. Joule, 5(1):166-182. https: / / doi.org / 10.1016 / j.joule.2020.09.008; Zhao F, Zhou X, Liu Y, Shi Y, Dai Y, Yu G (2019) Super Moisture-Absorbent Gels for All-Weather Atmospheric Water Harvesting. Advanced Materials, 31(10):1-7. https: / / doi.org / 10.1002 / adma.201806446; Matsumoto K, Sakikawa N, Miyata T (2018) Thermo-responsive gels that absorb moisture and ooze water. Nature Communications, 9(1) https: / / doi.org / 10.1038 / s41467-018-04810-8; Kallenberger PA, M(2018) Water harvesting from air with a hygroscopic salt in a hydrogel-derived matrix. Communications Chemistry, 1(1):28. https: / / doi.org / 10.1038 / s42004-018-0028-9; Guo Y, Guan W, Lei C, Lu H, Shi W, Yu G(2022) Scalable super hygroscopic polymer films for sustainable moisture harvesting in arid environments. Nature Communications, 13(1):1-7. https: / / doi.org / 10.1038 / s41467-022-30505-2. Typically, these technologies have adsorbents that capture and store water (I+II) when the humidity is high at night. During the day, the adsorbent is switched to the desorption mode, isolated from the surrounding environment, and allowed to be heated using a heat source (e.g., solar energy). As the adsorbent is heated, it causes the stored water to evaporate, and the stored water can then be condensed into fresh liquid water through heat exchange with the ambient temperature (III+IV). Some gel-based adsorbents utilize temperature-induced volume changes at high temperatures to directly secrete the stored liquid water.Zhao F, Zhou X, Liu Y, Shi Y, Dai Y, Yu G (2019) SuperMoisture-Absorbent Gels for All-Weather Atmospheric Water Harvesting. Advanced Materials, 31(10): 1-7. https: / / doi.org / 10.1002 / adma.201806446; Matsumoto K, Sakikawa N, Miyata T (2018) Thermo-responsive gels that absorb moisture and ooze water. Nature Communications, 9(1) https: / / doi.org / 10.1038 / s41467-018-04810-8; Guo Y, Guan W, Lei C, Lu H, Shi W, Yu G (2022) Scalable super hygroscopic polymer films for sustainable moisture harvesting in arid environments. Nature Communications, 13(1): 1-7. https: / / doi.org / 10.1038 / s41467-022-30505-2. In all these cases, the collection performance relies on a single adsorbent to perform capture, storage, and removal. Therefore, it is challenging to maximize all three behaviors in a single material. Moreover, solid adsorbents can only perform capture or removal at a given time (. Figure 12a) - Similar to the situation where early portable electronic devices could not be charged and used simultaneously. As an alternative to solid sorbents, recent work on liquid sorbents of high-concentration salt solutions has demonstrated that water capture at one location and water evaporation at another location can occur simultaneously. Wang X, Li X, Liu G, Li J, Hu X, Xu N, Zhao W, Zhu B, Zhu J (2019) An Interfacial Solar Heating Assisted Liquid Sorbent Atmospheric Water Generator. Angewandte Chemie - International Edition, 58(35):12054 - 12058. https: / / doi.org / 10.1002 / anie.201905229; Qi H, Wei T, Zhao W, Zhu B, Liu G, Wang P, Lin Z, Wang X, Li X, Zhang X, Zhu J (2019) An Interfacial Solar - Driven Atmospheric Water Generator Based on a Liquid Sorbent with Simultaneous Adsorption - Desorption. Advanced Materials, 31(43):1 - 9. https: / / doi.org / 10.1002 / adma.201903378. However, due to the exposure of the liquid to the environment and limited performance, there are robustness issues, as the requirement to contain the liquid in a separate basin hinders the full utilization of the solar footprint. It is envisioned that existing liquid sorbent approaches can capture and distill simultaneously, but they cannot fully utilize the solar footprint in the manner of the disclosed devices, systems, and methods.

[0095] However, as demonstrated by tree frogs and air plants, nature has adopted a very different approach of using separate dedicated materials to capture water. Soft membranes (such as a single surface like skin or cuticle; Figure 13 a) Continuously and autonomously capture water - similar to charging and using a battery simultaneously. These membranes surround the extracellular fluid, act as a protective barrier for the organism, and are permeable to water. The extracellular fluid, which is essential for normal hydration and survival, serves as a chemical potential reservoir, allowing water to flow through the skin / cuticle into the liquid. As long as the chemical potential of the extracellular fluid is lower than that of the environmental water vapor, the organism will be hydrated. In other cases, when the environment has a lower chemical potential (dry conditions), the skin / cuticle will act as an evaporation membrane ( Figure 13b). Inspired by nature, it is envisioned that a skin-like gel membrane encapsulating a liquid basin can provide a more efficient and elegant way of AWH. Contrary to existing methods, a unique architecture for separating water capture, storage, and evaporation into three components ( Figure 13 b, Figure 13 c) is proposed, with the concept that separate dedicated materials should be superior to a single material performing all tasks. The hydrogel membrane at the bottom - a capture gel of a completely new material and design - can capture water from the environment faster (Step I). Another membrane at the top serves as an efficient evaporator, where existing work is utilized and improved. Shi Y, Ilic O, Atwater HA, Greer JR (2021) All-day fresh water harvesting by microstructured hydrogel membranes. Nature Communications, 12(1):2797. https: / / doi.org / 10.1038 / s41467-021-23174-0; Guo Y, Zhao F, Zhou X, Chen Z, Yu G (2019) Tailoring Nanoscale Surface Topography of Hydrogel for Efficient Solar Vapor Generation. Nano Letters, 19(4):2530-2536. https: / / doi.org / 10.1021 / acs.nanolett.9b00252; Zhao F, Zhou X, Shi Y, Qian X, Alexander M, Zhao X, Mendez S, Yang R, Qu L, Yu G (2018) Highly efficient solar vapour generation via hierarchically nanostructured gels. Nature Nanotechnology, 13(6):489-495. https: / / doi.org / 10.1038 / s41565-018-0097-z. Sandwiched between these two gels is a storage basin of an ionic solution (liquid desiccant) with an extremely high salinity to ensure absorption even under the driest conditions. Thus, the role of the gel membrane is to permeate water into or out of the basin as quickly as possible, while the role of the basin is to provide a chemical potential reservoir as deep as possible and sufficient storage. By using three dedicated materials optimized for performing capture, storage, and evaporation, transport limitations can be studied to achieve approximately 10 L m -2 / day-1 with limited water flux of solar energy.

[0096] Scientific research

[0097] In order to release the limited flux of solar energy in a dry environment, it is necessary to reveal the scientific research that determines the flow bottleneck. Specifically, the focus is on the material and heat transport limitations during capture and evaporation.

[0098] Transport considerations during capture

[0099] To understand the transport in the capture gel, first consider as Figure 15As shown, the ionic solution in the basin represents a chemical potential reservoir, thus raising the boiling point of water, lowering the freezing point, and reducing the equilibrium relative humidity (RH). Greenspan L Humidity Fixed Points of Binary Saturated Aqueous Solutions. Journal of Research of the National Bureau of Standards - A. Physics and Chemistry, 81(1). As the RH near the solution decreases, the water vapor density ρ also decreases. If the RH of the environment is greater than that of the solution at a similar temperature, water vapor will spontaneously migrate towards the solution and condense into the solution - a well-known phenomenon utilized by liquid desiccants. Chen X, Riffat S, Bai H, Zheng X, Reay D (2020) Recent progress in liquid desiccant dehumidification and air-conditioning: A review. Energy and Built Environment, 1(1): 106-130. https: / / doi.org / 10.1016 / j.enbenv.2019.09.001. Instead of directly exposing the liquid desiccant (basin) to ambient air, the captured gel can be membrane-bound, thus facilitating transport, providing protection against external elements, and enabling a vertically oriented design to fully utilize the solar footprint.Wang X, Li X, Liu G, Li J, Hu X, Xu N, Zhao W, Zhu B, Zhu J (2019) An Interfacial Solar Heating Assisted Liquid Sorbent Atmospheric Water Generator. Angewandte Chemie - International Edition, 58(35): 12054 - 12058. https: / / doi.org / 10.1002 / anie.201905229; Qi H, Wei T, Zhao W, Zhu B, Liu G, Wang P, Lin Z, Wang X, Li X, Zhang X, Zhu J (2019) An Interfacial Solar - Driven Atmospheric Water Generator Based on a Liquid Sorbent with Simultaneous Adsorption - Desorption. Advanced Materials, 31(43): 1 - 9. https: / / doi.org / 10.1002 / adma.201903378. Gels that are permeable to both counterions and water also reduce the RH, ρ, of the vapor near the gel - air interface. 表面 , thus enabling atmospheric water capture - a phenomenon that can be verified with preliminary results ( Figure 14 , left). Therefore, water vapor flows from the environment to the gel - air interface in the direction of lower vapor pressure or equivalently in the direction of water vapor density ρ, as they are proportional. Thus, from the perspective of external water vapor mass transfer, the captured water mass flux rate j is:

[0100] j = h 质量传递 (ρ 环境 - ρ 表面 )

[0101] where j is the capture rate that should be maximized, ℃ 质量传递 is the water vapor mass transfer coefficient outside the gel and is set by advection and liquid - vapor condensation, ρ 环境 is set by the environment, and ρ 表面 is set by the gel properties. To maximize water capture, h 质量传递 can be increased. To quantify and increase h 质量传递, it is necessary to study the airflow and boundary layer effects and explore a new hydrogel-mediated dropwise condensation mode driven by salinity-induced chemical potential difference (instead of the typical heat-induced condensation) found in the preliminary tests (Task 1). ρ 环境 It cannot be changed because it is set by the ambient temperature and humidity. Finally, the vapor density ρ on the gel surface can be reduced by manipulating the capture gel and the basin. 表面 . To accurately quantify and control ρ 表面 , it may be necessary to deeply explore the complex multi-physical transport phenomena occurring inside and around the capture gel (Task 2).

[0102] From a chemical perspective, ρ 表面 can be reduced by using a highly hygroscopic salt at its saturation concentration, such as lithium bromide (LiBr). Chen X, Riffat S, Bai H, Zheng X, Reay D (2020) Recent progress in liquid desiccant dehumidification and air-conditioning: A review. Energy and Built Environment, 1(1): 106 - 130. https: / / doi.org / 10.1016 / j.enbenv.2019.09.001. Since saturated LiBr has an equilibrium RH of 6% - 7% at typical ambient temperatures, which represents the lowest RH at which atmospheric water collection can be carried out using LiBr, water capture can be achieved 95% of the time in Las Vegas. From a thermal perspective, ρ 表面 can be reduced by ensuring that the gel surface temperature is as low as possible. Without active refrigeration, the lowest possible temperature is the ambient temperature. However, since latent heat is absorbed / condensed and released when water is captured, the true surface temperature will increase slightly (preliminary finite element method (FEM) modeling illustrates this heating in Figure 17 ). Kim H, Cho H-JJ, Narayanan S, Yang S, Furukawa H, Schiffres S, Li X, Zhang Y-B, Jiang J, Yaghi OM, Wang EN (2016) Characterization of Adsorption Enthalpy of Novel Water-Stable Zeolites and Metal Organic Frameworks. Scientific Reports, : 1 - 8. Due to the condensation of water vapor, it will be necessary to remove an amount equal to the mass flow rate multiplied by the specific latent heat m·h via convection with the environment and conduction through the gel. fgheat. Thus, forced air flow (which also aids in vapor mass transfer via h 质量传递 for vapor mass transfer) and high gel thermal conductivity remove latent heat to the environment. Preliminary modeling has shown that increasing the Biot number for vapor mass transfer increases the capture rate ( Figure 14 , bottom right).

[0103] Finally, understanding mass transfer through the gel will provide information on how to reduce ρ 表面 and maximize capture. Inside the gel, water permeates towards the basin due to the driving liquid pressure gradient . Treating the gel as a porous medium ( Figure 16 ), the effective "pores" are the spacing between polymer chains, where the mesh size ξ is approximately 10 nm depending on the swelling state - thus, the gel has an effective permeability κ. Gennes P-G de (1979) Scaling Concepts in PolymerPhysics.http: / / books.google.com / books? id=ApzfJ2LYwGUC&printsec=frontcover&dq=intitle:Scaling+Concepts+inauthor:de+gennes&hl=&cd=1&source=gbs_api;Offeddu GS,Axpe E,Harley BAC,Oyen ML(2018)Relationship between permeabilityand diffusivity in polyethylene glycol hydrogels.AIP Advances,8(10)https: / / doi.org / 10.1063 / 1.5036999. Treating the gel as an elastically deformable material, the driving pressure gradient can be related to the gradient of the volume (swelling) strain , i.e., where K is the gel bulk modulus. In recently published work, it was demonstrated that this poroelastic description is applicable to hydrogels in an equilibrium environment; the proposed study will explore how this poroelastic description continues to hold when stress / strain, pressure, salt concentration, and temperature gradients are present. Gao Y, Chai NKK, Garakani N, Datta SS, Cho HJ (2021) Scaling laws to predict humidity-induced swelling and stiffness in hydrogels. Soft Matter, 17(43):9893-9900. https: / / doi.org / 10.1039 / D1SM01186C. Combining the poroelastic description with Darcy's law, water moves down the gradient of the volume strain, approximated in 1D as

[0104]

[0105] where ρ1 is the liquid density, μ is the liquid dynamic viscosity, and L is the gel thickness. Here, the quantity κK / μ [m 2 s -1 forms a combined transport quantity called the poroelastic diffusivity D 孔隙弹性 that describes the infiltration velocity - preliminary experiments have determined the value for simple hydrogels to be approximately 10 -10 m 2 / s. Louf J-F, Datta SS (2021) Poroelastic shape relaxation of hydrogel particles. Soft Matter, 17(14):3840-3847. https: / / doi.org / 10.1039 / D0SM02243H. According to this analysis, the gel permeability and stiffness should be maximized while keeping it as thin as possible to capture water at a faster rate. To aid in understanding the complex multi-physics transport problems within and around the gel, dimensional analysis was used to identify important dimensionless parameters. In this way, an organized and intuitive map of the complex multi-physics transport space as shown in Table 1( Figure 23 ) can be constructed. Some of these multi-physics processes within and around the gel are illustrated in preliminary FEM modeling( Figure 17 ).

[0106] Transport considerations during evaporation

[0107] In the evaporator gel, the same flux balance between liquid penetration and vapor transport as in the condenser gel also applies. Here, the vapor driving force is the result of the higher vapor pressure at the evaporator and the saturated vapor conditions (dew condensation) at the cooler ambient temperature condenser. Similar to the capture gel, to maximize u, it is important to maximize κ, K, and ℃ 质量传递 and minimize L. However, the main limitation at the evaporator will be to utilize as much solar heat as possible to drive evaporation. According to the energy balance at the evaporator gel-air interface,

[0108]

[0109] the radiative solar input q" 太阳能 some of which is directed towards evaporation uρ1h fg flow, while some is directed towards conduction and emission losses, where ΔT is the temperature difference across the evaporator gel. Therefore, to maximize the water flux for a given solar heat input, it is important to minimize the conductivity of the evaporator gel as much as possible. Since low thermal conductivity is opposite to that required for the capture gel, ways to tune the hydrogel properties should be explored. The intention is to change the properties by functionalization and incorporating composite materials. For example, a floating hydrogel composite with insulating solar absorption properties as shown in Figure 14 (upper right) has been preliminarily prepared.

[0110] There are further scientific questions to be explored in polymer gel-mediated phase change heat transfer. Given the nanoporous nature of these gels, capillary action is expected to play an important role during evaporation. It is speculated that these surface tension effects significantly compress the hydrogel at the evaporation interface, thereby affecting the transport behavior. Recent investigations of solar distillation using hydrogels have shown surprisingly efficient solar thermal-to-evaporation conversion, approaching kinetic limits unattainable at normal liquid-vapor interfaces. Shi Y, Ilic O, Atwater HA, Greer JR (2021) All-day fresh water harvesting by microstructured hydrogel membranes. Nature Communications, 12(1):2797. https: / / doi.org / 10.1038 / s41467-021-23174-0; Guo Y, Zhao F, Zhou X, Chen Z, Yu G (2019) Tailoring Nanoscale Surface Topography of Hydrogel for Efficient Solar Vapor Generation. Nano Letters, 19(4):2530-2536. https: / / doi.org / 10.1021 / acs.nanolett.9b00252; Zhao F, Zhou X, Shi Y, Qian X, Alexander M, Zhao X, Mendez S, Yang R, Qu L, Yu G (2018) Highly efficient solar vapour generation via hierarchically nanostructured gels. Nature Nanotechnology, 13(6):489-495. https: / / doi.org / 10.1038 / s41565-018-0097-z. This suggests that gel mediation can provide beneficial effects localized at the evaporation interface.

[0111] Research Plan

[0112] To explore the proposed gel-based water collection method, the following three main research tasks can be completed: (1) study the heat and mass transport bottlenecks, (2) reveal the transport-related material physics that determines the material bottlenecks, and (3) study the system behavior and discover prototype designs that operate under a wide variety of conditions.

[0113] Task 1: Study Heat and Mass Transport

[0114] In Task 1, the topics of heat and mass transfer specific to the proposed AWH approach can be studied. Important bottlenecks can be identified and different transport scenarios can be classified in the context of dimensionless variables that quantify the competition between different physical phenomena (Table 1, Figure 23 ).

[0115] Task 1a: Model and simulate transport in different domains. It can be assumed that there is poroelastic Darcy flow within the gel such that the apparent velocity is related to the gradient of the volume strain: At this apparent velocity, the steady-state conservation of mass can be expressed The steady-state conservation of ions and the steady-state conservation of thermal energy The preliminary FEM results of these equations are as Figure 17As shown. At the same time, the gel deformation can be solved according to the finite strain theory. Until recently, attempts have been made to couple some of these PDEs together to understand the transport through hydrogels - however, there is currently no more complete model that combines, for example, deformation and swelling-dependent properties. Díaz-Marín CD, Zhang L, Fil B El, Lu Z, Alshrah M, Grossman JC, Wang EN (2022) Heat and mass transfer in hygroscopic hydrogels. International Journal of Heat and Mass Transfer, 195:123103. https: / / doi.org / 10.1016 / J.IJHEATMASSTRANSFER.2022.123103. Thus, as the best way to handle certain complexities is determined, the final form of the PDE can evolve. For example, the poroelastic diffusion coefficient can vary non-linearly with other properties and gradients of humidity, osmotic pressure, concentration, and capillary pressure. Thus, a new theoretical basis for how to model transport through soft polymeric materials with spatially varying properties can be broken. In any case, a custom finite element method (FEM) approach can be used to solve the governing equations, leveraging expertise in solving custom PDEs to solve challenging transport problems in unconventional soft matter systems. Cho HJ, Lu NB, Howard MP, Adams RA, Datta SS (2019) Crack formation and self-closing in shrinkable, granular packings. Soft Matter, 15(23):4689-4702. https: / / doi.org / 10.1039 / C9SM00731H. Due to the complexity of this modeling, an additional set of physics (essentially PDEs) can be coupled approximately once a year, allowing sufficient time for experimental verification.

[0116] Task 1b: Verify the transport model experimentally. The transport model through the capture and evaporator gels can be tested by varying the gel material properties (Task 2) and exposing it to varying temperature and humidity conditions. Leveraging the experience of building heat transfer experiments, a custom environmental chamber can be used to perform steady-state heat transfer and cycling tests, and virtual object creation imaging can be used for in-situ 3D observation ( Figure 18)。In this way, a rich set of validation data as well as mechanical and heat transfer measurements can be provided simultaneously. The timing of validation can follow the newly added computational model (Task 1a) and the newly discovered material property relationships (Task 2). Through well-controlled experiments, the unknown transport kinetics observed in the preliminary work can be determined ( Figure 11 b).

[0117] Task 1c: Explore the local phase change effect. The liquid-vapor phase change process occurring at the gel-air interface represents one of the least understood sets of phenomena to be encountered. Preliminary tests have shown that dropwise condensation may occur at the captured gel, complicating the assessment of mass transfer and heat transfer coefficients ( Figure 19 ). If the observed effect is true dropwise condensation, wettability and droplet nucleation will play important roles. Based on preliminary results, it is indicated that the wetting characteristics change significantly between the highly swollen state and the partially swollen state, meaning that the dropwise to filmwise transition may be related to humidity. Additionally, unlike traditional condensation where removal must occur, here the droplets are "removed" via absorption and penetration through the gel itself - a very different and unstudied process that may be encountered in nature. On the evaporator side, capillary action is expected to play an important role in setting the outlet boundary conditions for water. Currently, it is an open question how some hydrogels effectively mediate heat transfer at near kinetic limit rates. Zhao F, Zhou X, Shi Y, Qian X, Alexander M, Zhao X, Mendez S, Yang R, Qu L, Yu G (2018) Highly efficient solar vapour generation via hierarchically nanostructured gels. Nature Nanotechnology, 13(6):489-495. https: / / doi.org / 10.1038 / s41565-018-0097-z. One risk of the study is that the radiation of one sun may not be sufficient to heat the evaporation surface above the high boiling point of the ionic solution - however, preliminary analysis indicates that this is possible. Nevertheless, the contingency plan may fall back to a solar-assisted solution where additional heating power will be provided by an external power source. Based on the trajectory of the preliminary exploration, the captured gel can be continued to be studied before the evaporator gel. The results of Task 1c can be fed into the model of Task 1a.

[0118] Task 2: Reveal material physics and unlock new collection capabilities

[0119] The hypothesis is the poroelastic diffusivity, It must be as high as possible to achieve a high water throughput through the gel. This involves increasing the permeability κ and the stiffness K. On the other hand, the thermal conductivity needs to be tuned for the capture gel and the evaporator gel separately. All of these behaviors need to be studied in the context of varying gradients.

[0120] Task 2a: Utilize polymer chemistry and structure to increase the pore elastic diffusivity. Generally, hydrogels can be modified by crosslinking. Gao Y, Chai NKK, Garakani N, Datta SS, Cho HJ (2021) Scaling laws to predict humidity-induced swelling and stiffness in hydrogels. Soft Matter, 17(43):9893-9900. https: / / doi.org / 10.1039 / D1SM01186C. Using a custom-built permeation cell, preliminary results indicate that lower crosslinking increases the permeability ( Figure 20 ). To better guide the optimization of permeability, the microstructure of the gel can be characterized using scanning electron microscopy (SEM). Like permeability, stiffness can also be modified by crosslinking (e.g., methylene bisacrylamide in polyacrylamide). However, using a custom-built indentation testing machine, preliminary results indicate that stiffness responds inversely to permeability ( Figure 20)。Gao Y, Chai NKK, Garakani N, Datta SS, Cho HJ (2021) Scaling laws to predict humidity-induced swelling and stiffness in hydrogels. Soft Matter, 17(43): 9893-9900. https: / / doi.org / 10.1039 / D1SM01186C. This trade-off effect may fundamentally stem from the average spacing between polymer gels. The semi-dilute polymer physics can be combined to confirm this relationship. Gennes P-G de (1979) Scaling Concepts in Polymer Physics. http: / / books.google.com / books?id=ApzfJ2LYwGUC&printsec=frontcover&dq=intitle:Scaling+Concepts+inauthor:de+gennes&hl=&cd=1&source=gbs_api. If this is true, ways to break this trade-off behavior can be explored by functionalizing and combining micron-scale channels and pores through freeze-thaw and lyophilization processing. Annabi N, Nichol JW, Zhong X, Ji C, Koshy S, Khademhosseini A, Dehghani F (2010) Controlling the porosity and microarchitecture of hydrogels for tissue engineering. Tissue Engineering-Part B: Reviews, 16(4): 371-383. https: / / doi.org / 10.1089 / ten.teb.2009.0639. The idea is to utilize the nucleation of ice crystals to generate large voids in the gel. Based on the preliminary measurements of permeability and stiffness, D 孔隙弹性 is about 10 -10 m 2 s -1 . Based on geometric and fluid flow parameters, combining large-scale channels can increase it by an order of magnitude, consistent with the goal of increasing the order-of-magnitude capture rate ( Figure 11 a). Therefore, a target metric of about 10 -9 m 2 s -1 can be set. In addition to increasing D 孔隙弹性In addition, the gel should be highly stretchable to facilitate the formation of the film, as reducing the thickness L improves overall transport. Inspired by recent work on highly entangled gels, preliminary work has begun on how to increase the maximum strain to produce strong, stretchable, thin gels. Kim J, Zhang G, Shi M, Suo Z (2021) Fracture, fatigue, and friction of polymers in which entanglements greatly outnumber cross-links. Science, 374(6564):212-216. https: / / doi.org / 10.1126 / science.abg6320.

[0121] Task 2b: Characterize the response to thermal, humidity, pressure, and ion concentration gradients. Under AWH operation, the gel can be subjected to a variety of different gradients. Building on previous work that applied semi-dilute polymer physics to develop scaling laws describing humidity and swelling dependence, it is expected that thermal and ion concentration differences can give rise to similar scaling laws. Gao Y, Chai NKK, Garakani N, Datta SS, Cho HJ (2021) Scaling laws to predict humidity-induced swelling and stiffness in hydrogels. Soft Matter, 17(43):9893-9900. https: / / doi.org / 10.1039 / D1SM01186C. When these conditions vary spatially, the way the material responds can be explored (e.g., whether stiffness responds to gradients in local swelling or ion-mediated osmotic pressure; whether there are differences between humidity gradients and ion concentration gradients in terms of the permeability and stiffness responses that can be explored). At high salt concentrations, there is a possibility of salt fouling. This can be prevented by ensuring that the poroelastic diffusivity is greater than the ionic diffusivity ( Table 1, Figure 23 ); however, since it is currently unclear, the variation of ionic diffusivity at high concentrations within the hydrogel can be explored.

[0122] Task 2c: Discover ways to modify and tune the thermal conductivity. As previously explained, the capture gel should be as conductive as possible to reduce ρ 表面 and maximize water throughput. On the other hand, the evaporator gel should be as thermally insulating as possible to minimize heat loss. The Maxwell effective thermal conductivity rule can be applied to hydrogels, enabling the tuning of conductivity via composite materials. Pietrak K, T(2015) A review of models for effective thermal conductivity of composite materials. Journal of Power of Technologies, 95(1):14-24. The combination of low-density insulators or conductive metal grids can provide low and high thermal conductivities, respectively. The thermal conductivity can be tested by applying temperature boundary conditions via a customized device and a laboratory cooler. The specific heat capacity and latent heat changes can be tested using differential scanning calorimetry (DSC) along with characterization techniques. Kim H, Cho H-JJ, Narayanan S, Yang S, Furukawa H, Schiffres S, Li X, Zhang Y-B, Jiang J, Yaghi OM, Wang EN (2016) Characterization of Adsorption Enthalpy of Novel Water-Stable Zeolites and Metal Organic Frameworks. Scientific Reports,:1-8. The biggest risk in Task 1 may be that the tunability of the thermal conductivity may be very limited. The contingency plan may be to study geometric means (e.g., surface area increase and gel thinning) rather than material properties to achieve the desired heat transfer characteristics.

[0123] Task 3: Modeling system dynamics in a changing environment and discovering new prototypes

[0124] In Task 3, understanding the behavior of the entire system may be the focus, thus providing valuable insights into how to design and operate the AWH approach in different environments.

[0125] Task 3a: Modeling the system behavior under different conditions. The approaches include transistor-like systems, where the system behavior depends entirely on the operating conditions. Therefore, using weather data collected from Wolfram Research and the National Solar Radiation Database, the performance across the country can be simulated ( Figure 10(The ability to perform these types of calculations is demonstrated). Wolfram Research, Research W (2014) Weather Data. https: / / reference.wolfram.com / language / ref / WeatherData.html; NREL (2021) National Solar Radiation Database. https: / / nsrdb.nrel.gov / . Changes in condensation and evaporation rates can be calculated using time-dependent data as Figure 21 shown. The system can be controlled and regulated to ensure that the liquid basin does not deplete to a low level or accumulate beyond the container capacity. Ideally, this control scheme can be passive, where a fixed amount of salt ensures that the condensation rate slows down as the basin fills (since the concentration decreases and the RH increases). Conversely, if the evaporation is too fast and the basin is depleted, the concentration increases, raising the boiling point to slow down the evaporation. Therefore, there is a potential passive control mechanism by designing the basin and the amount of ions that can be explored and modeled.

[0126] Task 3b: Build and test a prototype device for testing in the laboratory and in the field. It is often found that students learn faster from physical prototypes and experiments than from models and descriptions alone. A preliminary prototype has been built to demonstrate some aspects of the water collection system ( Figure 22 ). Through continuous iteration, the capture rate in a controlled environment, geometric features such as surface area enhancement, evaporator performance under heaters and solar simulators, incorporating composite evaporator gels, understanding the dynamics of the diurnal cycle in different environments, etc. may be the focus. Thus, the effects of separately controlling the capture conditions and the evaporator conditions can be understood.

[0127] Task 3c: Water quality testing. To demonstrate a broader impact on solving the water shortage problem, the collector should be safe to use. The quality of the collected water can be tested. One risk of this task is that distillation may not remove ions or other contaminants completely to potable levels. For example, the lithium ion content in water should be less than <10 μg / L - a metric target for evaluation. Lindsey BD, Belitz K, Cravotta CA, Toccalino PL, Dubrovsky NM (2021) Lithium in groundwater used for drinking - water supply in the United States. Science of The Total Environment, 767:144691. https: / / doi.org / 10.1016 / J.SCITOTENV.2020.144691. Contingency measures include further filtration, reverse osmosis, or considering using the collected water for non - potable uses. In any case, the results of this water quality testing can also guide further research on how to improve the method or incorporate further filtration / purification. Example 4:

[0128] The following examples contain additional details regarding the disclosed systems and methods. The examples describe an aspect of the present disclosure that describes the path of water traversing through a gel material from vapor to liquid form for humidity control in an aircraft carrier. The examples describe the process of water in vapor form (in this case, water vapor in an aircraft cockpit) moving towards and through a condensation gel. In one aspect, the condensation gel is a solid ion gel condenser. In one aspect, the condensation gel can be a hydrogel material (e.g., a water - absorbent polymer material) that condenses water vapor on or within the hydrogel material. The condensed water moves through the condensation gel to a liquid desiccant. In one aspect, the liquid desiccant can be a salt solution. The atmospheric water collection device disclosed herein can similarly capture water vapor from ambient air and transfer the condensed vapor to a liquid desiccant (i.e., a salt solution) using the same or similar materials and processes disclosed in the appendix. However, although the atmospheric water collection device can further distill, filter, and / or purify / separate the captured water to produce pure liquid water form, the examples describe a further process of discarding the captured water for aircraft humidity removal.

[0129] In the described example, research was conducted on multifunctional ionogel condenser materials for thermal and humidity control. For the development of lightweight and reliable aircraft and to provide a safe operating environment for crew members, proper temperature control, moisture removal, and dehumidification of the air supplied to the cabin or cockpit are necessary. A hydrogel material embedded with salts - called an ionogel - was envisioned for effectively controlling temperature, removing moisture, and regulating humidity. The ionogel offers thermophysical properties similar to liquid water but has the mechanical properties of a solid. This solid, water-like material opens up new design spaces where transport can be maximized through high-surface-area geometries and system complexity can be reduced by leveraging the inherently multifunctional behavior of the gel. Specifically, the gel is multifunctional because it can act as a filter trap for removing small droplet moisture from the air, a high-surface-area heat exchanger for temperature control, a condenser for dehumidifying moist air, and an evaporator for humidifying dry air. To explore this potential technology, the following objectives were pursued.

[0130] 1. Synthesize and optimize the material properties of the ionogel material, where a polyacrylamide-based hydrogel with high crosslinking and porous cavities was envisioned to provide high water throughput

[0131] 2. Model and simulate the transport of water, salts, and heat through the ionogel material, where high mechanical stiffness, high permeability, high thermal conductivity, and small condenser length scales were envisioned to provide optimal performance

[0132] 3. Fabricate and optimize an ionogel condenser in a sphere array using the synthesized material and design parameters obtained from the models and simulations.

[0133] This work could pave the way for responsive hydrogels for autonomous thermal, moisture, and humidity control, enabling safer and more maneuverable aerospace vehicles and platforms to provide unprecedented performance characteristics for Air Force applications.

[0134] Research work

[0135] 4.1 Motivation

[0136] Proper air conditioning on an aircraft is crucial for pilot performance and safety [1] as well as aircraft reliability [2]. Such conditioning includes temperature control, moisture removal, and humidity regulation. Traditionally, air conditioning is performed in an environmental control system (ECS) [3] - a complex system consisting of mixers, pumps, and heat exchangers - which combines ram air (cold air from the outside) and bleed air (hot air from the engine) to supply conditioned air to the cockpit and / or cabin. Moisture removal is a key task of the ECS because moisture poses serious hazards such as corrosion, which can potentially impede the structural integrity of the aircraft [4]. For the Air Force, a previous study found that moisture often enters the F-16 cockpit through condensation, open canopies, the ECS, and other paths [5]. This moisture is absorbed and retained within the insulation blankets, which are common barriers in aircraft [6]. Without proper drainage, water can damage protective coatings, cause corrosion, and even promote the growth of harmful microorganisms [5].

[0137] Moisture can come from two sources: (1) small droplets flowing in the air and (2) humid air that can condense liquid water on cold surfaces. Traditional ECS systems only achieve the first type of moisture removal, so-called moisture extraction, rather than dehumidification, which addresses the second type. This moisture extraction occurs in a water separator ( Figure 24 ), which is a physical filter / barrier that removes small droplets. However, the water separator does not dehumidify the air; thus, the air can remain humid and can condense on any surface below the dew point. The dew point is the temperature below which water condenses ( Figure 25 ). As long as the surfaces inside the aircraft remain above the dew point, no moisture will form. Since the dew point increases with humidity, in order to provide maximum protection against moisture formation, the relative humidity should be as low as possible. Therefore, dehumidifying the air can increase the safety margin for operating the aircraft. However, for optimal crew comfort and performance, the humidity should not be too low (<20%) [7,8]. Therefore, there is a need to regulate the humidity to around the target level in a simple and lightweight package. To meet this need, the use of an ionogel-based condenser with a solid-state design is envisioned, which provides the following multifunctional behavior: (1) regulate the humidity to the target level, (2) directly remove moisture droplets from the air, and (3) control the air temperature to the desired level. Additionally, since the condenser design relies on the natural behavior of the ionogel material, the humidity regulation in the disclosed approach is autonomous.

[0138] 4.2 Background

[0139] Background information on the ideal air conditions for an aircraft is provided, followed by a discussion of the existing approaches for achieving these conditions and a subsequent discussion of the physical principles of the approaches disclosed below.

[0140] 4.2.1 Ideal air conditions

[0141] The US military has established the cockpit air condition standards and requirements specified in Military Standard MIL-E-18927E(AS).

[0142] The following Table 1 lists some key requirements.

[0143] Table 1: Air delivery requirements according to Military Standard MIL-E-18927E(AS)

[0144]

[0145] The military standard uses an effective temperature called Wet Bulb Globe Temperature (WBGT) to evaluate thermal comfort. WBGT takes into account humidity and radiation. Specifically, WBGT is the weighted average of the wet bulb temperature, the globe temperature, and the dry bulb temperature (all measured in degrees Celsius):

[0146] WBGT = 0.7 湿球 + 0.2 黑球 + 0.1 干球 (1)

[0147] WBGT was developed in the 1950s to combat heat stress in soldiers, but it has deficiencies and limitations in capturing the effects of humidity and sweat [9]. WBGT weights the wet bulb temperature more heavily than the true temperature of the air (dry bulb temperature). The WBGT requirement is also inconsistent with the aircraft interior humidity requirement where the dew point must be greater than 4.4 °C. For example, operating at a tennis temperature of 20 °C, a globe temperature of 0 °C (no radiation), and a dry bulb temperature of 21 °C results in an acceptable WBGT of 16.1 °C, but an unacceptably high dew point temperature of 19.4 °C, leading to a high humidity environment. The wet bulb temperature may even increase to above saturation, which almost ensures destructive condensation inside the cockpit and still remains within the comfort level defined by WBGT. Due to the limiting weighting of WBGT to the wet bulb temperature, to meet the maximum dew point temperature requirement of 4.4 °C, the true (dry bulb) air temperature would need to be 39 °C, which is incredibly warm for human comfort and far exceeds the maximum indoor temperature of 28 °C of the ASHRAE 55 standard. In fact, in the absence of significant radiant heat sources (e.g., night flights or crew in covered sections), it is absolutely impossible to meet the military standard WBGT requirement, the military standard dew point requirement, and maintain a comfortable temperature (as defined by ASHRAE). Therefore, based on the incompatibility of the standards, reports of moisture accumulation in military aircraft [5], and the fact that traditional ECS systems cannot dehumidify the air, the humidity levels in practice are very likely to exceed the design specifications.

[0148] Rather than relying on WBGT requirements defined by military specifications to find the optimal air conditions, the disclosed method relies on the maximum humidity dew point requirement (not to exceed 4.4 °C) defined by military specifications, the ASHRAE 55 temperature specification, and the results of a large number of studies which show that significant crew discomfort may occur at humidities below approximately -20% [8]. Among these specifications, there is an ideal air condition region, as Figure 36 shown and detailed in Table 2 below.

[0149] Table 2: Ideal air conditions defined by a series of standards and studies

[0150]

[0151] 4.2.2 Existing air conditioning methods

[0152] As previously mentioned, traditional ECS systems use physical separation techniques to remove moisture from the air, but cannot directly dehumidify the air itself [3]( Figure 24 ), resulting in documented examples of moisture and corrosion [5]. One way to dehumidify the air is to use thermal separation techniques, where water vapor in the humid air condenses on a cold condenser before being delivered to the cockpit / cabin. This thermal separation requires the cold condenser to be below the dew point temperature. To this end, a cold source (such as from ram air) needs to be introduced into the ECS via one or more heat exchangers, increasing the complexity and weight of the system. In newer ECS systems, an electronically controlled vapor compression cycle (VCC) is typically used to achieve this low temperature

[10] . VCC - commonly used in refrigeration and HVAC - uses the evaporation and condensation of a refrigerant to achieve these low temperatures. However, VCC increases the significant system weight, volume, and complexity, as shown in Figure 27. Therefore, a simple moisture removal and dehumidification system with a smaller footprint is needed for cabin / cockpit air delivery.

[0153] 4.2.3 Liquid drying methods

[0154] Rather than relying on physical and / or thermal separation techniques, the disclosed approach relies on chemical separation techniques. This technique exploits the tendency of a chemical substance - in this case water - to migrate towards a lower chemical potential. One way to create a chemical potential reservoir is to add salt to liquid water, thereby creating a salt solution. This lowering of the chemical potential is evident in the humidity near the liquid solution. In pure water, the relative humidity very close to the liquid-vapor interface is 100%. However, in a saturated sodium chloride solution, this relative humidity is approximately 75%

[11] . In the case of different salts, this humidity can be further reduced, for example, with lithium chloride, and the relative humidity can even be as low as 7%

[11] . Due to its low humidity, the salt solution or liquid desiccant can spontaneously absorb water from humid air (dehumidification), as long as the humidity is higher than the equilibrium value of the salt solution, as shown in Figure 28. In order to Figure 26 deliver ideal aircraft cockpit / cabin air under the strictly defined conditions shown in Table 2, a saturated potassium acetate solution would be an ideal liquid desiccant candidate because its equilibrium humidity values are approximately 21% to 22% over a wide temperature range, as Figure 29 shown. Additionally, as a food safety chemical, potassium acetate does not pose a hazard to the health and safety of the flight crew.

[0155] Liquid desiccant systems are a relatively mature technology and have been proven effective as dehumidifiers in commercial air conditioning systems

[12] . However, such systems have not been implemented for aerospace applications. The challenge in implementing liquid desiccants is that they must flow through complex heat exchangers, involving air flow, spray liquid desiccant flow, and cooling water flow (see Figure 30). When the liquid desiccant is sprayed, the large liquid-vapor surface area provides sufficient heat and mass transfer area for rapid dehumidification of the air flowing transversely to the spray.

[0156] Dehumidification is an exothermic process, and therefore, it is necessary to cool the air by an amount equivalent to the latent heat of phase change. This cooling is provided by a separate water flow through a finned heat exchanger. The sprayed desiccant falls downward under the influence of gravity and is collected at the bottom. Therefore, these systems rely on a consistent direction of gravity. Given the numerous complexities of these liquid desiccant systems, existing designs are not conducive to aerospace applications. Many of the complexities of these systems stem from the fact that liquid desiccants are liquids that inherently need to be sprayed and therefore require control of the flow and droplet shape.

[0157] 4.2.4 Description of the proposed approach: Solid-state ionogel condenser

[0158] The disclosed examples combine the benefits of liquid desiccant systems with the simplicity of solid-state systems. It is envisioned that a solid-state high-surface-area ionogel condenser in contact with a liquid desiccant can provide moisture removal, dehumidification, and temperature control in a small and simple package. The proposed solution will enable lighter and more maneuverable aircraft and provide superior air delivery for pilot performance and aircraft longevity. The key to the disclosed approach is the development of spherical ionogel condensers (Figure 30, right) that are droplet-like and have a high surface area for rapid heat and mass transfer. Thus, the disclosed approach has an apparent similarity to conventional spray liquid desiccant systems in that moist air flows over the spherical desiccant, except that in the disclosed case, the captured water is directly transported to a surrounding reservoir. The gel itself can be a polymer network (e.g., polyacrylamide) swollen with a liquid desiccant solution. Since the liquid solution can occupy most of the volume, the gel can have thermophysical properties similar to those of the liquid itself. However, unlike the liquid solution, the gel can mechanically behave as a soft solid, thus enabling it to maintain its spherical shape. Preliminary results show that the dehumidification achieved with liquid desiccants is indeed applicable to ionogels. In the laboratory, ionogels equilibrated with lithium chloride solution have been prepared and the dehumidification and resulting water capture over a period of time have been demonstrated, as Figure 31 shown.

[0159] Table 3: Overview of the characteristics of the proposed approach compared to existing approaches

[0160]

[0161] 4.3.1 Hydrogels and Ionogels

[0162] Hydrogels are polymeric materials with a polymeric network backbone that can be swollen with water many times its dry volume

[13] . Hydrogels are used in a variety of applications ranging from agriculture to biomedicine. Recently, hydrogels have been explored for water collection applications that rely on the same physical principle of dehumidification [14 - 16]. Since swollen hydrogels are composed mainly of water, they should have thermophysical properties (density, thermal conductivity, specific heat) almost identical to those of water. However, unlike water, hydrogels behave like elastic or viscoelastic solids

[17] . By including crosslinks within the polymer matrix, solid-like behavior can be achieved. The higher the crosslink density, the higher the mechanical stiffness. As previously studied by PI

[18] , hydrogels have a mechanical stiffness defined by the elastic volume modulus K, where

[0163]

[0164] V is the volume of the gel, p is the internal pore pressure inside the gel (as a porous medium), and π is the osmotic pressure. As the internal pore pressure inside the gel increases (more swelling), the volume also increases. At the same time, a more swollen hydrogel has a lower concentration of monomer units, resulting in a lower osmotic pressure. The degree of swelling is represented by the volume strain term s, where

[0165]

[0166] and ΔV is the volume change due purely to swelling (not stress). Combining equations 2 and 3, it is found that

[0167]

[0168] That is, the change in pressure is related to the change in volume strain.

[0169] On the other hand, an ionogel is a hydrogel equilibrated in a salt solution [15, 16, 19]. Thus, an ionogel has salts embedded within it. Given that salts increase the osmotic pressure, the ionogel shrinks from its salt-free state, pure water state.

[0170] 4.3.2 Multifunctional ionogel sphere design and transport within the gel

[0171] Dehumidification and moisture removal involve an osmotic process: the interaction between stiffness, water transport, and salt diffusion. Water is transported through the hydrogel either through the polymer network itself (pore size approximately 10 nm - 100 nm) or through larger pores (approximately 1 μm - 100 μm) created by post-synthesis treatment. Through this transport, the absorbed water from dehumidification moves through the material like a sponge, as shown in Figure 32. Within the gel, the driving force for transport is the osmotic pressure gradient, which arises from the chemical potential difference. Similarly, through the poroelastic relationship, this osmotic pressure gradient is converted into a mechanical pressure gradient in a typical porous medium flow problem.

[0172] To understand the performance of the ionogel material system, it is necessary to model the transport of several key components within the gel:

[0173] 1. The flow (velocity field) of the liquid desiccant solution swollen within the poroelastic gel

[0174] 2. The salt concentration in the liquid solution (concentration field)

[0175] 3. The thermal energy within the gel (temperature field)

[0176] Using Darcy's porous medium flow law and equation 4, the apparent velocity u (flux of volume flow) is related to the gradient of the volume strain field ε s by:

[0177]

[0178] where κ is the absolute permeability and μ is the viscosity of the flowing solution. That is, the liquid solution flows from a high volume strain εs (high swelling region) to a low volume strain. At steady state, the conservation of the liquid desiccant solution results in the divergence of the apparent flow being zero:

[0179]

[0180] Solving Equation 6 with appropriate boundary conditions yields the volume strain field due to swelling, or the so-called swelling field. The boundary conditions can be applied as long as the swelling state is known to vary with relative humidity, which can be experimentally measured. At the same time, elasticity theory can be used to determine the total strain tensor field ε, where the strain is defined to have separate stress-induced and swelling-induced components.

[0181]

[0182] Knowledge of the strain tensor field enables us to determine the deformation of the gel and any critical stress points in the gel.

[0183] Salts in the liquid can be transported from the apparent liquid velocity via advection and diffusion through the effective diffusion coefficient D 有效 of the porous medium.

[0184]

[0185] Here, appropriate boundary conditions are applied based on the relative humidity of the air. Using standard finite element method (FEM) techniques, Equations 6 - 8 can be easily solved, as Figure 33 shown.

[0186] It is envisioned that at high water fluxes, the swelling of the spheres may be higher. Preliminary analysis and simulation of the above governing equations confirm this expectation, as Figure 33 shown. Here, three different humidities near 50% equilibrium humidity are simulated. When the air is below the equilibrium humidity, the gel spheres shrink and water evaporates into the vapor region, thus humidifying the dry air. When the air is above the equilibrium humidity, the gel spheres swell and water condenses from the vapor region, thus dehumidifying the air. This two-way effect illustrates the inherent multifunctional, self-regulating behavior of this gel. In addition, the water transport rate is proportional to the difference between the equilibrium humidity and the incoming humidity; thus, the system can transport water faster when conditions require, which represents the autonomous control of the system.

[0187] Preliminary analysis shows that the combination of permeability, viscosity, bulk modulus, and diffusivity provides an insightful figure of merit representing the water transport speed. Through dimensional analysis, the following dimensionless Π groups are obtained:

[0188]

[0189] Here, Π is the relative permeability of the gel. In preliminary simulations, Π was modified, and it was confirmed that gels with higher permeability achieve higher water throughput, thus improving the humidification / dehumidification performance. It is envisioned that an ideal gel for water transport could be permeable (Task 1a, 2) and mechanically rigid (Task 1b, 2). Therefore, to optimize humidity regulation, gels with high permeability can be produced by including large pore channels for flow, and gels with high stiffness can be produced by including a large amount of crosslinking.

[0190] To effectively remove moisture (small water droplets in air) from the air stream, the ionogel condenser array can act as a filtration trap. Therefore, ionogel spheres can be designed to occupy a large cross-sectional area fraction of the air flow channel and incorporate tortuosity in the air flow channel to maximize the probability of collision between the droplets in the air and the ionogel sphere condensers. Of course, this results in relatively large ionogel spheres. However, the larger the ionogel spheres, the greater the transport resistance. Therefore, it is envisioned that optimization of the gel size, distribution / spacing, and air channel geometry needs to be performed to maximize both moisture removal and dehumidification performance simultaneously (Task 3). Once the droplets in the air are trapped, it is necessary to know how fast they are absorbed into the material. It is envisioned that the contact angle between the water droplets and the ionogel material can determine the water droplet-gel interface area and the resulting absorption rate during moisture removal (Task 1c).

[0191] Finally, to effectively control the temperature of the air stream, the ionogel sphere condenser array must act as a high-surface-area finned heat exchanger between the liquid desiccant and the air. To solve this heat transfer problem, the temperature field within the gel must be known. For this purpose, the standard convective heat equation in the steady state can be invoked, where

[0192]

[0193] where U is the same apparent velocity as before. Here, the thermophysical properties are expressed in terms of effective (composite) density, specific heat, and thermal conductivity. Given the high swelling, it is envisioned that these thermophysical properties can be similar to those of the liquid desiccant (Task 1d).

[0194] 4.4 Research Plan

[0195] To explore the proposed multifunctional ionogel concept technology, three objectives and various tasks associated with these objectives can be completed.

[0196] 4.4.1 Objective 1: Synthesize and optimize the material properties of ionogel materials

[0197] It is envisioned that Π must be maximized to optimize water throughput. Thus, wicking (the combination of wetting and porous media flow) performance can be improved and can include the introduction of micron-scale pores that significantly increase flow permeability - features detectable using a scanning electron microscope (SEM). A custom-built permeation cell can allow the characterization of the permeability of various gels.

[0198] Task 1b: Optimize stiffness. To optimize mechanical stiffness, crosslinking can be incorporated into the hydrogel. Based on preliminary results for polyacrylamide-based hydrogels, it appears that crosslinking with N,N'-methylenebisacrylamide can produce the maximum stiffness at a mixture molar concentration of 3%. It has been found that the binding of salt causes the gel to shrink and stiffen in a highly non-linear manner - a behavior that can be characterized in further detail. Stiffness, or in particular the bulk modulus, can be measured using a custom-built indentation testing machine, as Figure 34 shown in b. In the case of a custom-built humidity chamber ( Figure 34 c) controlled by a piezo-actuated air microfluidic pore opener (Elveflow), the gel can reach equilibrium under any humidity condition.

[0199] Task 1c: Optimize wettability. To optimize the wettability of the water removal performance, the contact angles of a series of gel materials can be measured. Using a custom-built goniometer, the contact angles of hydrogels in various swollen states can be measured ( Figure 11 d). It is envisioned that gels with low contact angles can absorb water more quickly. This absorption rate can be quantified through custom imaging and image processing.

[0200] Task 1d: Characterize thermophysical properties. To understand how an ion gel condenser can perform as a heat exchanger, the thermal conductivity, heat capacity, and density can be measured at different states of ion gel swelling, salt concentration, and relative humidity. Custom temperature sensing and standard wet laboratory equipment can perform these measurements. The heat capacity can be measured by differential scanning calorimetry (DSC).

[0201] 2.4.2 Objective 2: Model and simulate water, salt, and heat transport in ion gel materials. After understanding the basic system design, the key transport limitations in the device can be studied, and the results of the analysis can be fed into a larger optimization scheme.

[0202] Task 2a: Simulate transport. To provide an initial analysis of important transport issues, FEM simulations can be modeled and executed to solve for flow, stress / strain, salt concentration, and temperature (Equations 6, 7, 8, 10). Preliminary analysis indicates that the dimensionless variable Π determines transport. Further exploration and simulation can allow us to identify key geometric parameters to inform the optimal sphere design. The FEM simulation can be extended to full 3D transient space to identify any further complexities in the real system. The process of the FEM simulation for this preliminary analysis is asFigure 12 as shown

[0203] Task 2b: Validate the model through experiments. By performing selective validation experiments on individual ion gel spheres, the model and simulations can be verified with experimental data. In an iterative manner, the model can start from simple assumptions and add complexities such as strain-dependent stiffness when necessary.

[0204] 2.4.3 Objective 3: Fabricate and optimize ion gel condensers in a sphere array

[0205] Task 3a: Fabrication of a planar gel array. To fabricate a planar array of spherical gels, 3D printing can form a substrate through which an ion gel with embedded flow channels as shown Figure 33 can be extruded. Figure 36 A preliminary demonstration of this fabrication concept is shown. This simplified planar geometry allows us to test various process parameters to adjust the synthesis and fabrication recipe.

[0206] Task 3b: Optimization of the gel array tube. To optimize the water removal, dehumidification, and heat exchange performance, a simple tube with embedded ion gel spheres can be modeled (similar to Figure 30). Assuming fully developed flow through rough pipes and heat fin-like behavior, simplified heat and mass transfer equations can be established. Water removal can be modeled using Monte Carlo simulations. This modeled understanding can be verified with experimental data from prefabricated gel condenser tubes that are constructed and designed based on the insights obtained from the previous tasks.

[0207] Example 5:

[0208] Given the increasing global water shortage, there is an urgent need for atmospheric water collection. Current adsorbent-based devices that cycle between water capture and release have a low collection rate. This disclosure envisions a distinct multi-material architecture with separate and simultaneous capture and release. In this way, a proven rapid release mechanism approaching the theoretical limit can be incorporated; however, there is no capture mechanism to provide sufficient liquid for release. Inspired by tree frogs and air plants, the disclosed capture method transports water through a hydrogel membrane "skin" to a liquid desiccant. This disclosure reports an extremely high capture rate of 5.50 kg m -2 d -1 at a low humidity of 35%, limited by air-to-device convection. At higher humidities, this disclosure demonstrates up to 16.9 kg m -2 d -1 , exceeding the theoretical release limit. Simulated performance of a hypothetical one-square-meter device shows that in a dry environment, it can supply water to two to three people. This work is an important step towards providing new resources to water-scarce regions.

[0209] Bio-inspired designs for leveraging proven high-throughput release mechanisms

[0210] In contrast to monolithic single-material approaches, a multi-material approach is disclosed where capture, storage, and release are separated into individually optimized materials. The disclosed approach is inspired by nature, where soft membranes (e.g., the skin of a tree frog (14) or the cuticle of a Tillandsia plant (15); Figure 37 e) can continuously capture water from the air for hydration (47). These membranes that surround the extracellular fluid and act as a protective barrier for the organism are permeable to water and facilitate water transport (48). At the same time, the membrane-enclosed extracellular fluid stores the water required for proper hydration and survival (49). It also acts as a chemical potential reservoir that generates the driving force for inhaling water from the air through the skin / cuticle into the fluid (capture). As long as the chemical potential of the extracellular fluid is lower than that of the ambient water vapor, the organism can undergo a hydration reaction from the air. In the disclosed approach, this transport-storage separation natural design is mimicked by having separate transport-optimized capture membranes and liquid desiccants to provide the chemical potential driving force and liquid storage( Figure 37 c, d boxes).

[0211] Leveraging bio-inspired material separation principles, the present disclosure envisions a vertically integrated stacked design where the release mechanism at the top and the capture membrane at the bottom surround a gap storage basin for the liquid desiccant( Figure 37 c, d). Placing the release membrane above the liquid desiccant (ionic solution) enables the incorporation of proven high-yield solar release techniques (16 - 23) that rely on thermal localization on top of the liquid phase. The highest-performing approach utilizes a hydrogel membrane, which has been reported to have a water flux as high as 3.64 kg m-2 h-1 under full irradiation (21 - 23). Therefore, there is no need to develop new release technologies as many proven technologies have been well-established. Instead, the goal of the research is to develop capture and storage approaches that can meet or exceed the solar limit in order to adequately supply water to existing release technologies, which can later be integrated into a complete AWH system.

[0212] Recognizing this need, the focus of the present disclosure is to achieve the highest water flux through the disclosed AWH capture and storage mode of material separation. In the disclosed mode, water vapor condenses and permeates through a transport-optimized hydrogel membrane into a liquid desiccant. This desiccant is a saturated lithium bromide (LiBr) salt solution, because at typical ambient temperatures, its equilibrium relative humidity is approximately 6% to 8% (50) (Section 1A of the SI). Thus, the saturated LiBr solution is capable of capturing water vapor from the environment until this low humidity range of <10%, which is lower than other strong desiccant salts such as lithium chloride and sodium hydroxide. The LiBr solution also has an extremely high uptake rate, comparable to that of leading hydrogel-based adsorbents that have been calculated (45, 51). Biological fouling is typically a problem with membranes; however, the extreme salinity of the saturated LiBr solution surely prevents microbial growth (52). Additionally, lithium is a known microbial inhibitor (53); thus, it is reasonable to assume that biological fouling is not a problem because the highest possible concentration of lithium is applied in the liquid desiccant. Below this solution, a hydrogel membrane "skin" is used to condense and permeate water from the environment into the solution. Importantly, in stark contrast to other hydrogel-based AWH technologies (51, 54 - 57), this hydrogel membrane does not store water - it only serves as a transport medium. Thus, the water uptake characteristics of the disclosed gel membrane are somewhat independent of the water capture performance, because the liquid desiccant provides the capture driving force and storage. In any case, the water absorption / water uptake characteristics of the disclosed gel and liquid desiccant can be provided. Polyacrylamide hydrogel membranes are used because their properties can be tuned to provide several benefits. The hydrogel (permeable to solution through its nanoporous polymer network (58)) is used as an extension of the liquid desiccant by bringing it into contact with ambient air. The hydrogel is also a solid material that provides protection against particulate matter and mechanical properties that are tuned to provide flexibility and strength. The high strength of the membrane allows a large amount of liquid desiccant to be stored above it with an extremely thin membrane (0.03 mm to 0.7 mm) to optimize transport. Additionally, another motivation for using the membrane is that it serves as a physical barrier for the liquid desiccant. The membrane is porous at a polymer grid scale of approximately 10 nm, which can block any dust or physical contaminants and extend the lifespan of the liquid desiccant. As Figure 1 c, Figure 1 as shown in d, water vapor flows from the environment in the direction of lower vapor pressure to the gel-air interface and then through the hydrogel membrane into the solution chamber. In the envisioned complete AWH device, this solution will then be released through an existing solar-powered release mechanism, locally heated, and condensed into fresh liquid water (second-generation device, Figure 1c). It should be noted that any local heating requires providing thermal separation from the capture membrane and most of the liquid desiccant solution to maintain high capture performance - which can be easily achieved by using thermally insulating but permeable materials (e.g., fabric insulation, foam, aerogel, etc.). This device does not cycle in a typical way because capture and release can occur independently and simultaneously.

[0213] Reducing mass transfer resistance

[0214] To analyze and develop rapid capture and storage technologies, circuit analogies are used to understand water transport. As Figure 37 shown in Fig. f, the mass flow rate of water, ṁ (kg d -1 ) is analogous to electric current. The driving force "voltage" can be represented by the relative humidity difference, RH 环境 -RH 溶液 between the ambient and the liquid desiccant solution. Finally, the overall flow "resistance" consists of three resistors in series: the convective resistance, R 蒸气 , in the gas phase, the liquid diffusion resistance, R 凝胶 , within the gel membrane, and the convective resistance, R 溶液 , in the liquid solution. Therefore, to maximize the water capture and storage rates, the "voltage" difference of RH 溶液 should be maximized by ensuring that the solution is as saturated with LiBr as possible to reduce RH 环境 -RH 溶液 , and the resistance of R 蒸气 +R 凝胶 +R 溶液 should be minimized as much as possible. To this end, these resistances are modeled and ways to minimize the resistance are determined.

[0215] The convective resistance in the vapor resistance can be directly calculated using the Blausius solution for flow over a flat plate (59) (section 2 of SI). As a result, the water flux is proportional to the square root of the cross-flow air velocity, U, and the relative humidity difference, RHambient - RHsurface, between the ambient and the gel - air interface surface, as described by the following circuit equation:

[0216]

[0217] Here, A is the surface area of the gel membrane, D 水，空气 is the binary molecular diffusion coefficient of water vapor in air, M H2O is the molar mass of water, P 饱和 is the saturation pressure of water, μ 空气 is the dynamic viscosity of air, ρ 空气 is the air density, W is the width of the membrane along the air flow direction (38 mm for the prototype), R is the molar gas constant, and T is the absolute temperature. The convective resistance is

[0218]

[0219] To minimize R 蒸气 , the ratio of wind speed to width should be as large as possible. According to boundary layer theory, since the boundary layer thickness is proportional to W / U, the results indicate that the convective resistance is proportional to the boundary layer thickness. Therefore, placing the membrane in a windy location or using forced convection to minimize the boundary layer thickness should increase water capture and storage yields.

[0220] It should be noted that this convective resistance will be present in any atmospheric water harvesting device that uses vapor condensation. This is because water vapor ultimately originates from the air and needs to convect to a surface of the AWH device in order to be captured. Therefore, the fastest possible AWH device is one in which all subsequent resistances after R 蒸气 are negligible. The goal of this study is to develop a capture membrane with a resistance R 凝胶 that is at least one order of magnitude smaller than R 蒸气 so as to be negligible.

[0221] To develop a membrane with negligible resistance, an expression for R 凝胶 can first be derived to understand how material design parameters affect transport behavior. Here, the present disclosure builds on previous work on the mechanical stiffness, hydraulic permeability, and relative humidity dependence of crosslinked hydrogels (58, 60) based on semi-dilute polymer theory (61). A hydrogel is a nanoporous network composed of crosslinked polymer chains, where the "pores" are the spacing between the chains, which can be described as the mesh size ξ. Through any porous medium, the mass flow of water is determined by Darcy's law:

[0222]

[0223] where ρ l is the density of liquid water, κ is the hydraulic permeability, μ l is the dynamic viscosity in liquid water, and VP is the pressure gradient (≈ -ΔP / L, where L is the thickness of the membrane). Since a hydrogel is a poroelastic material, the stiffness (bulk modulus) K of the hydrogel is related to changes in pressure and volume such that K = V dP / dV (60). Defining the packing fraction s ≡ V / V 湿润 as the volume of the hydrogel in its wet state, the 100%-RH volume, the change in pressure can be expressed as

[0224]

[0225] Here, for a highly deswollen gel, s can approach zero and equals one at equilibrium in pure water. According to this packing fraction, Darcy's law can be expressed as

[0226]

[0227] where \(V_s\approx-\Delta s / L\) is the gradient of the packing fraction, such that water moves from regions of high packing fraction to regions of low packing fraction. Note also that \(\kappa K / \mu\) l is known as the poroelastic diffusion coefficient \((62,63)\) and describes the rate of diffusion of water through the poroelastic medium. In previous studies \((60)\), it has been determined that the packing fraction varies according to the relative humidity \(s\) (related to the sorption isotherm) and can be experimentally measured using a vapor sorption analyzer. Expressing the gradient of the packing fraction in terms of its dependence on humidity gives the following circuit equation for the water flow “current”:

[0228]

[0229] Thus, the corresponding resistance \(R\) within the gel film 凝胶 is

[0230]

[0231] However, this equation depends on properties that vary according to humidity. That is, the stiffness \(K\), the permeability \(\kappa\), and the thickness \(L\) vary with the packing fraction \(s(RH)\), which varies according to humidity. As previously explored in detail \((58)\), the permeability scales as \(\kappa=\kappa\) 湿润 \(s\) 2 , where \(\kappa\) 湿润 is the experimentally measurable wet value. In addition, the stiffness scales as \(K = K\) 湿润 \(s^{-9 / 4}\), where \(K\) 湿润 is the experimentally measurable wet bulk modulus \((60)\). Finally, it can be shown that for a deswelling hydrogel with a Poisson's ratio of \(1 / 3\) \((64–66)\), when constrained to a constant area \(A\), the thickness of the gel film is \(L = L\) 湿润 \(s\) 4 / 3 . All other parameters do not vary with humidity. Thus, incorporating all humidity dependencies into the gel resistance expression Equation 8,

[0232]

[0233] According to Equation 9, it can be seen that the wet permeability and stiffness should be maximized, while the thickness should be minimized. In addition, due to the \(s\) 31 / 12 factor, highly swellable gels (such that \(s\) is very small under operating conditions) will also minimize \(R\) 凝胶 . Note that in the disclosed \(R\) 凝胶In the expression, the homogeneous properties within the gel film are assumed. This is valid as long as the poroelastic Peclet number is less than one, as proven in Section 4 of the SI. Again, it is emphasized that the gel film does not act as a storage medium; thus, the water uptake rate of the gel itself is not important in determining storage performance - rather, storage is provided by the desiccant solution, which has a water uptake rate similar to that of leading hydrogel-based sorbents (45, 51). Here, the packing fraction s is used as a convenient gel property to describe its thermodynamic state, rather than as a measure of water capture performance.

[0234] Based on the analysis of the gel mass transfer resistance, an attempt was made to synthesize hydrogels with very strong type II or type III isotherm behavior to minimize the packing fraction s. Therefore, polyacrylamide hydrogels were used because they are known to have strong type II isotherm behavior (67) and a small s at low RH, as confirmed in previous (60) and current work. To prepare thin gels of 0.03 mm, insights from a recent study on highly entangled polymer networks using the minimum amount of crosslinker were utilized to enhance the hydrogels (68) (Section 1B of the SI). According to their analysis, hydrogels with entanglement greatly exceeding crosslinking have higher toughness, strength, and fatigue resistance compared to traditional crosslinking-dominated hydrogels.

[0235] The gel has a wet-state bulk modulus K 湿润 = 27.6 ± 0.2 kPa, and a maximum strain of approximately 160% to 200%. When confined to a fixed area and exposed to a saturated LiBr environment, the thickness of the gel film is approximately L = 0.03 mm. When supported by a metal grid, these films can withstand the compressive stress associated with approximately 10 cm of liquid desiccant above, equivalent to ρgh = 1.4 kPa, which is much less than the compressive strength of the material. The hydraulic permeability of the gel was measured using a custom flow cell (58) to be κwet = 7.2 x 10 -18 m 2 . Through the comprehensive experimental characterization of the synthesized gel, the gel resistance Rgel = 0.21 x 10 6 s kg -1 . Compared with the vapor resistance of Rvapor = 1.84 x 10 6 s kg -1 , assuming an ambient temperature of 23 °C and a cross-flow velocity of 0.3 m s -1 , Rgel is approximately one order of magnitude lower than R 蒸气 . Therefore, the resistance of the disclosed gel film is expected to be negligible. In addition, the resistance in the solution phase was calculated to be Rsolution = 0.093 x 10 6 s kg -1。Due to Rayleigh–Bénard mixing of the low-density, low-salt-concentration liquid at the gel–solution interface, this resistance is very low (R 溶液 is calculated in section 7 of the SI). Since R 溶液 is at least an order of magnitude lower than R 蒸气 , it is also negligible. Thus, mass transfer during the capture phase should be vapor-convection-limited – neither gel-diffusion-limited nor solution-convection-limited, where since R 凝胶 ≪ R 蒸气 . Convection-limited water capture fluxes at different air velocities and humidities were modeled at 23 °C (laboratory conditions).

[0236] Results

[0237] Laboratory tests of convection-limited capture (indoors)

[0238] To test the expectation of convection-limited behavior, 12 independent indoor capture / storage tests were performed under varying conditions of cross-flow wind speeds from 0.3 m s -1 to 0.9 m s -1 and humidities from 10% to 60% (section 1D of the SI; Figure 2 experimental results are plotted in c). To facilitate analysis and comparison with established hydrodynamic models, a wind tunnel was designed to provide laminar flow (section 1C of the SI). In the case where the gel resistance is negligible, the mass flow rate is , where R 蒸气 can be determined ab initio to predict the flow rate according to equation 2 ( Figure 38 dashed line in c), where RH 表面 = RH 溶液 . The change in the volume of the liquid desiccant ΔV was determined by photography and image processing. This volume change was converted to the mass of water captured m 捕获 (section 1E of the SI). The experimental capture rate was compared with the predicted capture rate of the Blausius convection exact solution (section 2 of the SI) and found to be in very close agreement with the unfitted results, confirming the convection-limited behavior. As shown in the graph, the water capture rate increases linearly with the ambient relative humidity. Additionally, the rate increases with the square root of the wind speed U, as expected from equation 2. Since the boundary layer will become very thin, turbulent airflow can provide further enhancement.

[0239] Outdoor water capture results (outdoors)

[0240] To demonstrate the potential of the disclosed AWH approach in arid environments, outdoor capture tests were conducted locally in Las Vegas (the metropolitan area with the lowest rainfall in the United States), where the ambient humidity was 20% to 40% in late November. Each outdoor test ran continuously for at least 24 h, and the ambient temperature and humidity changes were recorded, as Figure 39 shown. Sensor readings regarding temperature and humidity were compared with weather data from the nearby KLAS airport obtained from Wolfram Research (69), and it was confirmed that the measurements of the surrounding environment during the outdoor tests were reliable. Relying solely on natural wind flowing over the gel film, an average capture rate of 1.99 kg m-2 d -1 was measured over a 24-h period at an average RH of 25% ( Figure 39 (b), red). Notably, positive water capture was recorded even when the humidity dropped below 10% ( Figure 39 (c)), indicating water capture at the lowest relative humidity compared to other approaches ( Figure 37 (c)). Based on the insights derived from Equation 3, where mass transfer is inversely proportional to the boundary layer thickness, a small 1.4-W fan was incorporated to impose forced convection on the membrane (Figure 30(a)). At 35%, the water capture and storage yield increased to 5.50 kg m-2 d -1 , representing the highest water yield of any AWH approach at any humidity. Note that the purpose of adding the fan was to demonstrate the convective-limited transport behavior rather than a technical feature.

[0241] Further implications

[0242] Both laboratory and outdoor test results confirmed that through the disclosed bio-inspired design, water can be captured at relative humidities as low as approximately 10% and at higher humidities at rates approaching the solar limit of water release. Faster rates can be achieved at higher humidities, and a high of 16.9 kg m -2d-1 has been recorded at 57% RH. Faster rates can also be achieved with more convection. Using the 2021 Las Vegas weather data, the performance of the AWH capture device using experimentally validated Equation 2 was modeled. As Figure 40 (a) shows, the simulated annual capture rates of the AWH capture device with and without a fan (blue and red, respectively) in 2021 were determined. Relying solely on natural wind (current setting), a capture rate of 6.6 kg m -2d-1 (annual average) was modeled, which is a capture rate of 7.5 kg m -2 d -188% of the solar limit. Doubling the wind speed by forced convection or placing the device in a windy area (e.g., higher altitudes or narrow spaces between buildings) modeled the capture rate of 9.3 kg m -2 d -1 which is 124% of the solar limit. In any case, coupling the disclosed capture method with proven release techniques will achieve a complete AWH package with performance close to the solar limit. In the driest city in the United States, Las Vegas, a hypothetical one-square-meter device with a width of W = 38 mm (identical to the disclosed prototype) could provide potable water for two to three people (3 kg d -1 (36)). Note that any future scaling up of this device will require incorporating a release mechanism and considering an appropriate mechanical frame design to distribute the hydraulic stress over a large area of the gel membrane.

[0243] Assuming an appropriate release mechanism is combined with the disclosed capture and storage methods to form a complete AWH device, the global convective-limited water capture potential of the disclosed design was simulated based on a global weather dataset of temperature, humidity, and wind speed (70,71), as Figure 40 (b) shows. In almost all land areas, the water flux is greater than 10 kg m -2 d -1 . Simulating the performance of the disclosed device globally ( Figure 40 (c), blue area) results in a water flux range that generally far exceeds the performance curve required by Lord to provide safely managed drinking water for 1 billion people (8)( Figure 40 (c), green line). In fact, the convective-limited flux can exceed the single-stage solar limit and even approach the thermodynamic solar limit of the distillation process (33). Additionally, the unwanted AWH approach has potentially significant economic advantages - it is estimated that, considering only the raw material costs for bulk purchases and the total dry mass of the LiBr salt and the hydrogel membrane, the cost of the capture and storage materials is approximately $17 m -2 or $1 kg -1 . Thus, if the release mechanism is equally affordable, high-yield, convective-limited atmospheric water harvesting is highly feasible and has the potential to be developed at low cost for large-scale implementation. Complications that may arise due to scaling up (e.g., turbulence, large membrane manufacturing) can be addressed. A complete AWH system can be achieved by incorporating a release mechanism.

[0244] In summary, the present disclosure reimagines the atmospheric water collection process and envisions a new multi-layer architecture similar to the functions of skin and cutin in nature. Through this architecture, the capture, storage, and release of water can be separated into individually optimized materials. The architecture also employs a proven and highly efficient water release technology with single-stage distillation performance approaching the solar limit (21–23). To provide sufficient water to the release stage, the present disclosure focuses on the capture and storage stages and has developed a hydrogel membrane “skin” combined with a liquid desiccant. Through detailed transport and material analysis, the membrane is designed to provide the fastest possible water capture rate under the constraints of the ambient air flow of the device. This can be achieved by using a high-strength, highly entangled polymer network, making the gel extremely thin. Detailed laboratory and outdoor tests show that the disclosed device has the highest capture flux and the largest operating humidity compared to the prior art. The global impact of this convection-limited performance has been modeled, and it has been found that even in the driest environments, a hypothetical one-square-meter device can provide the daily water demand for several individuals. Using the criteria developed from the previous analysis by Lord et al. (8), implementing devices with limited convective performance in areas without secure managed drinking water can supply water to more than one billion people. The disclosed work may be an important step towards building scalable and affordable AWH devices that can provide additional water security for dry communities with reduced water supply or communities with limited infrastructure.

[0245] Method

[0246] Synthesis of hydrogel

[0247] First, a mixture of acrylamide monomer, photoinitiator (Irgacure 2959), and crosslinker (N,N’-methylenebis(acrylamide)) was made into a solution and poured into a mold with a thickness of 0.5 mm. UV irradiation was applied for 1 h. The crosslinked hydrogel samples were carefully removed from the mold and rinsed to remove unreacted chemicals. Before use, all samples were immersed in DI water for 3 days until they reached the equilibrium wet state.

[0248] Saturated salt solution

[0249] According to Greenspan (50) (Section 1A of the SI), the equilibrium relative humidity of a saturated lithium bromide (LiBr) solution at room temperature is approximately 8%. To prepare a saturated LiBr solution, LiBr salt was gradually added to DI water and mixed with a magnetic stirrer until a solid phase precipitated. After natural exothermic heating during the dissolution process, the liquid was cooled.

[0250] Tensile test

[0251] Previously, a custom-built tensile / compressive tester (60) was used to stretch six dog-bone-shaped hydrogel samples. According to the stress-strain curve, the bulk modulus K 湿润 was determined from the Young's modulus, assuming a Poisson's ratio of 1 / 3 (64 - 66). To ensure that the hydrogel samples were tested in their wet state, all tests were completed within 5 min after removal from water.

[0252] Permeability test

[0253] The hydraulic permeability κ of the hydrogel film 湿润 was measured using a custom-built permeability tester previously (58). In previous work, it was found that when ΔP / K 湿润 was in the range of 0.5 - 1, the volumetric flow rate Q was linearly related to ΔP within ±2%; therefore, the Elveflow microfluidic flow controller applied a pressure ΔP = 70%K 湿润 , and the real-time water volumetric flow rate was recorded for 30 min to calculate the hydraulic permeability of the sample based on Darcy's law.

[0254] Indoor capture and storage test

[0255] A custom-built wind tunnel was used, with its humidity PID controlled in the range of 10% to 60%, and the average velocity varying from 0.3 m s -1 to 0.9 m s -1 . The airflow consideration in the wind tunnel is shown in Section 1C of the SI. The camera took pictures of the height of the liquid meniscus every 30 s, enabling us to determine the change in the saturated solution in the chamber V 改变 , and calculate the water capture rate varying with time. The solution humidity was monitored to ensure that it remained at about 8% throughout the test.

[0256] Calculation of the captured water mass

[0257] Since the LiBr solution in the chamber remained saturated, the volume change of the liquid ΔV came from both the volume change of the saturated solution composed of the captured water and the dissolved salt, and the volume change of the undissolved salt. The mass m of the captured water 捕获 can be calculated as

[0258]

[0259] where w is the mass fraction of LiBr in water at the solubility limit, ρ 盐 is the density of the LiBr salt, and ρ 溶液 is the density of the LiBr saturated solution varying with temperature. A detailed discussion and derivation are shown in Section 1E of the SI.

[0260] Outdoor capture and storage test

[0261] The outdoor test setup was the same as the indoor setup, without a wind tunnel and humidity control system. It was tested with and without a 50 mm computer fan that consumed 1.4 W of electricity during operation. Each outdoor test was conducted continuously on the roof of the laboratory building for at least 24 h. Ambient humidity and temperature were measured and recorded throughout the experiment for analysis.

[0262] Water absorption test

[0263] Dynamic vapor sorption (DVS) was applied to determine the adsorption response of the hydrogel under varying humidity with DVS Adventure from Surface. Samples were exposed to gradually decreasing RH conditions at a 10% decrement rate, with smaller changes near the saturation point, and were allowed to reach equilibrium at each condition from 98% to 10%. The mass fraction isotherm conformed to the GAB isotherm model (67). Further details of the water adsorption tests and modeling are shown.

[0264] Collection performance benchmark curve of Lord et al.

[0265] Lord et al. (8) determined the specific yield required to provide safely managed drinking water (SMDW) for one billion people considering global data on local population distribution, local solar irradiance, local humidity, and local water demand. The humidity-dependent specific yield is expressed as kg of water produced per kW h of solar energy. In the work presented, the quantified capture or collection performance was used as the mass flux in kg m -2 d -1 units; thus, to convert the specific yield to mass flux, the specific yield was multiplied by the global horizontal irradiance (GHI), which is equivalent to the incident solar radiation on a flat surface per unit area. In Figure 1 and Figure 4 (green curve), the maxima of the two curves (linear and logistic) proposed by Lord et al. were determined, where

[0266]

[0267] and q″ 太阳能 is the global average GHI of 4.7 kW h m -2 d -1 . Thus, the conservative mass flux requirement was demonstrated to provide SMDW for one billion people.

[0268] Modeling location-specific water capture potential

[0269] The water release amount limited by global solar energy was determined using Equation 1 with global horizontal irradiance data from the Global Solar Atlas 2.0 (72). The convective-limited water capture flux potential was calculated using Equation 2, where RH表面 = RH 环境 , 假定 R 凝胶 << R 蒸气 。Diffusion coefficient D 水，空气 The value is determined using the values and equations in (73). The water and moist air properties are determined using CoolProp (74). The local wind speed data is from Wolfram Research (69), while the global wind speed data is from the Global Wind Atlas (70). The 10-m wind speed is converted to 1-m wind speed using a power-law wind profile with an exponent of 1 / 7 (75). The global humidity and temperature data are from version HadISDH.blend1.3.0.2021f of the Hadley Centre Integrated Surface Humidity Dataset of the UK Met Office (71).

[0270] Solar limit of ideal distillation

[0271] For a single-stage distillation system without heat recovery, the energy required for distilled water is the latent heat, as in Equation 1. However, in a thermodynamically reversible (100% second-law efficiency; no entropy generation) black box, when a saturated salt solution flows in, the solar thermal energy Q 水 required to produce the distilled water m 热 flow is

[0272]

[0273] where R is the molar gas constant, T 环境 is the ambient temperature, RH 饱和 is the equilibrium relative humidity of the saturated salt solution, M 水 is the molar mass of water, and T_thermal is the temperature of the heat source (assumed to be the boiling point of water at 373 K in Figure ). Note that this device inherently uses a Carnot heat engine to produce work: W = Q 热 (1 - T 环境 / T 热 ). For a solar-powered release system, where Q 热 = Q 太阳能 , the thermodynamically limited mass flux is

[0274]

[0275] where A is the area of the device, and q″ 太阳能 = Q 太阳能 / A. The full derivation is provided in SI.

[0276] References and notes

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[0353] 1. Additional Notes on Experimental Methods

[0354] The disclosed hydrogel-based atmospheric water harvesting (AWH) approach utilizes a thin hydrogel film at the bottom of a solution chamber. The saturated salt solution (LiBr) in the chamber creates a lower chemical potential, providing a driving force and capturing ambient water vapor. Separated from the water storage function, the hydrogel film serves as a permeable medium to facilitate rapid capture.

[0355] Saturated salt solution (liquid desiccant)

[0356] To create a low chemical potential environment to drive water into the liquid phase (liquid desiccant), a saturated aqueous solution of lithium bromide (LiBr) salt is used. Greenspan provided a detailed list of the relative humidities of different saturated salt solutions at varying temperatures [1]. Compared to other salts, LiBr provides the lowest equilibrium relative humidity, which will provide the greatest driving force for water capture and the greatest humidity range for possible capture. In the temperature range of 0 °C to 50 °C, the equilibrium relative humidity range of the saturated LiBr solution is 7.75 + / - 0.83% to 5.53 + / - 0.31%. The LiBr saturated solution is prepared by gradually adding the salt to DI water in an amount greater than its solubility at room temperature. During salt addition, the solution temperature increases due to the strongly exothermic dissolution associated with LiBr. Using the resulting high temperature enables us to ensure that the solution is completely saturated when finally cooled to room temperature. This is because, according to Handbook of Chemistry and Physics Online [2], the solubility of LiBr (and most salts) increases with temperature. Additionally, saturation is confirmed by precipitating the solid phase of the salt from the solution.

[0357] Hydrogel film

[0358] Polyacrylamide hydrogel (PAAm) membranes were prepared from aqueous stock solutions of the following chemicals: acrylamide (AAm, initial monomer, Merck), N,N'-methylenebis(acrylamide) (MBA, crosslinker, Sigma-Aldrich), and Irgacure 2959 (photoinitiator, Sigma Aldrich). Some important ratios were controlled during mixing: the crosslinker ratio (the ratio of the number of moles of MBA to the number of moles of AAm, 0.1%), the water ratio (the ratio of the number of moles of water to the number of moles of AAm during preparation, 11), and the initiator ratio (the ratio of the number of moles of Irgacure 2959 to the number of moles of MBA, 0.4). After all the chemicals were completely dissolved in DI water, the mixed solution was poured into a transparent mold with a fixed thickness of 0.5 mm, which was equal to the thickness of the hydrogel after synthesis. UV irradiation (365 nm, 100 W LED array) was applied 5 cm above the solution for 1 h. Then the cured sample was removed from the mold and rinsed to remove unreacted chemicals. The clean sample was immersed in DI water for 3 days until it reached an equilibrium state with a thickness of approximately 0.7 mm.

[0359] In previous work [3], the crosslinker ratio of pure PAAm hydrogels varied from 0.5% to 7%, and the stiffness (bulk modulus) was measured. It was confirmed that adding a crosslinker could increase the stiffness; however, increased brittleness was observed. Highly entangled hydrogels with low crosslinking were synthesized according to the method developed by Kim et al. [4], as highly strain gels with high fracture toughness were desired. When synthesized in a reduced water environment, such gels have a high degree of polymer chain entanglement, greatly exceeding crosslinking, thus providing high toughness, strength, and fatigue resistance. Therefore, the hydrogels were synthesized with a crosslinker ratio = 0.1% (MBA mol / AAm mol), a water ratio = 11 (DI water mol / AAm mol), and an initiator ratio = 0.4 (Irgacure mol / MBA mol). Compared with more conventional crosslinked gels (crosslinker ratio = 0.5%) with a bulk modulus of approximately 7 kPa, the bulk modulus of the disclosed highly entangled hydrogels is 28 kPa. In addition, the disclosed entangled gels have a high maximum strain of 160% to 200% at failure, ensuring that the disclosed gels can withstand high tensile forces when confined to a fixed area and swollen due to contact with a liquid desiccant. Section 3 of the SI provides details of the gel's response to tensile forces in such an environment.

[0360] Wind tunnel flow considerations

[0361] To simplify the analysis, the wind tunnel was designed to ensure laminar airflow for laboratory-controlled capture and storage tests. The Reynolds number Re of the airflow in the wind tunnel is

[0362]

[0363] where ρ 空气 is the air density (1.205 kg / m3), ρ 空气 is the dynamic viscosity of air (0.000 018 2 s Pa), U is the air flow velocity, and Dh is the hydraulic diameter of the channel. This hydraulic diameter is

[0364]

[0365] where A is the cross-sectional area of the wind tunnel and P is the perimeter of the wind tunnel (P = 2×(4 mm + 38 mm)). By inserting the values of all parameters at the maximum achievable velocity of 0.9 m s-1, the Re of the air flow was found to be 449.7 (<2300), which confirmed that the air flow in the wind tunnel was laminar. In addition, since no inlet region was introduced before the part of the wind tunnel under the gel film, the flow on a flat plate with a developing boundary layer was used to approximate the flow conditions under the gel.

[0366] Laboratory-controlled capture and storage tests in the wind tunnel

[0367] To test the hypothesis of convective-limited water mass transfer, indoor wind tunnel experiments were performed under a synthetic hydrogel film below a saturated LiBr solution in a prototype capture and storage device. The tests were performed at a room temperature of ≈23 °C. The mass flow rate was measured at different relative humidities and wind speeds (volumetric flow rate of air). It was necessary to independently control the relative humidity and air flow rate below the prototype ( Figure 38 (a)). The input air was provided by the building air supply with an RH of approximately 5%. The air flowed through a flow meter in which the volumetric flow rate Q of the air input could be adjusted to the desired value using a valve (connected to the wind tunnel), with a velocity control uncertainty of approximately ±0.07 m / s. Then, the air flow was split into two paths: in one path, the air flow remained in its dry state; in the other path, the air was humidified to nearly 99% by bubbling through three glass media bottles filled with water. 空气 Using an Arduino microcontroller programmed with a custom PID control algorithm, the ratio between the dry air flow rate and the humid air flow rate could be adjusted to achieve the desired humidity level within 1% RH. The resulting mixed air flowed under the hydrogel film through a 3D printed wind tunnel with a cross-section of 4 mm by 38 mm, where the cross-sectional area was Ahole and the flow length W through the hydrogel was 38 mm. The average wind speed was calculated as U = Q

[0368] / A 空气 / A 洞 . The top wall of the wind tunnel channel was the 38 mm by 38 mm bottom surface of the hydrogel film supported by a thin metal grid.

[0369] The camera is horizontally oriented towards the solution chamber and focused on the liquid-vapor interface of the solution to record changes in the liquid level. The change in the height of the solution surface is determined through image processing. Multiplying the height by the chamber cross-sectional area (38 mm by 38 mm) indicates the volume change ΔV (in Figure 38 (b) of Example 4), which is then converted to the mass of water captured (Section 1E of SI). Sensors are placed at the wind tunnel outlet to provide feedback to the PID humidity control system. Twelve independent indoor capture tests were performed, changing the wind speed at three values (0.3 m s -1 , 0.6 m s -1 and 0.9 m s -1 ) and the relative humidity at four values (10%, 20%, 40% and 60%).

[0370] A video showing the change in liquid volume over time at U = 0.9 m s-1 at 57% RH can be viewed in the supplementary video or at https: / / youtube.com / shorts / gomgG9pwWUQ. The speed of the video is increased by 750 times.

[0371] References

[0372] 1. L. Greenspan, “Humidity fixed points of binary saturated aqueous solutions,” J. research Natl. Bureau Standards. Sect. A, Phys. chemistry 81, 89 (1977).

[0373] 2. Chemnetbase, “Aqueous Solubility of Inorganic Compounds as a Function of Temperature Values Are in Mass% of Solute,” https: / / hbcp.chemnetbase.com / faces / documents / 05_33 / 05_33_0008.xhtml (2014).

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[0375] 4. J. Kim, G. Zhang, M. Shi, and Z. Suo, “Fracture, fatigue, and friction of polymers in which entanglements greatly outnumber cross-links,” Science 374, 212 - 216 (2021).

[0376] 5. J. M. Wimby and T. S. Berntsson, “Viscosity and density of aqueous solutions of libr, licl, znbr[sub 2], cacl[sub 2], and lino[sub 3]; 1: Single salt solutions,” J. Chem. Eng. Data; (United States) 39 (1994).

[0377] 6. T. L. Bergman, A. S. Lavine, F. P. Incropera, and D. P. DeWitt, Fundamentals of heat and mass transfer, vol. 8 (Wiley Global Education US, 2018).

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[0399] All publications and patent applications mentioned in this specification are indicative of the level of those skilled in the art to which the invention pertains. All publications and patent applications are hereby incorporated by reference to the same extent as if each individual publication or patent application was specifically and individually indicated to be incorporated by reference.

[0400] Exemplary aspects

[0401] In view of the described products, systems, and methods and their variations, certain more specifically described aspects of the invention are described hereinafter. However, these specifically elaborated aspects should not be construed as imposing any limitation on any different claims containing the different or more general teachings described herein, or that the “specific” aspects are in some way limited to a meaning different from the inherent meaning of the language literally used therein.

[0402] Aspect 1. An atmospheric water capture device for converting water vapor into liquid water, the device comprising:

[0403] A housing including an inlet configured to receive ambient atmosphere; and

[0404] A basin disposed within the housing, the basin comprising:

[0405] A first section configured to draw water from the received ambient atmosphere,

[0406] At least one channel configured to store an ionic solution and the water drawn by the first section, and

[0407] A second section configured to evaporate the water stored in the at least one channel.

[0408] Aspect 2. The device according to aspect 1, the device further comprising an outlet configured to dispense the evaporated water from the second section.

[0409] Aspect 3. The apparatus according to aspect 2, wherein the apparatus further comprises a condenser tube connected to the outlet and configured to condense the evaporated water from the outlet.

[0410] Aspect 4. The apparatus according to aspect 3, wherein the apparatus further comprises a reservoir connected to the condenser tube and configured to store the condensed water.

[0411] Aspect 5. The apparatus according to any one of the preceding aspects, wherein the apparatus further comprises an air cooling mechanism configured to cool the received ambient atmosphere.

[0412] Aspect 6. The apparatus according to any one of the preceding aspects, wherein the apparatus further comprises a heater configured to heat the second section of the basin.

[0413] Aspect 7. The apparatus according to any one of the preceding aspects, wherein the basin further comprises a thermal insulator surrounding the at least one channel.

[0414] Aspect 8. The apparatus according to any one of the preceding aspects, wherein the at least one channel comprises a porous hydrogel infused with the ionic solution.

[0415] Aspect 9. The apparatus according to any one of the preceding aspects, wherein the ionic solution is lithium bromide.

[0416] Aspect 10. The apparatus according to any one of the preceding aspects, wherein the first section comprises a capture gel.

[0417] Aspect 11. The apparatus according to any one of the preceding aspects, wherein the second section comprises an evaporation gel.

[0418] Aspect 12. The apparatus according to any one of the preceding aspects, wherein the basin is configured to distill water vapor from the received ambient atmosphere.

[0419] Aspect 13. A method comprising:

[0420] capturing atmospheric water using an atmospheric water capture device, the atmospheric water capture device comprising:

[0421] a housing comprising an inlet configured to receive ambient atmosphere; and

[0422] a basin disposed within the housing, the basin comprising:

[0423] a first section configured to draw water from the received ambient atmosphere,

[0424] At least one channel configured to store the ionic solution and the water sucked away by the first segment, and

[0425] A second segment configured to evaporate the water stored in the at least one channel.

[0426] Aspect 14. The method according to aspect 13, wherein the capturing of atmospheric water includes:

[0427] Receiving ambient atmosphere through the inlet;

[0428] Cooling the received ambient atmosphere;

[0429] Diffusing water from the received ambient atmosphere via the first segment; and

[0430] Storing the water in the at least one channel.

[0431] Aspect 15. The method according to aspect 13 or aspect 14, wherein the atmospheric water capture device further includes an outlet, and the outlet distributes the evaporated water from the second segment.

[0432] Aspect 16. The method according to aspect 15, wherein the atmospheric water capture device further includes a condenser tube connected to the outlet, and the condenser tube condenses the evaporated water from the outlet.

[0433] Aspect 17. The method according to aspect 16, wherein the atmospheric water capture device further includes a reservoir connected to the condenser tube, and the reservoir stores the condensed water.

[0434] Aspect 18. The method according to any one of aspects 13 to 17, wherein the atmospheric water capture device further includes an air cooling mechanism, and the air cooling mechanism cools the received ambient atmosphere.

[0435] Aspect 19. The method according to any one of aspects 13 to 18, wherein the atmospheric water capture device further includes a heater, and the heater heats the second side of the basin.

[0436] Aspect 20. The method according to any one of aspects 13 to 19, wherein the basin of the atmospheric water capture device further includes a thermal insulator surrounding the at least one channel.

[0437] Aspect 21. The method according to any one of aspects 13 to 20, wherein the at least one channel of the atmospheric water capture device includes a porous hydrogel infused with the ionic solution.

[0438] Aspect 22. The method according to any one of aspects 13 to 21, wherein the ionic solution is lithium bromide.

[0439] Aspect 23. The method according to any one of aspects 13 to 22, wherein the first segment includes a capture gel.

[0440] Aspect 24. The method according to any one of aspects 13 to 23, wherein the second segment includes an evaporation gel.

[0441] Aspect 25. The method according to any one of aspects 13 to 24, wherein the basin of the atmospheric water capture device distills water vapor from the received ambient atmosphere.

[0442] Aspect 26. The method according to any one of aspects 13 to 25, the method further comprising cooling the received ambient atmosphere.

[0443] Aspect 27. The method according to any one of aspects 13 to 26, the method further comprising:

[0444] heating the second side of the basin;

[0445] evaporating the water stored in the at least one channel via the second segment; and

[0446] condensing the evaporated water.

[0447] Aspect 28. The method according to aspect 27, wherein the step of diffusing water from the received ambient atmosphere and the step of condensing the evaporated water occur concurrently.

[0448] Aspect 29. The device according to any one of aspects 1 to 12, wherein the device is powered by natural solar energy.

[0449] Aspect 30. The device according to aspect 29, wherein the device does not include a power adapter.

[0450] Aspect 31. A device, comprising:

[0451] a solid-state ionic gel condenser configured to condense water vapor; and

[0452] a liquid desiccant in contact with the solid-state ionic gel condenser, the liquid desiccant being configured to capture the condensed water vapor.

[0453] Aspect 32. The device according to aspect 31, wherein the device is located inside an aircraft carrier cockpit.

[0454] Aspect 33. The apparatus according to aspect 31 or aspect 32, wherein the solid-state ion gel condenser is a hydrogel material.

[0455] Aspect 34. The apparatus according to aspect 33, wherein the hydrogel material is a water-absorbing polymer material.

[0456] Aspect 35. The apparatus according to any one of aspects 31 to 34, wherein the liquid desiccant is a salt solution.

[0457] Aspect 36. A method for condensing and capturing water vapor using the apparatus according to any one of aspects 31 to 35.

[0458] Although the foregoing invention has been described in detail by way of illustration and example for the purpose of clear understanding, certain changes and modifications may be made within the scope of the appended claims.

Claims

1. An atmospheric water capture device for converting water vapor into liquid water, the device comprising: A housing, which includes an inlet configured to receive ambient atmosphere; and A basin, which is disposed within the housing, the basin including: A first section configured to draw water from the received ambient atmosphere, At least one channel configured to store an ionic solution and the water drawn by the first section, and A second section configured to evaporate the water stored in the at least one channel.

2. The device according to claim 1, further comprising an outlet configured to distribute the evaporated water from the second section.

3. The device according to claim 2, further comprising a condensing tube connected to the outlet and configured to condense the evaporated water from the outlet.

4. The device according to claim 3, further comprising a reservoir connected to the condensing tube and configured to store the condensed water.

5. The device according to claim 1, further comprising an air cooling mechanism configured to cool the received ambient atmosphere.

6. The device according to claim 1, further comprising a heater configured to heat the second section of the basin.

7. The device according to claim 1, wherein the basin further comprises a thermal insulator surrounding the at least one channel.

8. The device according to claim 1, wherein the at least one channel comprises a porous hydrogel infused with the ionic solution.

9. The device according to claim 1, wherein the ionic solution is lithium bromide.

10. The device according to claim 1, wherein the first section comprises a capture gel.

11. The device according to claim 1, wherein the second section comprises an evaporation gel.

12. The device according to claim 1, wherein the basin is configured to distill water vapor from the received ambient atmosphere.

13. A method, comprising: Capturing atmospheric water using an atmospheric water capture device, the atmospheric water capture device including: A housing, which includes an inlet configured to receive ambient atmosphere; and A basin, which is disposed within the housing, the basin including: A first section configured to draw water from the received ambient atmosphere, At least one channel configured to store an ionic solution and the water drawn by the first section, and A second section configured to evaporate the water stored in the at least one channel.

14. The method according to claim 13, wherein said capturing atmospheric water comprises: Receiving ambient atmosphere through the inlet; Cooling the received ambient atmosphere; Diffusing water from the received ambient atmosphere via the first section; and Storing the water in the at least one channel.

15. The method according to claim 13, wherein said atmospheric water capturing device further comprises an outlet, and wherein said outlet distributes the evaporated water from said second segment.

16. The method according to claim 15, wherein said atmospheric water capturing device further comprises a condensing tube connected to said outlet, and wherein said condensing tube condenses the evaporated water from said outlet.

17. The method according to claim 16, wherein said atmospheric water capturing device further comprises a reservoir connected to said condensing tube, and wherein said reservoir stores the condensed water.

18. The method according to claim 13, wherein said atmospheric water capturing device further comprises an air cooling mechanism, and wherein said air cooling mechanism cools the received ambient atmosphere.

19. The method according to claim 13, wherein said atmospheric water capturing device further comprises a heater, and wherein said heater heats the second side of said basin.

20. The method according to claim 13, wherein said basin of said atmospheric water capturing device further comprises a thermal insulator surrounding said at least one channel.

21. The method according to claim 13, wherein said at least one channel of said atmospheric water capturing device comprises a porous hydrogel infused with said ionic solution.

22. The method according to claim 13, wherein said ionic solution is lithium bromide.

23. The method according to claim 13, wherein said first segment comprises a capturing gel.

24. The method according to claim 13, wherein said second segment comprises an evaporation gel.

25. The method according to claim 13, wherein said basin of said atmospheric water capturing device distills water vapor from the received ambient atmosphere.

26. The method according to claim 13, which further comprises cooling the received ambient atmosphere.

27. The method according to claim 13, which further comprises: Heating the second side of the basin; Evaporating the water stored in the at least one channel via the second section; and Condensing the evaporated water.

28. The method according to claim 27, wherein the step of diffusing water from the received ambient atmosphere and the step of condensing the evaporated water occur concurrently.

29. The apparatus according to any one of claims 1 to 12, wherein the apparatus is powered by natural solar energy.

30. The apparatus according to claim 29, wherein the apparatus does not include a power adapter.

31. An apparatus comprising: A solid ionic gel condenser configured to condense water vapor; and A liquid desiccant in contact with the solid ionic gel condenser, the liquid desiccant configured to capture the condensed water vapor.

32. The apparatus according to claim 31, wherein the apparatus is located within an aircraft carrier cockpit.

33. The apparatus according to claim 31, wherein the solid-state ion gel condenser is a hydrogel material.

34. The apparatus according to claim 33, wherein the hydrogel material is a water-absorbing polymer material.

35. The apparatus according to claim 31, wherein the liquid desiccant is a salt solution.

36. A method of condensing and capturing water vapor using the apparatus according to any one of claims 31 to 35.

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