Preparation method of low water vaporization enthalpy aerogel and thermoelectric module water and power cogeneration system

Abstract

This invention relates to the preparation of solar-thermal-water-power cogeneration devices, specifically a method for preparing a low-water-evaporation-enthalpy aerogel and thermoelectric module cogeneration system. In the upper photothermal conversion zone, a hydrophobic coating made of multi-walled carbon nanotubes and polydimethylsiloxane is applied to the hot end of the thermoelectric module to provide heat. A highly conductive aluminum heat sink is located beneath the thermoelectric module to transfer heat to the evaporation zone. The lower portion of the system comprises an aerogel made of cross-linked chitosan and water-based polyurethane, which reduces the evaporation enthalpy and effectively evaporates, removing heat to lower the temperature at the cold end. This multi-stage energy utilization synergistically improves power generation and evaporation efficiency.

Description

Technical Field

[0001] The present invention relates to the field of preparation of solar-thermal-electricity cogeneration devices, and in particular 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 essential components of modern society. However, overreliance on non-renewable resources has led to severe water shortages and significant challenges in electricity production. Solar energy, garnering significant attention for its inexhaustible, sustainable nature, plays a crucial role in generating green electricity and promoting clean water production. Therefore, developing an energy conversion system that utilizes solar energy for both water evaporation and electricity generation is crucial.

[0003] Photothermal conversion is the first step in harnessing solar energy. Researchers have made significant progress in identifying and researching materials for photothermal conversion, such as carbon materials, semiconductor materials, and metal nanomaterials. However, an often-overlooked issue is that while these materials have excellent light absorption properties, contact with water results in a decrease in temperature because the absorbed energy is used to raise the water temperature. This significantly hinders the performance of the hot end of the thermoelectric module. This problem can be addressed by using a hydrophobic photothermal layer to maximize the generated temperature. Furthermore, a hydrophobic photothermal layer facilitates surface cleanliness and maintains excellent photothermal conversion performance.

[0004] In addition to improving photothermal conversion efficiency, steam generation is accelerated when confined to the air-water interface. Aerogels can significantly enhance water evaporation, but their mechanical strength may not support more demanding applications. Polyurethane exhibits excellent resilience and can be used to enhance the mechanical strength of composite aerogels. This property is particularly important in hydropower cogeneration systems, as it supports 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 vaporization 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 objectives, the present invention provides the following technical solution: a method for preparing a low water vaporization enthalpy aerogel and thermoelectric module water and power cogeneration system, comprising the following steps:

[0007] Step 1: preparing light-absorbing ink using multi-walled carbon nanotubes and polydimethylsiloxane;

[0008] Step 2: Spin-coating the prepared light-absorbing ink onto the hot end of the thermoelectric module by spin coating. That is, a multi-walled carbon nanotube photothermal coating is prepared by spin coating. The multi-walled carbon nanotubes and SYLGARD 184 are mixed and ultrasonicated. Then, the light-absorbing ink is spin-coated onto the hot end of the thermoelectric module and cured in an oven. The mass percentage of the multi-walled carbon nanotubes and SYLGARD 184 is 0-12 wt %. The ultrasonication time is 30 minutes. The curing temperature and time are 70° C. and 1 hour, respectively.

[0009] Step 3: Mixing and cross-linking aqueous polyurethane and chitosan solutions to form a precursor solution; specifically, adding chitosan powder to a 2% acetic acid solution and stirring to completely dissolve it; then stirring and diluting the aqueous polyurethane emulsion, and slowly adding the chitosan solution during the stirring process to mix it evenly; pouring the resulting mixture into a mold and adding a crosslinking agent, specifically glutaraldehyde; diluting the aqueous polyurethane emulsion 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 crosslinking agent used is 20 mg / ml;

[0010] Step 4: freeze-drying the prepared precursor solution to obtain a composite aerogel;

[0011] Step 5: Place the prepared composite aerogel under the heat sink at the cold end of the thermoelectric module in step 2, and then assemble it with the thermal conductive sheet to obtain a water and power cogeneration system.

[0012] 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 it, wherein the freeze-drying temperature and pressure are -50°C and 1Pa.

[0013] 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.

[0014] Compared with existing technologies, this invention offers the following advantages: In the upper photothermal conversion zone, a hydrophobic coating made of multi-walled carbon nanotubes and polydimethylsiloxane covers the hot end of the thermoelectric module to provide heat. A highly conductive aluminum heat sink is located beneath the module to transfer heat to the evaporation zone. The lower portion of the system utilizes an aerogel made of cross-linked chitosan and water-based polyurethane to reduce evaporation enthalpy and effectively evaporate, removing heat and lowering the temperature at the cold end. This multi-stage energy utilization synergistically improves power generation and evaporation efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1(a) Schematic diagram of the fabrication of a multi-walled carbon nanotube-coated thermoelectric module; (b) Schematic diagram of the preparation of chitosan and waterborne polyurethane composite aerogel (PCA);

[0016] Figure 2 (a) Photographs of the thermoelectric module before (left) and after (CTEM, right) coating with a photothermal layer; (b) SEM image of the side of the photothermal coating (attached image: magnified image of the photothermal layer surface); (c) TEM and CTEM reflection spectra in the wavelength range of 200-2500 nm (attached image: CTEM absorption spectrum); (d) SEM images of the PCA from the side and (e) from the top; (f) The water contact angle of PCA is 0°; (g) PCA exhibits excellent water absorption properties when placed in methylene blue dye;

[0017] 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 the compression and rapid recovery process of PCA;

[0018] Figure 4 (a) Raman spectrum of pure water and (b) fitting curve of the OH stretching mode energy region of water in PCA (the fitting peaks based on the Gaussian function represent intermediate water and free water); (c) DSC test curves of pure water and water in PCA; (d) Schematic diagram of the distribution of different types of water, such as IW, FW, and BW, in the PCA evaporator and the evaporation mechanism; (e) Comparison of dark evaporation rate and evaporation enthalpy within 1 hour;

[0019] Figure 5 (a) Temperature distribution diagram of the 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, and 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

[0020] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. 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 making creative efforts are within the scope of protection of the present invention.

[0021] See also Figure 1-5 The present invention provides a technical solution: a method for preparing a low water vaporization enthalpy aerogel and thermoelectric module water and power cogeneration system, comprising the following steps:

[0022] Step 1: preparing light-absorbing ink using multi-walled carbon nanotubes and polydimethylsiloxane;

[0023] Step 2: Spin-coating the prepared light-absorbing ink onto the hot end of the thermoelectric module by spin coating. That is, a multi-walled carbon nanotube photothermal coating is prepared by spin coating. The multi-walled carbon nanotubes and SYLGARD 184 are mixed and ultrasonicated. Then, the light-absorbing ink is spin-coated onto the hot end of the thermoelectric module and cured in an oven. The mass percentage of the multi-walled carbon nanotubes and SYLGARD 184 is 0-12 wt %. The ultrasonication time is 30 minutes. The curing temperature and time are 70° C. and 1 hour, respectively.

[0024] Step 3: Mixing and cross-linking aqueous polyurethane and chitosan solutions to form a precursor solution; specifically, adding chitosan powder to a 2% acetic acid solution and stirring to completely dissolve it; then stirring and diluting the aqueous polyurethane emulsion, and slowly adding the chitosan solution during the stirring process to mix it evenly; pouring the resulting mixture into a mold and adding a crosslinking agent, specifically glutaraldehyde; diluting the aqueous polyurethane emulsion 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 crosslinking agent used is 20 mg / ml;

[0025] Step 4: freeze-drying the prepared precursor solution to obtain a composite aerogel;

[0026] Step 5: Place the prepared composite aerogel under the heat sink at the cold end of the thermoelectric module in step 2, and then assemble it with the thermal conductive sheet to obtain a water and power cogeneration system.

[0027] Furthermore, 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; finally, freeze-drying it, wherein the freeze-drying temperature and pressure are -50°C and 1Pa.

[0028] 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.

[0029] 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 water-based polyurethane (solid content 60%) was purchased from Shanghai MacLean Biochemical Technology Co., Ltd. All chemicals were reagent grade and used without further purification.

[0030] First, 9 wt% of multi-walled carbon nanotubes were mixed into SYLGARD 184 (where the weight ratio of PDMS prepolymer to curing agent was 10:1) and ultrasonically treated for 30 minutes to ensure uniform mixing. The mixture was then 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.

[0031] Secondly, 2g of chitosan powder was added to 98ml of 2% acetic acid solution and stirred to form a uniform solution; the polyurethane emulsion was then diluted to 15%; 15ml of the diluted polyurethane emulsion was slowly added to 15ml of the chitosan solution while stirring until the mixture was uniform; the resulting mixture was poured into a mold, and a cross-linking agent (GA, 20mg / ml) was added; the mold containing the precursor solution was placed on a copper block and directionally frozen with liquid nitrogen; and then sublimation drying was completed in a vacuum freeze dryer at -50°C to complete the preparation.

[0032] 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 grease (Honeywell PTM7950) was coated between the thermoelectric module and the thermal conductive sheet to isolate the air and increase thermal conductivity.

[0033] In this invention, a hydrophobic coating made of multi-walled carbon nanotubes and polydimethylsiloxane is applied to the hot end of the thermoelectric module in the upper photothermal conversion zone to provide heat. A highly conductive aluminum heat sink is located beneath the module to transfer heat to the evaporation zone. The lower portion of the system utilizes an aerogel made of cross-linked chitosan and water-based polyurethane to reduce evaporation enthalpy and facilitate efficient evaporation, removing heat and lowering the temperature at the cold end. This multi-stage energy utilization synergistically improves power generation and evaporation efficiency.

[0034] While 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 these embodiments without departing from the principles and spirit of the invention, and that the scope of the invention is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a low water vaporization enthalpy aerogel and thermoelectric module water and power cogeneration system, characterized in that: The following steps are involved: Step 1: preparing light-absorbing ink using multi-walled carbon nanotubes and polydimethylsiloxane; Step 2: Spin-coating the prepared light-absorbing ink onto the hot end of the thermoelectric module by spin coating. That is, a multi-walled carbon nanotube photothermal coating is prepared by spin coating. The multi-walled carbon nanotubes and SYLGARD 184 are mixed and ultrasonicated. Then, the light-absorbing ink is spin-coated onto the hot end of the thermoelectric module and cured in an oven. The mass percentage of the multi-walled carbon nanotubes and SYLGARD 184 is 0-12 wt %. The ultrasonication time is 30 minutes. The curing temperature and time are 70° C. and 1 hour, respectively. Step 3: Mixing and cross-linking aqueous polyurethane and chitosan solutions to form a precursor solution; specifically, adding chitosan powder to a 2% acetic acid solution and stirring to completely dissolve it; then stirring and diluting the aqueous polyurethane emulsion, and slowly adding the chitosan solution during the stirring process to mix it evenly; pouring the resulting mixture into a mold and adding a crosslinking agent, specifically glutaraldehyde; diluting the aqueous polyurethane emulsion 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 crosslinking agent used is 20 mg / ml; Step 4: freeze-drying the prepared precursor solution to obtain a composite aerogel; Step 5: Place the prepared composite aerogel under the heat sink at the cold end of the thermoelectric module in step 2, and then assemble it with the thermal conductive sheet to obtain a water and power cogeneration system.

2. The method for preparing a low water vaporization 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; finally, freeze-drying it, wherein the freeze-drying temperature and pressure are -50°C and 1Pa.

3. The method for preparing a low water vaporization 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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