Moisture-absorbing phase-change capsule for regulating heat and humidity and extracting water from air and preparation method of moisture-absorbing phase-change capsule

Abstract

The preparation method comprises the following steps: step 1, mixing sodium alginate, silica gel powder, polyvinylpyrrolidone and expanded graphite according to a mass ratio, dissolving the mixture in deionized water to form slurry, dropwise adding the slurry into a CaCl2 solution by an injection and drop method for cross-linking, and standing to prepare composite drying agent microspheres; and 2, pre-freezing the composite drying agent microspheres, carrying out vacuum freeze drying, impregnating the composite drying agent microspheres in a molten phase change material, and drying the impregnated composite material in a drying oven to finally prepare the moisture absorption phase change capsule. According to the moisture-absorption phase-change capsule prepared by the preparation method disclosed by the invention, the phase-change material and the moisture-absorption material are compounded, reinforced materials such as expanded graphite and PVP (Polyvinyl Pyrrolidone) are integrated, finally, the capsule is packaged to be convenient to use and recycle, and the prepared moisture-absorption phase-change capsule has the functions of efficiently absorbing moisture, cooperatively regulating and controlling temperature and humidity and driving water by solar energy; the device has the advantages of being high in structural stability, high in packaging leakproofness, low in operation energy consumption and the like.

Description

Technical Field

[0001] The present invention relates to the technical field of moisture-absorbing phase change composite materials, and particularly relates to a moisture-absorbing phase change capsule for thermal and humidity regulation and air water harvesting and a preparation method thereof. Background Art

[0002] At present, air water harvesting technologies mainly include condensation method and adsorption-desorption method; traditional moisture-absorbing materials have performance attenuation due to temperature increase; single phase change materials lack moisture-absorbing function and are difficult to synergistically regulate temperature and humidity; the condensation method requires continuous power supply and cannot adapt to off-grid scenarios; simple physical blending structures are prone to failure and have insufficient cycling performance.

[0003] The patent with the publication number of CN119686417A proposes an air water harvesting device based on the condensation principle, but it relies on electric drive, has high energy consumption and is difficult to be applied in a power-free environment. Although traditional moisture-absorbing materials (such as silica gel, calcium chloride) have good moisture-absorbing performance, there are defects: insufficient thermal stability: the heat released during the moisture-absorbing process causes the material temperature to rise, and the moisture-absorbing efficiency drops significantly; single function: traditional phase change materials are only used for temperature regulation and cannot achieve synergistic regulation of temperature and humidity; unstable structure: and most existing moisture-absorbing materials are in powder or granular form, the materials are easy to leak and difficult to encapsulate. Summary of the Invention

[0004] In order to overcome the above technical problems, the purpose of the present invention is to provide a moisture-absorbing phase change capsule for thermal and humidity regulation and air water harvesting and a preparation method thereof. The moisture-absorbing phase change capsule prepared by the preparation method of the present invention composites a phase change material and a moisture-absorbing material, integrates reinforcing materials such as expanded graphite, PVP, etc., and finally is convenient for use and recycling through capsule encapsulation. The prepared moisture-absorbing phase change capsule has the functions of high-efficiency moisture absorption, synergistic regulation of temperature and humidity, and solar-driven water harvesting, and has the advantages of strong structural stability, high encapsulation tightness, low operation energy consumption, etc.

[0005] In order to achieve the above purpose, the technical solution adopted by the present invention is:

[0006] A moisture-absorbing phase change capsule for thermal and humidity regulation and air water harvesting, comprising a three-dimensional gel framework constructed by cross-linking sodium alginate and calcium ions to form a high-strength porous encapsulation shell, and the phase change material is stably embedded in the pores of the three-dimensional gel framework through capillary force.

[0007] The moisture-absorbing phase change capsule has a loose porous structure, with a specific surface area ≥ 300m 2 / g, and the porosity of the loose porous structure is 65% - 75%;

[0008] The surface of the moisture-absorbing phase change capsule shows irregular roughness and micro-cracks, which are used to increase the specific surface area of the material and provide more adsorption sites.

[0009] This rough surface property is beneficial to the adsorption capacity of the moisture-absorbing material in a humid environment because it increases the contact area with moisture and also provides more diffusion channels for the molecules that adsorb moisture.

[0010] Cracks and pores contribute to the rapid diffusion of water molecules inside the material, shortening the diffusion path of water molecules and further accelerating the moisture absorption rate. The combination of the distribution of the phase change material and these micropores not only improves the thermal stability of the material but also promotes the efficient storage and release of heat during the phase change process.

[0011] A preparation method of a moisture-absorbing and phase-changing capsule for thermal and humidity regulation and air water harvesting includes the following steps;

[0012] Step 1: Mix sodium alginate, silica gel powder, polyvinylpyrrolidone, and expanded graphite according to a mass ratio, dissolve them in deionized water to form a slurry, and drop the slurry into a CaCl2 solution by the dropping method for crosslinking, then let it stand to obtain composite desiccant microspheres;

[0013] Step 2: Pre-freeze the composite desiccant microspheres, vacuum freeze-dry them, and then immerse them in molten phase change material. After impregnation, the composite material is dried in an oven to finally obtain the moisture-absorbing and phase-changing capsule.

[0014] In the said Step 1, sodium alginate, silica gel powder, polyvinylpyrrolidone, and expanded graphite are mixed according to a mass ratio of 5:1:0.5:12; and are dropped into a 15wt% CaCl2 solution by the dropping method for crosslinking.

[0015] In the said Step 1, the dropping rate of the dropping method is 40 mL / min, so that the shape of the unformed composite desiccant microspheres is a round water droplet shape, and the diameter of the cross-section of the capsule is controlled at 3 - 5 mm. The crosslinking and curing time is 12 h, and the calcium ions in the solution induce a crosslinking reaction to make the composite desiccant microspheres fully formed.

[0016] In the said Step 2, pre-freeze to -30 °C, vacuum freeze-dry for 18 h, control the impregnation time to 2 h, and the mass ratio of the composite desiccant microspheres to the phase change material is 3:2;

[0017] The composite material is dried in an oven at 50 - 55 °C for 18 - 30 h.

[0018] In the said Step 2, the temperature limiting condition of the molten phase change material is: 40 - 50 °C.

[0019] In the said Step 2, the phase change material is specifically MA-SA-CA (myristic acid - capric acid - stearic acid).

[0020] In the said Step 2, the vacuum degree of the freeze-drying ≤ 10 Pa.

[0021] The described moisture-absorbing phase change capsules are applied to the coordinated regulation of indoor temperature and humidity in buildings, as well as distributed water extraction in agricultural irrigation and emergency disaster relief.

[0022] The described moisture-absorbing phase change capsules are applied to water-scarce areas, where liquid water is obtained by adsorbing water vapor in the air at night and desorbing it driven by solar energy during the day in water-scarce areas.

[0023] The above applications are realized through an air water intake device based on adsorption. The device has a transparent and airtight structure. The upper layer is provided with a moisture-absorbing phase change capsule layer laid on a filter plate, and the lower layer is a water storage container. At night, the top cover of the device remains open, and the moisture-absorbing phase change capsules in the moisture-absorbing phase change capsule layer naturally adsorb water vapor in the air. During the day, the top cover of the device is closed. At this time, the inside of the device is in an airtight condition, and solar energy penetrates the side wall of the device to heat the moisture-absorbing phase change capsules. At this time, the humidity inside the device is extremely low, and the moisture-absorbing phase change capsules lose their moisture-absorbing ability under extremely low humidity conditions, triggering the rupture of hydrogen bonds and van der Waals forces in the adsorbent, causing the adsorbed water to desorb into water vapor and condense into liquid water through a gas-liquid separation structure in the airtight device.

[0024] In the moisture-absorbing phase change capsule layer, the moisture-absorbing phase change capsules are evenly spread over the filter plate without stacking, ensuring full contact of the material with sunlight.

[0025] Advantages of the present invention:

[0026] Coordinated regulation of temperature and humidity: During the moisture-absorbing process, traditional materials release heat of absorption due to adsorbing water, resulting in local temperature rise of the materials, significantly reducing the subsequent moisture-absorbing ability. However, the invented moisture-absorbing phase change capsules embed a ternary fatty acid phase change material (MA-SA-CA) in the structure, and its melting temperature (about 23.76 °C) highly matches the temperature of heat of absorption release. When the heat of absorption is released, the phase change material simultaneously undergoes a solid-liquid transformation, absorbs heat and maintains the system temperature within a stable range (fluctuation ≤ 1 °C). This thermal buffering mechanism effectively avoids the problem of local overheating inhibiting moisture absorption, significantly enhances the moisture-absorbing driving force, and makes the overall moisture-absorbing performance increase by more than 30% compared with a single moisture-absorbing material.

[0027] Under high temperature and low humidity conditions during the day, the moisture-absorbing phase change capsules absorb solar radiation and heat up through a transparent and airtight device. The internal phase change material returns from a liquid state to a solid state, releases latent heat and synergistically improves the overall thermal energy utilization rate. This process triggers the rupture of hydrogen bonds and van der Waals forces in the adsorbent, causing the adsorbed water to desorb into water vapor and condense into liquid water through a gas-liquid separation structure in the airtight device. Experimental verification shows that under the condition of no external electrical energy input, the material can desorb 93% of the adsorbed water within 6 hours in an environment with an average solar radiation intensity of 900 W / m 2 / h and an average temperature of about 35 °C. Even in cloudy days (45 W / m 2 / h), it can reach 60%, showing extremely strong passive water release ability and environmental adaptability.

[0028] A three-dimensional gel skeleton is constructed through sodium alginate-calcium ion cross-linking to form a high-strength porous encapsulation shell, which can achieve a high loading of phase change materials (mass fraction 40%). The phase change materials are stably embedded in the pores through capillary force, and the leakage rate is less than 2%, effectively preventing liquid seepage during the heating and desorption process. In addition, the porous network structure not only enhances the moisture absorption channels but also improves the overall mechanical stability and deformation recovery ability. The results of the air water intake experiment show that the water production performance remains above 95% after 50 consecutive adsorption and desorption cycles.

[0029] Widely applicable: suitable for water intake in water-scarce areas, agricultural irrigation, and humidity regulation for building energy conservation. Brief Description of the Drawings

[0030] Figure 1 It is a flow chart for capsule preparation (drop-casting method, cross-linking, freeze-drying, and impregnation processes).

[0031] Figure 2 It is a structural diagram and schematic diagram of the dehumidification system device.

[0032] Figure 3 It is a test curve of the moisture absorption performance of the system (moisture absorption amount at different temperatures and humidities).

[0033] Figure 4 It is a structural diagram of the air water intake device (including a moisture absorption layer, a condensation layer, and a water storage tank).

[0034] Figure 5 It is a test curve of the air water intake performance (moisture desorption rate at different temperatures and solar radiation irradiances).

[0035] Figure 6 It is the test results of adsorption kinetics, DSC, TGA, and SEM (moisture absorption performance, phase change temperature, latent heat, thermal stability, and microstructure). Detailed Description of the Invention

[0036] The present invention will be further described in detail below with reference to the accompanying drawings.

[0037] As Figure 1 shown, the moisture absorption and phase change capsule for thermal and humidity regulation and air water intake, the moisture absorption and phase change capsule comprises the following components: matrix material: calcium alginate gel, providing a three-dimensional network structure;

[0038] moisture absorption material: a composite of silica gel powder and polyvinylpyrrolidone, enhancing the specific surface area and moisture absorption rate;

[0039] reinforcing agent: expanded graphite with a mass fraction of 15%, increasing the thermal conductivity (0.503 W / (m·K));

[0040] Phase change material: myristic acid-stearic acid-decanoic acid (MA-SA-CA) eutectic mixture (mass ratio 24.05:6.38:69.57), melting temperature 23.45°C, latent heat 147.89 kJ / kg, thermal decomposition temperature 101.3°C.

[0041] The capsule has a loose porous structure and a moisture absorption capacity of 0.58g / g (80% humidity). The water desorption rate from air can reach up to 93% (driven only by solar energy).

[0042] Compared with traditional hygroscopic materials, the hygroscopic process releases hygroscopic heat, or the temperature rises when used in a high temperature environment. As the temperature rises, the moisture inside the material absorbs heat and undergoes an evaporation process, and the moisture is gradually released from the material, causing the water content of the material to decrease, so that the temperature rise directly affects the hygroscopic capacity of the material. The introduction of phase change materials can absorb hygroscopic heat or environmental heat, so that the temperature of the material remains unchanged and the hygroscopic performance is stabilized.

[0043] Compared with simple physical blending, calcium alginate hydrogel is selected as the matrix to provide a stable three-dimensional network structure of hydrogel, assist in capsule formation, and quickly cool the carrier to a low temperature through freeze-drying technology, so that the water in the material changes from liquid to solid to form ice crystals. At low temperatures, the sublimation process of water is accelerated by reducing the pressure (vacuum). Due to the large volume of ice crystals, during the sublimation process, water evaporates from the material, and the ice crystals are removed, and pores are formed in the space originally filled with ice crystals. The void structure provides more accommodation space for subsequent impregnation of phase change materials. At the same time, the pore structure can adapt to the volume change of the material during the moisture absorption process, reduce mechanical stress, and extend the life of the material.

[0044] Compared to the condensation method (i.e. cooling the water vapor in the air and condensing it into water by lowering the temperature), the composite material of the present invention can naturally absorb moisture from the air (without the need for electric drive) due to the hygroscopic material therein, and can be desorbed using only low-grade thermal energy (such as solar energy, waste heat).

[0045] Embodiment 1:

[0046] Step 1: Slurry preparation and droplet crosslinking

[0047] 1. Raw material ratio: Weigh 1g silica gel powder (SG), 0.5g polyvinyl pyrrolidone (PVP) and 245g deionized water, pour into a beaker and stir with a magnetic stirrer for 20 minutes. Then add 5g sodium alginate (SA), and continue to stir with a mechanical stirrer for 1 hour to form a brown uniform slurry. Then add 12g expanded graphite (EG) and continue stirring for 2 hours until a stable suspension system is formed.

[0048] 2. Dropwise forming method: Load the slurry into a 30 mL syringe and vertically drop it into a 15 wt% CaCl2 solution at a dropping rate of 40 mL / min through a dual-channel micro-injection pump.

[0049] 3. Crosslinking and curing: The dropped slurry microspheres are left standing in the CaCl2 solution for 12 hours, and sodium alginate crosslinks with Ca 2 + to form stable calcium alginate gel microspheres.

[0050] Step 2: Freeze-drying and phase change material loading

[0051] 1. Freezing treatment: The crosslinked microspheres are first placed in a freeze-dryer and pre-frozen to below -30 °C to ensure that the internal moisture is completely solidified.

[0052] 2. Vacuum drying: Transfer to a vacuum drying oven (vacuum degree ≤ 10 Pa) and conduct freeze-drying for 18 hours to remove moisture and form a porous structure.

[0053] 3. Phase change material impregnation: The dried composite desiccant microspheres are blended with a ternary phase change material myristic acid - stearic acid - capric acid (MA - SA - CA) melted and mixed in a mass ratio of 24.05:6.38:69.57 in a beaker, and placed in an ultrasonic cleaner for impregnation for 2 h to allow it to fully penetrate into the porous structure.

[0054] 4. Drying and shaping: Dry in an oven at 50 °C for 18 hours to obtain the moisture-absorbing phase change capsules.

[0055] Example 2:

[0056] Step 1: Slurry preparation and dropwise crosslinking

[0057] 1. Raw material ratio: Weigh 1 g of silica gel powder (SG), 0.5 g of polyvinylpyrrolidone (PVP), and 245 g of deionized water, pour them into a beaker and stir with a magnetic stirrer for 30 min. Then add 5 g of sodium alginate (SA), and then continue to stir thoroughly with a mechanical stirrer for 1 h to form a brown homogeneous slurry. Then add 12 g of expanded graphite (EG) and continue to stir for 2 h until a stable suspension system is formed.

[0058] 2. Dropwise forming method: Load the slurry into a 30 mL syringe and vertically drop it into a 15 wt% CaCl2 solution at a dropping rate of 40 mL / min through a dual-channel micro-injection pump.

[0059] 3. Crosslinking and curing: The dropped slurry microspheres are left standing in the CaCl2 solution for 12 hours, and sodium alginate crosslinks with Ca 2 + to form stable calcium alginate gel microspheres.

[0060] Step 2: Freeze-drying and phase change material loading

[0061] 1. Freezing treatment: The crosslinked microspheres are first placed in a freeze dryer and pre-frozen to below -30 °C to ensure that the internal moisture is completely solidified.

[0062] 2. Vacuum drying: Transfer to a vacuum drying oven (vacuum degree ≤ 10 Pa), freeze-dry for 18 hours to remove moisture and form a porous structure.

[0063] 3. Phase change material impregnation: The dried composite desiccant microspheres are blended with a ternary phase change material myristic acid-stearic acid-capric acid (MA-SA-CA) melted and mixed in a mass ratio of 24.05:6.38:69.57 in a beaker, and placed in an ultrasonic cleaner for impregnation for 2 h to fully penetrate into the internal porous structure.

[0064] 4. Drying and shaping: Dry in an oven at 50 °C for 30 hours to obtain the moisture-absorbing phase change capsules.

[0065] Example 3:

[0066] Step 1: Slurry preparation and injection-drop crosslinking

[0067] 1. Raw material ratio: Weigh 1 g of silica gel powder (SG), 0.5 g of polyvinylpyrrolidone (PVP) and 245 g of deionized water, pour them into a beaker and stir with a magnetic stirrer for 25 min. Then add 5 g of sodium alginate (SA), and then continue to stir thoroughly with a mechanical stirrer for 1 h to form a brown homogeneous slurry. Then add 12 g of expanded graphite (EG) and continue to stir for 2 h until a stable suspension system is formed.

[0068] 2. Injection-drop molding: Load the slurry into a 30 mL syringe and vertically drop it into a 15 wt% CaCl2 solution at a dropping rate of 40 mL / min through a dual-channel micro-injection pump.

[0069] 3. Crosslinking and curing: The dropped slurry microspheres are left standing in the CaCl2 solution for 12 hours, and sodium alginate crosslinks with Ca 2 + to form stable calcium alginate gel microspheres.

[0070] Step 2: Freeze-drying and phase change material loading

[0071] 1. Freezing treatment: The crosslinked microspheres are first placed in a freeze dryer and pre-frozen to below -30 °C to ensure that the internal moisture is completely solidified.

[0072] 2. Vacuum drying: Transfer to a vacuum drying oven (vacuum degree ≤ 10 Pa), freeze-dry for 18 hours to remove moisture and form a porous structure.

[0073] 3. Phase change material impregnation: The dried composite desiccant microspheres were blended with the ternary phase change material myristic acid - stearic acid - capric acid (MA - SA - CA) which was pre - melted and mixed in a mass ratio of 24.05:6.38:69.57 in a beaker, and then placed in an ultrasonic cleaner for impregnation for 2 h to allow it to fully penetrate into the internal porous structure.

[0074] 4. Drying and shaping: Dry in an oven at 55 °C for 18 hours to obtain the moisture - absorbing phase - change capsules.

[0075] Example 4: As Figure 2 、 Figure 3 shown, the process and performance of the air dehumidification system were tested:

[0076] In the present invention, a fixed - bed dehumidification experimental device was used to verify the moisture - absorbing performance of the moisture - absorbing phase - change capsules for heat and moisture regulation and air water intake under flowing air. The gas source regulation unit configured at the front end of the system consists of three parts: an air compressor (as the gas source), an air heater (for adjusting the gas temperature), and an air humidifier (for adjusting the gas humidity).

[0077] The rear end of the system consists of four parts: an anemometer (range 0 - 20 m / s), a temperature and humidity sensor (temperature control range - 40 - 120 °C, humidity control range 0 - 100% RH), an Agilent data acquisition instrument (for collecting the changes in gas temperature and humidity), and an adsorption column (for observing the stacking of samples). Each subsystem works together to completely construct a dynamic dehumidification experimental platform that can accurately regulate gas parameters (flow rate 20 L / min), with real - time fluctuations in temperature and humidity, and real - time monitoring.

[0078] As Figure 2 b, air starts from the compressor, passes through the heater to adjust the temperature, and then enters the pipeline monitored by the anemometer and the temperature and humidity sensor. Then, the air is split through a T - joint and enters the moisture - absorbing column (the moisture - absorbing phase - change capsules are placed in the adsorption column) for humidity adsorption. Finally, all data is transmitted to the computer through the data acquisition device for processing and display.

[0079] The test results show that the moisture - dehumidification capacity of the moisture - absorbing phase - change capsules of the present invention is 0.465 g / (kg·s) ± 3.04% (inlet air 26 °C, relative humidity 75%);

[0080] Example 5: As Figure 4 、As Figure 5 shown, the application of the air water intake device:

[0081] To verify the air water intake function of the material, a simple air water intake device was built in this experiment. The physical diagram of the device and the schematic diagram of the air water intake process are shown in Figure 4The overall device is designed to be transparent and airtight. The top and sides are made of high-transparency materials to ensure sufficient sunlight irradiates the moisture-absorbing phase-change capsules. Inside the container, there is a dry-wet separation filter layer. The moisture-absorbing phase-change capsules are placed in the upper layer for adsorbing / desorbing moisture, and the lower layer is a water storage container for collecting the separated liquid water. When taking water, the moisture-absorbing phase-change capsules are evenly distributed above the filter layer to ensure sufficient contact with the air. During the air water intake process, the moisture-absorbing phase-change capsules mainly rely on four core steps: "adsorption - storage - desorption - condensation". By virtue of the thermo-hygroscopic response characteristics of the material itself, the cyclic extraction of moisture is achieved without electric drive.

[0082] The filter layer is made of a material that is light-proof as a whole to prevent the moisture desorbed and collected in the lower water storage box from being reheated and evaporated again. The small holes evenly distributed on the filter plate have a diameter of 2 mm, which can filter the moisture desorbed from the moisture-absorbing phase-change capsules into the water storage box.

[0083] Its basic reaction mechanism is as follows:

[0084] Moisture absorption stage (night / low temperature and high humidity conditions): When the relative humidity in the ambient air is relatively high (usually higher than 50% at night), the moisture-absorbing material (such as silica gel or calcium alginate hydrogel) in the moisture-absorbing phase-change capsules adsorbs water vapor molecules on the surface and inside of the porous structure through van der Waals forces and hydrogen bonds. The adsorption process is an exothermic reaction, which will cause the temperature of the material to rise, usually reducing the moisture absorption efficiency. However, the phase-change material (MA-SA-CA) embedded in the capsule will absorb the heat released during the moisture absorption process and undergo a solid → liquid phase change, effectively controlling the local temperature within a small fluctuation range (fluctuation ≤ 1°C) and stabilizing the moisture absorption capacity. Subsequently, the water vapor continues to diffuse into the interior in the pores of the material, forming layer-by-layer aggregated adsorption, and the material gradually reaches the moisture absorption saturation state.

[0085] Thermal-driven desorption stage (day / high temperature and low humidity conditions): Under sunlight conditions (boundary condition: total illuminance ≥ 270 W / m 2 )), the moisture-absorbing phase-change capsules are heated and the temperature rises. At this time, the phase-change material inside the capsule changes from liquid to solid, releasing the latent heat of phase change. The increase in temperature causes the intermolecular bond energy inside the adsorbent to be destroyed, and water molecules desorb and turn into water vapor. This process is an endothermic desorption reaction, and the material returns to its initial dry state and has the ability to absorb moisture again.

[0086] Water vapor migration and liquefaction: The desorbed water vapor accumulates in the upper layer of the capsule and gradually sinks to the lower space with a lower temperature in the transparent airtight water intake device. When the water vapor cools, it condenses on the inner wall of the device or the surface of the water storage layer, forming liquid water droplets and collecting in the collection tank. This process relies on natural condensation driven by temperature difference and can achieve liquid water recovery without energy consumption.

[0087] Recirculation Preparation: As the night temperature drops, the system gradually cools down. The phase change material returns to the solid state for heat absorption, and the desiccant regains its adsorption capacity, preparing to enter the next moisture absorption - desorption cycle.

[0088] Figure 3 The dehumidification effect of the fixed - bed dehumidification experimental device under different inlet air moisture contents is shown. This device simulates the actual use environment where it is affected by the flowing air disturbance, and the temperature and humidity of the environment are changing. However, the air moisture content curve still shows a downward trend, verifying the stability of the dehumidification performance of the moisture - absorbing phase - change capsules.

[0089] Appendix Figure 5 The moisture desorption curves of the air water - extraction device based on moisture - absorbing phase - change capsules under different temperatures and different solar radiation irradiances are shown. It can be seen from the figure that the higher the temperature and the stronger the average solar radiation irradiance, the higher the moisture desorption rate. Therefore, this moisture - absorbing phase - change capsule is especially suitable for the water - extraction needs in arid regions.

[0090] Figure 5 a is the curve of the moisture desorption rate of the air water - extraction device based on moisture - absorbing phase - change capsules varying with temperature. Figure 5 b is the curve of the moisture desorption rate of the air water - extraction device based on moisture - absorbing phase - change capsules varying with the average solar radiation irradiance during the test period.

[0091] As Figure 6 shown, the technical effect verification is carried out (in combination with Figure 6 ):

[0092] Figure 6 Figure a is the curve of the moisture absorption of the material varying with temperature, Figure b is the curve of the moisture absorption of the material varying with humidity, Figure c is the DSC test curve of the material, Figure d is the TGA test curve of the material, and Figure e is the microscopic structure diagram observed by SEM of the material.

[0093] Moisture Absorption Performance: The moisture absorption amount reaches 0.58 g / g at 26°C and 80% humidity, which is 40% higher than that of traditional silica gel.

[0094] Thermal Conductivity: 0.503 W / (m·K), and the thermal response speed is 3 times higher than that of traditional silica gel.

[0095] Air Water Extraction: When the average solar radiation intensity is 900 W / m 2 / h and the temperature is 35°C, the highest moisture desorption rate can reach 93%. The moisture - absorbing phase - change capsule (with a moisture absorption amount of 0.58 g / g at 80% humidity at night) can produce 0.54 L / kg of water per day on average the next day.

[0096] Circulation Stability: The performance decay is less than 5% after 100 cycles.

[0097] The present invention realizes co-regulation of temperature and humidity: the phase change material absorbs heat of absorption, the temperature fluctuation of the capsule is ≤1°C, and the moisture absorption efficiency is increased by 30%; the present invention has no electric drive: the solar desorption energy consumption is <1 kWh / L, which is suitable for off-grid areas; the present invention has structural stability: encapsulated in porous capsules, the performance attenuation is <5% after 100 cycles of use; the present invention has flexible applications: it can be integrated into building walls or independently deployed as a water intake device.

Claims

1. A hygroscopic phase change capsule for heat and humidity control and air water extraction, characterized in that: The method comprises cross-linking sodium alginate and calcium ions to construct a three-dimensional gel skeleton to form a high-strength porous encapsulation shell, and the phase change material is stably embedded in the pores of the three-dimensional gel skeleton through capillary force.

2. A hygroscopic phase change capsule for heat and humidity control and air water extraction according to claim 1, characterized in that: The hygroscopic phase-change capsule has a loose porous structure with a specific surface area of ​​≥300m 2 / g, the porosity of the loose porous structure is 65%-75%; The surface of the hygroscopic phase change capsules presents irregular roughness and tiny cracks, which are used to increase the specific surface area of ​​the material and provide adsorption sites.

3. A method for preparing a hygroscopic phase change capsule for heat and humidity control and air water extraction, characterized in that: The steps include: Step 1: Sodium alginate, silica gel powder, polyvinyl pyrrolidone and expanded graphite are mixed according to a mass ratio, dissolved in deionized water to form a slurry, and then dripped into a CaCl2 solution by a dropwise method for cross-linking, and allowed to stand to obtain composite desiccant microspheres; Step 2: pre-freeze the composite desiccant microspheres, vacuum freeze-dry them, and then immerse them in the molten phase change material. The impregnated composite material is dried in an oven to finally obtain the hygroscopic phase change capsules.

4. The method for preparing a hygroscopic phase change capsule for heat and humidity control and air water extraction according to claim 3, characterized in that: In the step 1, sodium alginate, silica gel powder, polyvinyl pyrrolidone and expanded graphite are mixed in a mass ratio of 5:1:0.5:12; and the mixture is dripped into a 15wt% CaCl2 solution for cross-linking by a dropwise method.

5. The method for preparing a hygroscopic phase change capsule for heat and humidity control and air water extraction according to claim 3, characterized in that: In the step 1, the dripping rate of the dripping method is 40 mL / min, so that the shape of the composite desiccant microspheres that have not yet been formed is a round water drop shape, and the cross-sectional diameter of the capsule is controlled to be 3-5 mm, and the cross-linking curing time is 12 hours.

6. The method for preparing a hygroscopic phase change capsule for heat and humidity control and air water extraction according to claim 3, characterized in that: In the step 2, the mixture is pre-frozen to -30°C, vacuum freeze-dried for 18 hours, the immersion time is controlled to be 2 hours, and the ratio of the composite desiccant microspheres to the phase change material is 3:2; The composite material is dried in an oven at 50-55°C for 18-30h.

7. The method for preparing a hygroscopic phase change capsule for heat and humidity control and air water extraction according to claim 3, characterized in that: In step 2, the temperature limit condition of the molten phase change material is: 40-50°C; In the step 2, the phase change material is specifically MA-SA-CA; The vacuum degree of freeze drying in step 2 is ≤10Pa.

8. The use of the hygroscopic phase change capsule for heat and humidity regulation and air water extraction according to any one of claims 1 to 7, characterized in that: The hygroscopic phase change capsules are used for coordinated control of indoor temperature and humidity in buildings, and for distributed water extraction in agricultural irrigation and emergency relief. The hygroscopic phase change capsule is applied to water-scarce areas, where liquid water is obtained by absorbing air water vapor at night and desorbing it under solar energy-driven desorption during the day.

9. The use of the hygroscopic phase change capsule for heat and humidity control and air water extraction as claimed in claim 8, characterized in that: The above application is realized through an adsorption-based air water extraction device, which is a transparent and closed structure. A hygroscopic phase change capsule layer is arranged on the upper layer and is laid on the filter plate. The lower layer is a water storage container. The top cover of the device is kept open at night, and the hygroscopic phase change capsules in the hygroscopic phase change capsule layer naturally absorb water vapor in the air. The top cover of the device is closed during the day. At this time, the device is in a closed condition. Solar energy heats the hygroscopic phase change capsules through the side wall of the device. At this time, the humidity in the device is extremely low. The hygroscopic phase change capsules lose their hygroscopic ability under extremely low humidity conditions, triggering the rupture of hydrogen bonds and van der Waals forces in the adsorbent, so that the adsorbed moisture is desorbed from the material as water vapor, and condensed into liquid water in the closed device through the gas-liquid separation structure.

10. The use of the hygroscopic phase change capsule for heat and humidity control and air water extraction according to claim 9, characterized in that: In the hygroscopic phase change capsule layer, the hygroscopic phase change capsules are evenly spread on the filter plate without stacking, ensuring that the material is fully exposed to sunlight.

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