Atmospheric water harvesting systems

Abstract

Atmospheric water harvesting systems, including an adsorbent heat exchanger that includes an adsorber structure. The adsorber structure comprises, in some embodiments, an array of fins coupled to one or more heat pipes, where an adsorbent material is included on the fins. In some embodiments, the system passes ambient air across the adsorber structure to adsorb water, then apples heat to the adsorber structure via a heat source and heat block coupled to the heat pipes to desorb the water. The desorbed water is passed through a condenser to capture the liquid water.

Description

ATMOSPHERIC WATER HARVESTING SYSTEMSCROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of U.S. Provisional Application No. 63 / 550,808, filed February 7, 2024 and U.S. Provisional Application No. 63 / 754,797 filed February 6, 2025, which are both incorporated by reference as if disclosed herein in their entireties.STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH AND DEVELOPMENT

[0002] This invention was made with government support under W911QY-19-1-0010 awarded by the Army / ARL, and 2139322 awarded by the National Science Foundation. The government has certain rights in the invention.FIELD

[0003] The present technology relates to atmospheric water harvesting (AWH), and more specifically, to sorption-based AWH.BACKGROUND

[0004] Over 2 billion people live in water-stressed regions with over 700 million living under high and critical water stress levels. Water stress derives from physical water scarcity and includes water access limited by socio-economic strife and contamination due to biological and chemical agents. Decentralized, reliable sources of water are needed to alleviate both water scarcity and stress concerns. One approach to this issue is AWH. AWH seeks to take advantage of the 13 trillion m3of freshwater available in the atmosphere that is accessible in all regions of the planet. Fog harvesting is the simplest form of AWH where tiny droplets of water are collected on mesh nets or other surfaces. This process is particularly attractive as fog contains water in the liquid state requiring no energy to trigger phase change (condensation), but water production is limited to saturated conditions (i.e., relative humidity (RH) = 100%). Refrigerationbased dewing (RBD) is a well-explored approach for AWH, where unsaturated ambient air (RH < 100%) is cooled below its dew point to drive water condensation. This can be achieved using vapor compression cycles (VCC), the predominant energy consumption for this process. Thetechnological maturity of VCC makes RBD-system an attractive solution for AWH, however, the specific energy consumption ^kWhm^ter is well known to drastically increase as the operational conditions become more arid. As an alternative, sorption-based AWH (SAWH) techniques may be able to operate in a wider range of conditions, including climates where RBD is infeasible.

[0005] SAWH techniques exploit physical and chemical adsorption to trap water molecules from the air. To harvest water from the atmosphere, first water vapor is allowed to saturate the sorbent material. To produce liquid water, the sorbent is heated to rapidly release the water vapor, which is then condensed to complete a single cycle. The dominant energy requirement of SAWH is the heating of the sorbent material during desorption. Improving the characteristics of the sorbent material and the process in which they are used are important to improving daily water production. For example, high water uptake will lead to more water production per cycle and sorption kinetics are important to enable multiple daily cycles, both of which increase the daily water production.

[0006] SAWH is divided into two main cycling categories, active and passive. Passive systems utilize solar thermal energy to drive desorption, electing to adsorb water at night and desorb during the day in a diurnal pattern. Water production in these systems is limited to a single daily cycle, and therefore to increase productivity (kgwaterkg~^sorbentday~1) for a given system, greater quantities of adsorbents must be used. However, sorbent materials remain the largest cost associated with AWH technology. In addition, adsorbent materials often do not require all night adsorption and could feasibly adsorb to capacity several times during a 24-hour period. Active systems may be able to operate several cycles with the addition of active heaters in place of solar thermal power.

[0007] Active heating and refrigeration have been utilized to improve AWH performance on a daily basis. As discussed above, active heating enables multiple cycles during the day but in doing so often requires condensation during periods when temperatures are elevated. Utilizing vapor compression cycles counteracts the negative effects of condensing at high ambient temperatures which will lead to a poor water yield. The theoretical maximum amount of water that can be removed from the humid airstream in a simple condenser is the water above thesaturation concentration at the condensation temperature, higher temperatures require more water for saturation. In practice the presence of non-condensable gases in the condenser will strongly impact performance, lowering the feasible yield in real systems. The significant electrical energy draw for the operation of heating elements and active refrigeration limit the application of AWH as an emergent technology.

[0008] What is needed, therefore, is AWH technology with higher reliability, higher water yield, and higher efficiency in a wide variety of atmospheric conditions.SUMMARY

[0009] Accordingly, one aspect of the present disclosure is directed to an atmospheric water harvesting system that utilizes an adsorbent heat exchanger (AHX) comprising an adsorber structure coupled to a heat block via at least one heat pipe. The heat block is configured to be heated by a heat source, for example a high-energy density fuel combustion source. In some embodiments, the adsorber structure comprises at least one fin with a metal-organic framework (MOF) adsorbent material, where the fin is coupled to the at least one heat pipe. The adsorber structure adsorbs water from the ambient air. The heat source heats the heat block and consequently the heat pipes and adsorber structure to desorb the water. The desorbed water is extracted in a condenser in some embodiments and collected in a water collection tank.

[0010] Another aspect of the present disclosure is directed to an AHX comprising at least one heat pipe and an adsorber structure with at least one fin coupled to the at least one heat pipe, the at least one fin comprising an adsorbent material. In some embodiments, the AHX comprises a plurality of heat pipes coupled to a plurality of fins, and the adsorbent material comprises an MOF material.

[0011] Some embodiments enable continuous daily cycling, using fuel as an energy source to drastically reduce the system footprint relative to a purely solar-driven system.BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Further objects, aspects, features, and embodiments of the present technology will be apparent from the drawing Figures and below description.

[0013] FIG. 1 A shows a schematic illustration of an atmospheric water harvesting system according to one embodiment of the present technology.

[0014] FIG. IB-1 shows a perspective view of components of a heat exchanger according to the embodiment of FIG. 1A.

[0015] FIG. IB-2 shows a close-up view of the area in the dashed line shown in FIG. IB-1.

[0016] FIGs. 1C shows a perspective view the heat exchanger according to the embodiment of FIG. 1A.

[0017] FIG. 2A shows a schematic illustration of an atmospheric water harvesting system operating in adsorption mode according to an embodiment of the present technology.

[0018] FIG. 2B shows a schematic illustration of an atmospheric water harvesting system operating in desorption mode according to an embodiment of the present technology.

[0019] FIG. 3A shows a side internal view of an atmospheric water harvesting system according to a second embodiment of the present technology.

[0020] FIG. 3B shows an exploded view of the embodiment of FIG. 3A.

[0021] FIG. 3C shows a schematic illustration of the system of FIG. 3A in adsorption mode.

[0022] FIG. 3D shows a schematic illustration of the system of FIG. 3 A in desorption mode.

[0023] FIG. 4A shows a perspective view of the inner components of an atmospheric water harvesting system according to an alternative embodiment of the present technology.

[0024] FIG. 4B shows a perspective exploded view of components of an AHX module according to the embodiment of FIG. 4 A.

[0025] FIG. 4C shows a perspective view of an AHX module according to the embodiment of FIG. 4 A.

[0026] FIG. 4D shows a front view of the system of FIG. 4A.DETAILED DESCRIPTION

[0027] FIG. 1A shows a schematic illustration of an AWH system 100 according to first embodiment of the present technology. In some embodiments, system 100 comprises an adsorbent heat exchanger (AHX) 101 coupled to at least one heat pipe 102. In some embodiments, the AHX comprises an adsorber structure 103 (shown in FIG. IB-1) and is configured to receive heat from a heat block 104 and to heat air within the AHX 101 and release water vapor. The system 100 further comprises a heat source 105. In some embodiments, the heat block 104 is configured to be heated by the heat source. The system 100 also comprises at least one heat pipe 102, which is coupled to the heat block 104 and the AHX 101. In the embodiment shown, the system comprises a plurality of heat pipes 102 (eight in this embodiment) coupled to the heat block and AHX. As described below, the adsorber structure receives heat from the heat block via the at least one heat pipe 102.

[0028] In some embodiments, the system 100 further comprises a condenser 106 that is coupled to the AHX. In some embodiments, the condenser 106 is coupled via a first conduit 107. In other embodiments, the condenser and AHX are integrated and / or connected differently. The condenser 106 is configured to receive the water vapor released from the AHX and to release liquid water. In some embodiments, the system 100 further comprises a water collection tank 108 coupled to the condenser. The water collection tank 108 is configured to collect the liquid water 109 released from the condenser 106. In some embodiments, the water collection tank 108 is coupled to the condenser via a second conduit 110. In other embodiments, the water collection tank and condenser are integrated and / or connected differently.

[0029] In some embodiments, such as the embodiment shown in FIG. IB-1, the adsorber structure 103 comprises at least one fin 112 coupled to the at least one heat pipe 102. As shown in FIG. IB-1 and IB-2, the adsorber structure 103 comprises a plurality of fins 1 12 wherein each fin is separated from adjacent fins by a gap 113, and each fin is coupled to at least one of the plurality of heat pipes. In the embodiment shown, the fins 112 are arranged in a block formation, where the fins are generally planar, square, and positioned parallel to each other. Other fin shapes are used in other embodiments. In the embodiment shown, 14 fins are included in the adsorber structure 103. In the embodiment shown, the gap is approximately 3.5 mm. The gaps enhance adsorption and desorption by allowing increased airflow past the adsorber structure.Differently sized gaps are used in other embodiments to accommodate different fin size and adsorbent material and thickness.

[0030] In some embodiments, each of the plurality of fins 112 comprises metal foam 114 coupled to a metal sheet 115. In the embodiment shown, each fin 112 includes two metal foam portions 114, each attached to opposite sides of the sheet 115. In some embodiments, the foam portions are pieces that are brazed to the sheet 115. In some embodiments, the metal foam 114 and the metal sheet 115 comprise copper, aluminum, or combinations thereof. In the embodiment shown, the foam 114 are copper foam pieces sized 12.7cm x 12.7cm x 0.3cm brazed to either side of a copper sheet sized 12.7cm x 12.7cm x 0.02cm. Each piece of copper foam was fabricated to have an average porosity of 95% and a ppi of 80, in this embodiment. To accommodate the heat pipes 102, each copper sheet underwent a series of hole punches to achieve the desired hole sizing and pattern in each fin. In this embodiment, each hole was 1.27 cm in diameter resulting in a tight fit with the heat pipes of the same diameter and had an extending collar of height 0.27 cm. The collar strengthened the mechanical bond between the heat pipes and the fins and improved thermal contact between them. Thermal epoxy (ThermoBond 26) was applied to these joints for additional strength. In this embodiment, a matching hole pattern was manually drilled in the foam pieces in a batch process before the joining process. The copper foam pieces were joined to the copper sheet through a vacuum brazing technique. Vacuum brazing is a brazing process done in an evacuated chamber under high heat. Evacuation of the chamber prevents oxidation and removes the requirement of flux for the brazing process. The lack of flux and a thin braze sheet (0.004 cm) prevent blockage of the foam pores near the joint leaving the maximum amount of free space to be filled by adsorbent material. In some embodiments, the fins 112 comprise aluminum sheets and aluminum foam pieces. Thus, in some embodiments, the adsorber structure fins are attached to the heating assembly via heat pipes that contact the various holes in the fin. The copper foam and sheet provide a highly thermally conductive material to promote uniform heating of the MOF during desorption and a stable substrate for scalable system design. The left side of FIG. IB-1, shows the portions of the heat pipes 102 that are coupled to the heat block, but this portion is covered by a heatshield.

[0031] In some embodiments, the metal (e.g. aluminum) sheets are coated with an adsorber coating. In some embodiments, the adsorber coating ranges in thickness from 300-500 microns and utilizes a silane organic polymer as a binder agent. Such embodiments utilize thin coatings that can lead to faster dynamics and increased productivity in terms of liters of water produced per kilogram of absorbent per day.

[0032] In some embodiments, each of the plurality of fins 112 comprises a metal sheet 115 and the adsorber coating comprises a zeolite material. In some embodiments, the metal sheet comprises aluminum and the adsorber coating comprises AQSOA Z02. In other embodiments, other types of zeolite material are used. In some embodiments, the AQSOA Z02 is applied to the metal sheets using a dip coating procedure. In some embodiments, the dip coating procedure includes two coatings that are cured after each application. For example, the first coating is done in a silane solution before any zeolite has been added and serves as a foundation for further coatings. The base solution is formed with 90% pure ethanol, 5% DI water and 5% Trimethoxy(propyl)silane. To prevent self-condensation the pH was adjusted to 4 by adding acetic acid then was left to stir at room temperature for 24 hours. In this embodiment, aluminum sheets were used as the metal sheets and were cleaned before coating in three steps. The sheets were first washed for 60 seconds in a 0.1 N NaOH solution to remove any grease from the surface. The residual alkaline solution was rinsed off using DI water and then the sheets were rinsed in acetone. The cleaned aluminum samples were dipped in the silane solution for 1 minute each then cured at 80 °C in a furnace. To create the zeolite solution in this embodiment, 90wt% of AQSOA Z02 was added to the remaining silane solution. After manually breaking down large clumps of zeolite the solution was left to sonicate for 15 min followed by 15 minutes of magnetic stirring ensuring a homogenous suspension. Each sheet was left in the sorbent coating slurry for 1 minute and then suspended in the furnace at 80 °C for 2 hours for the final cure. Inside the furnace the sheets were elevated so as not disturb the coat on the bottom side of the fins. The coatings were measured using a micrometer to average the thickness across 9 points of the fin. The average thickness of the coating was a per side coating thickness of 0.373 mm which corresponds to an average mass distribution of 0.168 (k9s°^ent).

[0033] In some embodiments, the at least one fin 112 comprises an adsorbent material. In some embodiments, the at least one fin 112 comprises a metal-organic framework (MOF). Insome embodiments, the metal foam 114 has a plurality of open cell pores impregnated with an adsorbent material. In some embodiments, the absorbent material comprises an MOF material. In some embodiments, the adsorbent material comprises aluminum fumarate powder, zeolite, silica gel, hydrogel, or combinations thereof. In some embodiments, aluminum fumarate powder is used as the MOF material, as it has shown a large uptake step occurring between 20-30% relative humidity. In some embodiments, the foam portions 114 are infiltrated with aluminum fumarate. In some embodiments, an adsorbent powder is impregnated into the open cell pores of the foam pieces 114 using a submersion infiltration process, where the adsorbent powder is aluminum fumarate. In some embodiments, the adsorbent used is a zeolite material, such as AQSOA Z02. AQSOA Z02 is a man-made zeolite with lower uptake but faster kinetics at lower relative humidity than aluminum fumarate.

[0034] In one embodiment, about 34.9±6 g of sorbent on average was infiltrated into the foam pieces of the fins. In a 14-fin AHX, this results in about 488 g of adsorbent material in the adsorber structure, such as aluminum fumarate.

[0035] As shown in FIG 1 C in additional detail, the AHX further comprises a housing 119 for enclosing the plurality of fins 112, in some embodiments. In some embodiments, the housing further comprises an outlet 120 for releasing water vapor from the heat exchanger and an inlet 121 for receiving ambient air into the heat exchanger. In the embodiment shown, the water collection tank 108 is coupled to the AHX 101 via a coupling that is easily disconnected and reconnected to enable an operation mode as described below. In this embodiment, when the AHX 101 is connected to the water collection tank 108, a closed loop is formed. In the embodiment shown, the housing 119 was 3D printed using polylactic acid. The housing panel 122 through which the heat pipes 102 enter the AHX was fabricated using aluminum. In FIG. 1C, the heat pipes are shown covered by a heatshield. In some embodiments, the AHX 103 comprises an intake manifold 125 to distribute the air flow across the fins. In some embodiments, the manifold 125 is 3D printed and attached using RTV sealant.

[0036] In some embodiments, the at least one heat pipe comprises a working fluid to transfer thermal energy from an evaporator section of the heat pipe to a condenser section. In some embodiments, the at least one heat pipe comprises a copper-water sintered wick heat pipe.In the embodiment shown, the condenser section of the heat pipes is embedded in the heat block 104, which comprises copper. The condenser section of the heat pipes runs through the fins 112, and the pipes were bent at a 90-degree angle to ensure that the heat source is sufficiently separated from the AHX.

[0037] In some embodiments, at least one of the plurality of heat pipes is configured to be heated by a heat source external to the housing. In some embodiments, the heat source 105 is fuel-driven and comprises a fuel tank 116 and at least one fuel burner 117 proximate to the heat block 104, as shown in FIG. 1 A. In some embodiments, the application of burner heat to the bottom surface of the heat block 104 presents a safe method for transferring heat from a burner to the AHX in the system without damaging or contaminating the sorbent. In some embodiments, the fuel is kerosene. In some embodiments, the heat source is electrically driven and comprises heaters in the heat block 104. For example, in some embodiments, the heat block 104 comprises two embedded cartridge heaters to deliver electrical heating, each having a maximum load of 150W for a total combined 300W of power possible. Electrical heating can be advantageous for indoor use. For example, electrical heating can be controlled via a voltage supply to deliver a constant 275W of power to the heating block for desorption. In some embodiments, both electrical heating and a burner-based heat source is included in the system. In some embodiments, the heat source is driven via a coolant that flows through the heat pipes. The coolant is heated, in some embodiments, by waste heat sources such as automobile exhaust, industrial waste heat, etc., by solar thermal collectors, or combinations thereof. Thus, in some embodiments, a centralized copper block serves as a uniform evaporator for all, in some embodiments eight, heat pipes of the assembly and can accept heat in the form of embedded heaters or direct proximity to fuel driven fire as a means to desorb the AHX.

[0038] In some embodiments, therefore, an array of heat pipes is utilized as a passive method to transfer heat to the AHX from a copper heating block. Heat pipes provide very high thermal conductivity for a passive system without use of complex fluid loops to deliver regenerative energy. When using heat pipes it is important to consider common failure mechanisms related to temperature and heat load: sonic limit, entrainment limit, viscous limit, and capillary limit. In some embodiments, the heat pipes are designed to operate below these failure mechanisms. To facilitate that the as much of the adsorber heat exchanger as possiblereaches the target desorption temperature of 125°C, the heat pipes are substantially uniformly distributed across the stack. In some embodiments, an FEA model was developed to test a range of heat pipe configurations to determine the desired number and arrangement for the heat pipes. With the desired configuration and number of heat pipes selected for the system the dimensions and construction of the heating assembly were fixed. Fabrication of the heat pipe assembly involved forming, bending, and furnace soldering heat pipes to the main copper heating block. The MOF fins were adhered to the heat pipes using thermal epoxy which serves to limit the thermal contact resistance and provide mechanical stability for the AHX.

[0039] In some embodiments, the heater block is actively cooled by an external cooling mechanism such as a vapor compression cycle or thermoelectric modules during adsorption of water into the AHX. This helps reduce the temperature of the adsorbent contained in the AHX and actively dissipate the generated heat due to adsorption (exothermic reaction). Such cooling methods can increase uptake and consequently water yield per cycle.

[0040] The finned heat exchanger form factor of the AHX takes advantage of advection in both heat and mass transfer in some embodiments. Some embodiments of the system 100 further comprise a blower 111 configured to provide ambient air into the system and to increase the flow of air and water vapor within the system. As shown in FIG. 1 A, the blower I l l is disposed, in this embodiment, on the first conduit 107. In some embodiments, the blower 111 is a suction or vacuum blower. In one embodiment, a variable-speed DC blower with a maximum stagnation pressure of 7.5 kPa and a maximum volumetric flow rate of 73 cfm was selected. In some embodiments, a potentiometer was used to manually adjust the blower air speed which was measured using a vane anemometer located in the flow after the condenser.

[0041] With reference to FIGs. 2A and 2B, the general operation of some embodiments of the present technology will be described. The system 100 operates in two phases: (1) adsorption and (2) desorption. During the adsorption phase, the AHX 101 is disconnected from the condenser and the water tank, as shown in FIG. 2A. In some embodiments, this is achieved as shown whereby the coupling between the water tank and AHX is disconnected. In other embodiments, the coupling between the AHX and the condenser is also disconnected. The blower 111 is switched on to pull ambient air 123 into the inlet 121 and through the AHX 101.During this process, water vapor diffuses into the adsorber structure 103. Once the structure is saturated, the desorption phase is begun, as shown in FIG. 2B. The AHX is connected to the condenser and water tank, forming a closed loop. Heat is then applied to the heat block 104 by the heat source 105. This heat is transmitted to the adsorber structure 103 via the heat pipes 102. This heating process is illustrated schematically by arrow 118 in FIG. 2B. The adsorbent fins 112 are thereby heated by the heat source for passive thermal energy transport. This desorbs the water from the adsorber structure. The vapor-rich air stream 124 emanating from the AHX is cooled to ambient temperature by the condenser (a heat exchanger in this embodiment), facilitating water condensation. The condensed water is collected in the water collection tank. In this embodiment, after leaving the tank, the dehumidified air stream returns to the AHX to collect more desorbed water, preventing water vapor loss from the system. The condensed, liquid water is collected in the water collection tank 108.

[0042] In some embodiments, during desorption the system is sealed from the ambient and the role of the blower shifts to internal vapor transportation. Water vapor being released in the AHX travels to the condenser; in a passive system transportation of the desorbed vapor is purely diffusive. Relying on diffusion will create a mass transfer resistance barrier that scales with the distance between the condenser and the AHX. In some embodiments, in addition to decreasing mass transfer resistances the use of forced air through the condenser improves the heat transfer from the hot air stream to the environment while passing through the condenser. By closing the system during desorption, water vapor leaving the condenser in the gaseous state was routed such that the system recycled the same air during desorption. Trapping the non-condensed water vapor will prevent water from leaving the system, raising the absolute humidity of the air in the entire system.

[0043] In some embodiments, the condenser 106 is a heat exchanger. In some embodiments, the condenser 106 is a compact cross-flow heat exchanger with a single pass vertical internal geometry that reduces or prevents entrapment of condensate during desorption. In one embodiment, the condenser includes 18 single-pass vertical channels, emanating and ending in a horizontal header. In some embodiments, each vertical channel is a flat channel measuring 6 mm by 26 mm, leading to an estimated hydraulic diameter (D / ;) of 3.7 mm. In some embodiments, two DC fans (14 V, 0.5 A) are used to force ambient air across the condenser finsto improve the rejection of condensation latent heat. Thus, in some embodiments, the heat exchanger rejects heat to the ambient environment for condensation. In some embodiments, the condenser 106 includes a hollow tank that houses extended surfaces, such as fins or plates. These surfaces are integrated with multiple heat pipes in some embodiments. The function of these heat pipes is twofold: maintaining a uniform temperature distribution and aiding in efficient heat rejection during the condensation process. The heat pipes utilize the principle of evaporation to remove heat from the condensing vapor. The use of heat pipes enables a significant increase in the surface area available inside the hollow tank. In some embodiments, the design also allows flexibility in heat rejection direction by varying the grounding configurations of these heat pipes. Some embodiments include making direct contact with the condenser walls or interfacing with external heat exchangers. In some embodiments, the condensing surfaces incorporate millimetersized elements promoting droplet-based condensation instead of film-based condensation. Some embodiments utilize surfaces treated with hydrophobic or superhydrophobic coatings for improved condensation efficiency.

[0044] FIGs. 3A and 3B show an alternative embodiment of an atmospheric water harvesting system 300. The embodiment in FIGs. 3A and 3B comprises an integrated system for easier portability and stowage, in which the various components are housed within a single enclosure 319. In this embodiment, the adsorber structure 303 comprises a plurality of vertically stacked fins 312, with heat pipes 302 extending therethrough vertically from the horizontal heat block 304. The burner 317 is fed by fuel tank 316 to supply heat to the heat block 304. The condenser 306 comprises one or more fans 326, which are positioned to move air across the condenser elements to improve condensation. The system 300 includes an integrated water collection tank 308, which, in this embodiment, includes a drawer 327 for accessing the liquid water produced by the system. The system 300 also includes an inlet 321 through which ambient air can be drawn by the fans 311.

[0045] FIGs. 3C and 3D schematically show the operation of the system 300. FIG. 3C shows the adsorption process. Inlet 321 is opened and the air-flow fans 311 are initiated to pull ambient air 323 in through the inlet to saturate the adsorber structure 303. The air circulates through the system 300 and out an outlet 328. FIG. 3D shows the desorption process. Once the desired level of saturation in the adsorber structure 303 is achieved, the inlet 321 is closed, andthe heat source, burner 317, is turned on. This heats the heat block 304, which in turn heats the heat pipes 302 and the fins 312 of the adsorber structure 303. The fans 311 will then be pushing warm, vapor-rich air 324 into the condenser 306. Fans 326 help force the vapor-rich air across the condenser elements. Liquid water will then condense in the condenser and flow into the water collection tank 308.

[0046] In some embodiments, one or more additional adsorbing modules located downstream of the condenser are utilized so that the adsorption phase can be bolstered by the high humidity stream caused by condensation. The adsorption phase of the downstream module will have improved adsorption kinetics and uptake potential given the high humidity. In addition, the uncondensed water vapor that would normally be lost to the environment is captured in the second module for extraction later.

[0047] FIG. 4A shows a perspective view of the inner components of another alternative embodiment of an atmospheric water harvesting system 400. In this embodiment, the system 400 includes two AHX modules 401 and 430 that operate in phase with synchronized adsorption and desorption cycles. In this embodiment, the AHX modules 401 and 430 have the same design and are interchangeable in the system 400. Each AHX module is coupled to a condenser 406 and airflow conduits between the system components. The housing 431 includes a tank space 432 for the water collection tank that is coupled to the condenser 406.

[0048] FIG. 4B shows a perspective exploded view of some components of the AHX modules 401 and 430. Each module comprises a heat source 405, which is configured to provide heat to a heat block 404. In the embodiment of FIG. 4, the heat source 405 is an electric cartridge heater, for example an Ultramic heater from Watlow. The heat block 404 is coupled to a plurality of heat pipes 402 in this embodiment, which are also coupled to the adsorber structure 403. In this embodiment, the adsorber structure 403 is similar to a CPU cooler, but with adsorber coating (as described above) applied to the fins. Thus, in the system 400, because two AHX modules are included, the system comprises a second heat source; a second heat block configured to be heated by the second heat source; at least one second heat pipe coupled to the second heat block; and a second AHX coupled to the at least one second heat pipe. The secondAHX comprises a second adsorber structure and is configured to receive heat from the second heat block to heat air within the second AHX and release water vapor.

[0049] The AHX modules further comprise an adsorber housing 433 coupled to a base 434. In some embodiments the housing 433 is acrylic and includes two circular cutouts 435 to enable air flow across the adsorber structure 403.

[0050] FIG. 4C shows a perspective view of a complete AHX module. A fan 411 is included in a lower portion of the module and is coupled to one of the cutouts 435. The fan 411 is configured to drive air through the system 400 as explained below. Each AHX module is configured to couple to the system 400 via a vertical rail system integrated into the module housing 436.

[0051] FIG. 4D shows a front view of a complete system 400, with two AHX modules 401, 430 in place. The system includes an electrical box 437, which houses components for receiving electrical power from, for example, a wall outlet, and for providing electrical power to the fan and heater of the AHX module positioned above it. In some embodiments, the box 435 also includes components for powering one or more thermocouples for monitoring temperatures at various parts of the AHX. The electrical box also includes, in this embodiment, intake holes 438, which are configured for the intake of ambient air into the system for water harvesting.

[0052] The system 400 is configured to permit continuous water harvesting with the two AHX modules operating in unison, with one in a desorption phase while the other is in an adsorption phase. The desorbing module (in FIG. 4D, AHX module 430) is connected to the electrical box and, once desorption is desired, the heat source 405 and fan 411 is activated so that ambient air 439 is drawn into the system. The adsorber structure 403 desorbs the water it previously adsorbed, and this stream of water vapor 440 moves into the condenser 406, where some of the water condenses and liquid water 409 flows to the collection tank.

[0053] In this dual AHX system, the second AHX module 430 is downstream of the condenser 406. It receives the high humidity air flow 441 exiting the condenser and utilizes this flow to adsorb water. Thus, the downstream AHX 430 in this embodiment is the adsorbingmodule, such that it undergoes adsorption during desorption of the first AHX 401. Dried air 442 exits the system after passing through the adsorber structure of the AHX 430.

[0054] In this embodiment, once the desorption of module 401 is complete, the modules are swapped in the system so that module 430 can undergo desorption while 401 adsorbs again. The modules are repeatedly swapped to achieve continuous water harvesting.

[0055] Thus, aspects of the present disclosure, in some embodiments, are directed to the design, fabrication, and testing of compact, fuel-based water harvesting systems and components able to cycle several times per day without solar-thermal conversion and with minimal use of electrical energy. In some embodiments, aluminum fumarate, a MOF, was selected to be the adsorbent material due to the large uptake step occurring between 20-30% relative humidity. The adsorption conditions were >30% relative humidity in some embodiments allowing for cycle operation near the isotherm step. Heat pipes passively deliver heat from the fuel fired regeneration heat source outside of the AHX to the aluminum fumarate in the fins during desorption. Released water vapor is actively removed from the AHX during desorption and transported to the condenser, a compact heat exchanger that rejects heat to the ambient for condensation. Condensed water is collected at the exit of the condenser. In some embodiments, the system achieved 523.5 gwaterkMoFday^ of liquid condensate across 5 outdoor cycles. Neglecting the condenser limitations of the system the theoretical potential can be measured via the adsorbed water, one embodiment of the system achieved 849.8 water MOpday-1adsorbed during outdoor testing. The use of heat pipes as a passive heat transfer mechanism allows for a compact adsorbent heat exchanger form factor adsorbing 45.1 kgwater(m3)^HXday~'iin some embodiments. Some embodiments of the present technology improve the practicality and portability of water harvesters. Indoor experiments were subjected to a more controlled environment which led to improved performance of 1992.0 gwaterkgMOpday-1and 105.7water adsorption during testing.

[0056] In some embodiments, the metal substrates of the AHX are coated using silane binders with other sorbent powders. In some embodiments, this is done using a dip coating method for rapid cycling and stable construction. Coating heat exchangers allows for dense packaging of sorbent materials that maintain rapid sorption kinetics due to their thin nature.

[0057] In some embodiments, a DC vacuum pump is connected to the condenser. Upon activation, a vacuum environment is created within the absorber and condenser, leading to enhanced desorption and improved condensation yield in the absence of non-condensable gases. In some embodiments, a selective membrane to only pass water molecules through the condenser is used in conjunction with the vacuum pump. Pure steam will condense much more efficiently to improve overall water harvesting production.

[0058] In some embodiments, a vacuum is applied to the AHX during the desorption phase to improve desorption efficiency. Adsorption equilibrium is a function of pressure meaning that a slight vacuum will reduce the regeneration temperature required for desorption. This can reduce the overall energy requirement and lower the operating temperature of the system.

[0059] In some embodiments, the AWH system includes multiple absorbers in rotating or translating assemblies, ensuring continuous desorption and consistent water production. With a rotating or translating assembly, the system ensures a continuous supply of water. This is achieved as multiple absorbers simultaneously undergo the adsorption process, with at least one adsorber being in the desorption phase, resulting in water production.

[0060] In some embodiments, the AWH system includes distributed absorbers. In some embodiments, the primary modules, such as the heater and condenser, are centralized (e.g., on a military vehicle). In such embodiments, the energy to operate the AWH system is provided by diverse sources, such as waste heat of combustion, stored battery energy, etc. In such embodiments, instead of each user (e.g., each soldier on the military vehicle) carrying the AWH system, each user is equipped with a modularized and parallelized absorber unit. These units include, in some embodiments, integrated fans, sensors for humidity and temperature, and compact lithium-ion batteries. As users carry out their operations, their individual absorber units capture atmospheric water vapor. When water production is desired, they connect their absorber module to the central unit, initiating the desorption and subsequent water production processes.

[0061] As will be apparent to those skilled in the art, various modifications, adaptations, and variations of the foregoing specific disclosure can be made without departing from the scope of the technology claimed herein. The various features and elements of the technology described herein may be combined in a manner different than the specific examples described or claimedherein without departing from the scope of the technology. In other words, any element or feature may be combined with any other element or feature in different embodiments, unless there is an obvious or inherent incompatibility between the two, or it is specifically excluded.

[0062] References in the specification to “one embodiment,” “an embodiment,” etc., indicate that the embodiment described may include a particular aspect, feature, structure, or characteristic, but not every embodiment necessarily includes that aspect, feature, structure, or characteristic. Moreover, such phrases may, but do not necessarily, refer to the same embodiment referred to in other portions of the specification. Further, when a particular aspect, feature, structure, or characteristic is described in connection with an embodiment, it is within the knowledge of one skilled in the art to affect or connect such aspect, feature, structure, or characteristic with other embodiments, whether or not explicitly described.

[0063] The term "and / or" means any one of the items, any combination of the items, or all of the items with which this term is associated.

[0064] Each numerical or measured value in this specification is modified by the term “about.” The term "about" refers to a variation of ± 10% of the value specified unless stated otherwise. Unless indicated otherwise herein, the term "about" is intended to include values and ranges proximate to the recited range that are equivalent in terms of the functionality of the composition, or the embodiment.

[0065] As will be understood by one skilled in the art, for any and all purposes, particularly in terms of providing a written description, all ranges recited herein also encompass any and all possible sub-ranges and combinations of sub-ranges thereof, as well as the individual values making up the range, particularly integer values. A recited range (e.g., weight percents of carbon groups) includes each specific value, integer, decimal, or identity within the range. Any listed range can be easily recognized as sufficiently describing and enabling the same range being broken down into at least equal halves, thirds, quarters, fifths, or tenths. As a non-limiting example, each range discussed herein can be readily broken down into a lower third, middle third, and upper third, etc.

Claims

Claims1. An atmospheric water harvesting system comprising: a heat source; a heat block configured to be heated by the heat source; at least one heat pipe coupled to the heat block; and an adsorbent heat exchanger (AHX) coupled to the at least one heat pipe, the AHX comprising an adsorber structure and configured to receive heat from the heat block to heat air within the AHX and release water vapor.

2. The system of claim 1, wherein the adsorber structure comprises at least one fin coupled to the at least one heat pipe.

3. The system of claim 2, wherein the at least one fin comprises an adsorber coating.

4. The system of claim 2, further comprising that the at least one fin comprises a plurality of fins wherein each fin separated from adjacent fins by a gap.

5. The system of claim 4, wherein each of the plurality of fins comprises a metal sheet and the adsorber coating comprises a zeolite material.

6. The system of claim 5, wherein the metal sheet comprises aluminum and the adsorber coating comprises AQSOA Z02.

7. The system of claim 4, wherein each of the plurality of fins comprises metal foam coupled to a metal sheet, the metal foam having a plurality of open cell pores impregnated with an adsorbent material.

8. The system of claim 7, wherein the metal foam and the metal sheet comprise copper, aluminum, or combinations thereof.

9. The system of claim 8, wherein the adsorbent material comprises a metal-organic framework (MOF).

10. The system of claim 9, wherein the adsorbent material comprises aluminum fumarate powder.

11. The system of claim 1, wherein the heat source is fuel-driven and comprises a fuel tank and at least one fuel burner proximate to the heat block.

12. The system of claim 1, wherein the heat source is electrically driven and comprises heaters in the heat block.

13. The system of claim 1, further comprising: a condenser coupled to the AHX, the condenser configured to receive the water vapor released from the AHX and to release liquid water; and a water collection tank coupled to the condenser, the water collection tank configured to collect the liquid water released from the condenser.

14. The system of claim 13, further comprising a blower configured to provide ambient air into the system and to increase the flow of air and water vapor within the system.

15. The system of claim 13, further comprising: a second heat source; a second heat block configured to be heated by the second heat source; at least one second heat pipe coupled to the second heat block; and a second adsorbent heat exchanger (AHX) coupled to the at least one second heat pipe, the second AHX comprising a second adsorber structure and configured to receive heat from the second heat block to heat air within the second AHX and release water vapor; wherein the second AHX is coupled to the condenser and the system is configured such that the second AHX is downstream of the AHX and the condenser and undergoes adsorption during desorption of the AHX.

16. A heat exchanger, comprising: at least one heat pipe; an adsorber structure comprising at least one fin coupled to the at least one heat pipe, the at least one fin comprising an adsorbent material.

17. The heat exchanger of claim 16, further comprising that the at least one heat pipe comprises a plurality of heat pipes and the at least one fin comprises a plurality of fins arranged parallel to each other, and wherein each fin is separated from adjacent fins by a gap; and wherein each of the plurality of fins is coupled to at least one of the plurality of heat pipes.

18. The heat exchanger of claim 17, wherein each of the plurality of fins comprises a metal sheet coated with a zeolite material.

19. The heat exchanger of claim 18, further comprising a housing for enclosing the plurality of fins; wherein at least one of the plurality of heat pipes is configured to be heated by a heat source external to the housing.

20. The heat exchanger of claim 19, wherein the housing further comprises an outlet for releasing water vapor from the heat exchanger and an inlet for receiving ambient air into the heat exchanger.

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