Preparation method of low-water-evaporation-enthalpy aerogel and thermoelectric module water and electricity cogeneration system

Abstract

The invention relates to the field of preparation of photo-thermal water-power cogeneration devices, in particular to a preparation method of a low-water evaporation enthalpy aerogel and thermoelectric module water-power cogeneration system, which comprises the following steps: in an upper photo-thermal conversion area, covering a hot end of a thermoelectric module with a hydrophobic coating prepared from a multi-walled carbon nanotube and polydimethylsiloxane for heating; an aluminum radiator with good thermal conductivity is used below the thermoelectric module, and heat is transferred to an evaporation area. The lower part of the system is aerogel prepared by crosslinking chitosan and waterborne polyurethane, so that the evaporation enthalpy is reduced, effective evaporation is realized, and heat is taken away to reduce the temperature of a cold end. The multi-stage energy utilization can synergistically improve the power generation efficiency and the evaporation efficiency.

Description

Technical Field

[0001] The invention relates to the field of preparation of solar-thermal-water-electricity cogeneration devices, and specifically to a method for preparing a low water evaporation enthalpy aerogel and thermoelectric module water-electricity cogeneration system. Background Art

[0002] Water and electricity are undoubtedly important components of modern society. However, over-dependence on non-renewable resources has led to severe water shortages and major challenges in electricity production. Solar energy has attracted much attention due to its inexhaustible, inexhaustible and sustainable characteristics, and plays an important role in producing green electricity and promoting clean water production. Therefore, it is crucial to develop an energy conversion system that can achieve the dual functions of water evaporation and power generation using solar energy.

[0003] Photothermal conversion is the first step in the utilization of solar energy. At present, researchers have made great progress in finding and studying photothermal conversion materials, such as carbon materials, semiconductor materials, and metal nanomaterials. However, an often overlooked problem is that although these materials have excellent light absorption properties, contact with water will lead to a decrease in temperature because the absorbed energy is used to increase the water temperature. This greatly hinders the performance of the hot end of the thermoelectric module. This problem can be solved by using a hydrophobic photothermal layer to maximize the generated temperature. In addition, the hydrophobic photothermal layer is conducive to surface cleanliness and maintains excellent photothermal conversion performance.

[0004] In addition to improving the efficiency of photothermal conversion, the rate of steam generation is increased when it is confined to the air-water interface. Aerogels can significantly improve the evaporation of water, but their mechanical strength may not be able to support more demanding application scenarios. Polyurethane has excellent resilience and can be used to improve the mechanical strength of composite aerogels. This property is especially important in hydropower cogeneration equipment because it can support the weight of thermoelectric modules and heat sinks. Summary of the invention

[0005] The object of the present invention is to provide a method for preparing a low water evaporation enthalpy aerogel and a thermoelectric module water-power cogeneration system to solve the problems raised in the above background technology.

[0006] To achieve the above object, the present invention provides the following technical solution: a method for preparing a low water evaporation enthalpy aerogel and thermoelectric module water-power cogeneration system, comprising the following steps: Step 1, using multi-walled carbon nanotubes and polydimethylsiloxane to prepare light-absorbing ink; Step 2, spin coating the prepared light-absorbing ink on the hot end of the thermoelectric module by spin coating, that is, preparing the multi-walled carbon nanotube photothermal coating by spin coating; Step 3, mixing and cross-linking the aqueous polyurethane and chitosan solution to obtain a precursor solution; Step 4, freeze-drying the prepared precursor solution to obtain a composite aerogel; Step 5: placing the prepared composite aerogel under the heat sink at the cold end of the thermoelectric module in step 2, and then assembling it with the thermal conductive sheet to obtain a water-power cogeneration system.

[0007] Preferably, in step 1 and step 2, the multi-walled carbon nanotubes and SYLGARD 184 are mixed and ultrasonicated; then, the light-absorbing ink is spin-coated on the hot end of the thermoelectric module and cured in an oven.

[0008] Preferably, the mass percentage of the multi-walled carbon nanotubes and SYLGARD 184 is 0-12 wt %; the ultrasonic time is 30 minutes; and the curing temperature and time are 70° C. and 1 hour, respectively.

[0009] Preferably, in step 3, chitosan powder is added to a 2% acetic acid solution and stirred to completely dissolve it; then the aqueous polyurethane emulsion is stirred and diluted, and the chitosan solution is slowly added during the stirring process to mix it evenly; the resulting mixture is poured into a mold and a cross-linking agent is added, specifically, the cross-linking agent used is glutaraldehyde.

[0010] Preferably, the aqueous polyurethane emulsion is diluted to 15%; the volume ratio of the chitosan solution to the polyurethane emulsion is one of 2:1, 1:1, and 1:2; and the amount of the cross-linking agent used is 20 mg / ml.

[0011] Preferably, the specific preparation method in step 4 is: placing the completely cross-linked precursor solution on a copper block and directionally freezing it with liquid nitrogen; finally, freeze-drying, wherein the freeze-drying temperature and pressure are -50°C and 1Pa.

[0012] Preferably, the specific preparation method of step 5 is as follows: assembling the prepared thermoelectric module with photothermal coating, thermal conductive sheet and polyurethane chitosan composite aerogel; wherein thermal conductive silicone grease is coated between the thermoelectric module and the thermal conductive sheet to isolate the air and increase thermal conductivity.

[0013] Compared with the prior art, the present invention has the following beneficial effects: In the upper light-to-heat conversion zone, the present invention covers the hot end of the thermoelectric module with a hydrophobic coating made of multi-walled carbon nanotubes and polydimethylsiloxane for heating; an aluminum heat sink with good thermal conductivity is used under the thermoelectric module to transfer heat to the evaporation zone. The lower part of the system is an aerogel made of cross-linked chitosan and aqueous polyurethane to reduce the evaporation enthalpy and effectively evaporate, taking away heat to reduce the temperature of the cold end. This multi-stage energy utilization can synergistically improve the efficiency of power generation and evaporation. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1(a) Schematic diagram of manufacturing multi-walled carbon nanotube-coated thermoelectric module; (b) Schematic diagram of preparation of chitosan and waterborne polyurethane composite aerogel (PCA); Figure 2 (a) Photos of the thermoelectric module before (left) and after (CTEM, right) coating the photothermal layer; (b) SEM image of the side of the photothermal coating (attached picture: enlarged image of the surface of the photothermal layer); (c) TEM and CTEM reflection spectra in the wavelength range of 200~2500 nm (attached picture: absorption spectrum of CTEM); (d) SEM images of PCA from the side and (e) from the top; (f) The water contact angle of PCA is 0°; (g) PCA shows excellent water absorption performance when placed in methylene blue dye; Figure 3 (a) FTIR spectra of PUA, CSA and PCA (PUA is waterborne polyurethane aerogel and CSA is chitosan aerogel); (b) XPS spectrum of PCA; (c) thermogravimetric analysis curve; (d) compressive stress-strain characterization; (e) cyclic compression test of PCA; (f) photos of PCA compression and rapid recovery process; Figure 4 (a) Raman spectrum of pure water and (b) fitting curve of OH stretching mode energy region of water in PCA (fitting peaks based on Gaussian function represent intermediate water and free water); (c) DSC test curves of pure water and water in PCA; (d) Distribution of different types of water such as IW, FW, BW in PCA evaporator and schematic diagram of evaporation mechanism; (e) Comparison of dark evaporation rate and evaporation enthalpy within 1 hour; Figure 5 (a) Temperature distribution of hot and cold sides of CTEM, A-CTEM, C-CTEM and AC-CTEM systems under 1 sun illumination (A-CTEM is the assembly system of aerogel and thermoelectric module, C-CTEM is the assembly system of heat sink and thermoelectric module, AC-CTEM is the cogeneration system); (b) open circuit voltage of each system within 1 hour; (c) current-voltage curve; (d) power density; (e) cogeneration performance of AC-CTEM under different light intensities. DETAILED DESCRIPTION

[0015] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0016] See also Figure 1-5The present invention provides a technical solution: a method for preparing a low water evaporation enthalpy aerogel and a thermoelectric module water-power cogeneration system, comprising the following steps: Step 1, using multi-walled carbon nanotubes and polydimethylsiloxane to prepare light-absorbing ink; Step 2, spin coating the prepared light-absorbing ink on the hot end of the thermoelectric module by spin coating, that is, preparing the multi-walled carbon nanotube photothermal coating by spin coating; Step 3, mixing and cross-linking the aqueous polyurethane and chitosan solution to obtain a precursor solution; Step 4, freeze-drying the prepared precursor solution to obtain a composite aerogel; Step 5: placing the prepared composite aerogel under the heat sink at the cold end of the thermoelectric module in step 2, and then assembling it with the thermal conductive sheet to obtain a water-power cogeneration system.

[0017] Furthermore, in step 1 and step 2, the multi-walled carbon nanotubes and SYLGARD 184 are mixed and ultrasonicated; then, the light absorbing ink is spin-coated on the hot end of the thermoelectric module and cured in an oven.

[0018] Furthermore, the mass percentage of multi-walled carbon nanotubes and SYLGARD 184 is 0-12 wt %; the ultrasonic time is 30 minutes; and the curing temperature and time are 70° C. and 1 hour, respectively.

[0019] Furthermore, in step 3, chitosan powder is added to a 2% acetic acid solution and stirred to completely dissolve it; then the aqueous polyurethane emulsion is stirred and diluted, and the chitosan solution is slowly added during the stirring process to mix it evenly; the resulting mixture is poured into a mold and a cross-linking agent is added, specifically, the cross-linking agent used is glutaraldehyde.

[0020] Furthermore, the aqueous polyurethane emulsion is diluted to 15%; the volume ratio of the chitosan solution to the polyurethane emulsion is one of 2:1, 1:1, and 1:2; and the amount of the cross-linking agent used is 20 mg / ml.

[0021] Furthermore, the specific preparation method in step 4 is: placing the completely cross-linked precursor solution on a copper block and directionally freezing it with liquid nitrogen; finally, freeze-drying, wherein the freeze-drying temperature and pressure are -50°C and 1Pa.

[0022] Furthermore, the specific preparation method of step 5 is as follows: assembling the prepared thermoelectric module with photothermal coating, thermal conductive sheet and polyurethane chitosan composite aerogel; wherein thermal conductive silicone grease is coated between the thermoelectric module and the thermal conductive sheet to isolate the air and increase thermal conductivity.

[0023] Specifically, SYLGARD 184 was purchased from The Dow Chemical Company, multi-walled carbon nanotubes were purchased from Nanjing Pioneer Nanomaterials Technology Co., Ltd., commercial thermoelectric modules (4 cm in length and 4 cm in width) were purchased from Guangzhou Sairui Electronic Technology Co., Ltd., chitosan was purchased from China National Pharmaceutical Group Chemical Reagent Co., Ltd., and waterborne polyurethane (solid content 60%) was purchased from Shanghai McLean Biochemical Technology Co., Ltd. All chemicals were of reagent grade and used without further purification.

[0024] First, 9 wt% of multi-walled carbon nanotubes were mixed into SYLGARD 184 (wherein the weight ratio of PDMS prepolymer to curing agent was 10:1) and ultrasonically treated for 30 minutes to make it evenly mixed; then it was spin-coated on the hot end of the thermoelectric module and cured at 70°C for 1 hour to obtain a thermoelectric module covered with multi-walled carbon nanotubes.

[0025] Secondly, add 2g of chitosan powder to 98ml of 2% acetic acid solution and stir to form a uniform solution; then dilute the polyurethane emulsion to 15%; take 15ml of the diluted polyurethane emulsion, slowly add 15ml of chitosan solution during stirring until the mixture is uniform; pour the resulting mixture into a mold, add a cross-linking agent (GA, 20mg / ml); place the mold containing the precursor solution on a copper block and directionally freeze it with liquid nitrogen; then sublimate and dry it in a vacuum freeze dryer at -50℃ to complete the preparation.

[0026] The prepared thermoelectric module with photothermal coating, thermal conductive sheet and polyurethane chitosan composite aerogel were assembled layer by layer to obtain a water and power cogeneration system, wherein thermal conductive silicone grease (Honeywell PTM7950) was coated between the thermoelectric module and the thermal conductive sheet to isolate the air and increase thermal conductivity.

[0027] In the present invention, a hydrophobic coating made of multi-walled carbon nanotubes and polydimethylsiloxane is covered on the hot end of the thermoelectric module in the upper light-to-heat conversion zone for heating; an aluminum heat sink with good thermal conductivity is used under the thermoelectric module to transfer heat to the evaporation zone. The lower part of the system is an aerogel made of cross-linked chitosan and water-based polyurethane to reduce the evaporation enthalpy and effectively evaporate, taking away heat to reduce the temperature of the cold end. This multi-stage energy utilization can synergistically improve the efficiency of power generation and evaporation.

[0028] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a low water evaporation enthalpy aerogel and thermoelectric module water and power cogeneration system, characterized in that: The following steps are involved: Step 1, using multi-walled carbon nanotubes and polydimethylsiloxane to prepare light-absorbing ink; Step 2, spin coating the prepared light-absorbing ink on the hot end of the thermoelectric module by spin coating, that is, preparing the multi-walled carbon nanotube photothermal coating by spin coating; Step 3, mixing and cross-linking the aqueous polyurethane and chitosan solution to obtain a precursor solution; Step 4, freeze-drying the prepared precursor solution to obtain a composite aerogel; Step 5: placing the prepared composite aerogel under the heat sink at the cold end of the thermoelectric module in step 2, and then assembling it with the thermal conductive sheet to obtain a water-power cogeneration system.

2. The method for preparing a low water evaporation enthalpy aerogel and thermoelectric module water and power cogeneration system according to claim 1, characterized in that: In the steps 1 and 2, the multi-walled carbon nanotubes and SYLGARD 184 are mixed and ultrasonicated; then, the light-absorbing ink is spin-coated on the hot end of the thermoelectric module and cured in an oven.

3. The method for preparing a low water evaporation enthalpy aerogel and thermoelectric module water and power cogeneration system according to claim 2, characterized in that: The mass percentage of the multi-walled carbon nanotubes and SYLGARD 184 is 0-12 wt %; the ultrasonic time is 30 minutes; and the curing temperature and time are 70° C. and 1 hour, respectively.

4. The method for preparing a low water evaporation enthalpy aerogel and thermoelectric module water and power cogeneration system according to claim 1, characterized in that: In step 3, chitosan powder is added to a 2% acetic acid solution and stirred to completely dissolve; then the aqueous polyurethane emulsion is stirred and diluted, and the chitosan solution is slowly added during the stirring process to mix it evenly; the resulting mixture is poured into a mold and a crosslinking agent is added, specifically, the crosslinking agent used is glutaraldehyde.

5. The method for preparing a low water evaporation enthalpy aerogel and thermoelectric module water and power cogeneration system according to claim 1, characterized in that: The aqueous polyurethane emulsion is diluted to 15%; the volume ratio of the chitosan solution to the polyurethane emulsion is one of 2:1, 1:1, and 1:2; and the amount of the cross-linking agent used is 20 mg / ml.

6. The method for preparing a low water evaporation enthalpy aerogel and thermoelectric module water and power cogeneration system according to claim 1, characterized in that: The specific preparation method in step 4 is as follows: placing the completely cross-linked precursor solution on a copper block and directionally freezing it with liquid nitrogen; and finally, freeze-drying, wherein the freeze-drying temperature and pressure are -50°C and 1Pa.

7. The method for preparing a low water evaporation enthalpy aerogel and thermoelectric module water and power cogeneration system according to claim 1, characterized in that: The specific preparation method of step 5 is as follows: assembling the prepared thermoelectric module with photothermal coating, thermal conductive sheet and polyurethane chitosan composite aerogel; wherein thermal conductive silicone grease is applied between the thermoelectric module and the thermal conductive sheet to isolate the air and increase thermal conductivity.

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