A solar photothermal conversion phase change heat storage structure based on full-spectrum regulation and a preparation method thereof

Abstract

The present invention relates to the technical field of phase change heat storage, and specifically relates to a solar photothermal conversion phase change heat storage structure based on full-spectrum regulation and a preparation method thereof; it solves the problems of how to specifically apply to reduce the radiative heat dissipation on the material surface and how to reduce the radiative heat dissipation without affecting light absorption, including a photothermal conversion heat storage unit and a spectrum regulation unit. The spectrum regulation unit is integrally arranged on the upper surface of the photothermal conversion heat storage unit. The photothermal conversion heat storage unit is a photothermal conversion phase change material and is used for spontaneously performing photothermal conversion and heat storage on solar radiation. The spectrum regulation unit has different transmittances and reflectivities for different radiation bands; the photothermal conversion surface of the photothermal conversion heat storage unit shows a high absorption rate for solar radiation in the wavelength range of 0-2.5 μm, while showing a low emissivity in the infrared radiation band above 2.5 μm, reducing the radiative heat loss of the photothermal conversion phase change energy storage material while ensuring a high light absorption rate.

Description

Technical Field

[0001] The present invention relates to the technical field of phase change heat storage, and particularly relates to a solar photothermal conversion phase change heat storage structure based on full-spectrum regulation and a preparation method thereof. Background Art

[0002] Renewable energy is being used to replace fossil fuels to reduce greenhouse gas emissions; among the research hotspots of solar energy, the intermittency and periodicity of solar radiation and thermal storage are a major challenge. Due to these problems, a large number of studies hope to achieve the effective utilization of solar energy through photothermal conversion and phase change heat storage materials; photothermal conversion materials provide high energy conversion efficiency; currently, the photothermal conversion fillers applied to phase change materials are mainly divided into noble metal nanoparticles, carbon-based materials, organic molecular dyes, and semiconductor materials; however, since they cannot shield the illuminated surface, during the process of receiving solar radiation energy for storage, these materials also face the problem of heat dissipation to the outside; according to Kirchhoff's law, the absorption ability of an object is proportional to its radiation intensity. Having a very high absorption rate for solar radiation means that the material has a high emissivity in the thermal infrared band after heating. Therefore, the insulation measures have a crucial impact on the level of photothermal conversion efficiency. In the existing insulation measures, materials that reduce convection and radiation heat dissipation can be applied to the illuminated surface of the light-absorbing material. The current technical problems are: how to specifically apply materials that reduce radiation heat dissipation and how to reduce radiation and heat dissipation on the same surface without affecting light absorption. Summary of the Invention

[0003] In order to solve the above technical problems, the present invention provides a solar photothermal conversion phase change heat storage structure based on full-spectrum regulation and a preparation method thereof, so that the photothermal conversion surface of the photothermal conversion heat storage unit shows a high absorption rate for solar radiation within the wavelength range of 0-2.5 μm, and shows a low emissivity in the infrared radiation band above 2.5 μm, reducing the radiation heat loss of the photothermal conversion phase change energy storage material while ensuring a high photothermal absorption rate.

[0004] The technical solution of the present invention is specifically as follows:

[0005] A solar photothermal conversion phase change heat storage structure based on full-spectrum regulation, including a photothermal conversion heat storage unit and a spectrum regulation unit. The spectrum regulation unit is integrally arranged on the upper surface of the photothermal conversion heat storage unit. The photothermal conversion heat storage unit is a photothermal conversion phase change material and is used for spontaneously performing photothermal conversion and heat storage on solar radiation. The spectrum regulation unit can have different transmittance and reflectance for different bands.

[0006] Preferably, the emissivity of the spectrum regulation unit for infrared rays ≥ 80%, and the transmittance of the spectrum regulation unit for light ≥ 95%.

[0007] Preferably, the infrared band is above 2.5 μm, and the light transmission band is 0 - 2.5 μm.

[0008] Preferably, the spectral regulation unit is deposited on the surface of the photothermal conversion and heat storage unit after etching treatment by vacuum magnetron sputtering technology.

[0009] Preferably, the photothermal conversion and heat storage unit uses a composite shaped phase change material, and the phase change temperature of the shaped phase change material is higher than the temperature in the vacuum magnetron sputtering chamber.

[0010] Preferably, the composite shaped phase change material is prepared by compounding a three-dimensional photothermal conversion framework structure and a phase change material. The three-dimensional photothermal conversion framework structure includes, but is not limited to, one of wood carbon, hydrothermal graphene aerogel, carbon fiber / thermoplastic elastomer, and graphene / hydroxyethyl cellulose aerogel; the phase change material includes, but is not limited to, one of paraffin and polyethylene glycol.

[0011] A preparation method of a solar energy photothermal conversion and phase change heat storage structure based on full-spectrum regulation, used to prepare the above-mentioned solar energy photothermal conversion and phase change heat storage structure based on full-spectrum regulation, includes the following steps:

[0012] Step 1: Prepare a photothermal conversion and heat storage unit with photothermal conversion ability;

[0013] Step 2: Deposit a spectral regulation unit on the photothermal conversion and heat storage unit.

[0014] Preferably, the composite shaped phase change material is prepared by compounding a three-dimensional photothermal conversion framework structure and a phase change material. The three-dimensional photothermal conversion framework structure includes, but is not limited to, one of wood carbon, hydrothermal graphene aerogel, carbon fiber / thermoplastic elastomer, and graphene / hydroxyethyl cellulose aerogel; the phase change material includes, but is not limited to, one of paraffin and polyethylene glycol.

[0015] Preferably, in Step 2, vacuum magnetron sputtering technology is used for coating and depositing the spectral regulation unit, and the target materials used are partially highly doped semiconductors, including, but not limited to, indium tin oxide, indium oxide, tin oxide, and cadmium stannate.

[0016] Furthermore, an ITO thin film is prepared on the composite PCM substrate using magnetron sputtering technology. The sputtering target is a 99.99% ITO target, with a ratio of In2O3:SnO2 = 9:1, the working gas is 99.999% Ar, the flow rate is 30 Sccm, the power is 100 W, the bias voltage is 178 V, the sputtering temperature is room temperature, and the vacuum degree is 8.0×10 -4Pa; The target materials used in the vacuum magnetron sputtering technology are partially highly doped semiconductors, such as indium tin oxide, indium oxide, tin oxide, cadmium stannate, etc.; the thickness of the ITO film is 100 nm.

[0017] The preparation of the photothermal conversion and heat storage unit with photothermal conversion ability described in Step 1 includes the following steps:

[0018] Step 101: Prepare the photothermal conversion material;

[0019] Step 102: Prepare the photothermal conversion composite shaped phase change material;

[0020] Step 103: Etch the prepared photothermal conversion composite shaped phase change material.

[0021] Furthermore, the etching treatment of the photothermal conversion composite shaped phase change material is carried out by using the soluble solvent corresponding to the phase change material, so that the photothermal conversion material is exposed on the surface of the photothermal conversion and heat storage unit.

[0022] Furthermore, after the surface etching treatment of the photothermal conversion composite shaped phase change material, the solvent is completely volatilized.

[0023] Due to the adoption of the above technical solution, the beneficial effects of the present invention are as follows:

[0024] 1. This application directly uses the photothermal conversion composite shaped phase change material as the substrate for ITO coating. Through the integrated design of the photothermal conversion composite shaped phase change material and ITO coating, the loss of radiative heat is reduced from the root, and no additional spectral selection and maintenance structure is required in practical applications. Since the surface of the ITO deposited thin film coating needs to be flat and there is no phase change material, and the leakage of the phase change material will cause the shedding of the surface heat mirror film; therefore, this application uses a unique etching technology, combined with the vacuum magnetron sputtering coating technology of ITO coating, to improve the shape stability of the phase change material, solve the problem of uneven coating surface during ITO coating, and reduce the radiative heat dissipation of the phase change material to the environment without affecting light absorption, so as to achieve the purpose of improving the heat storage efficiency;

[0025] 2. In this application, through the vacuum magnetron sputtering coating technology, the target material is sputtered on the photothermal conversion and heat storage unit, the reflectivity of the thin film to infrared rays is ≥80%, and the transmittance of the spectral regulation unit to light is ≥95%;

[0026] 3. The photothermal conversion surface of the photothermal conversion and heat storage unit of this application shows a high absorption rate of solar radiation in the wavelength range of 0 - 2.5 μm, while showing a low emissivity in the infrared radiation band above 2.5 μm (ITO coating will increase the thermal reflectivity, thereby reducing the emissivity of the photothermal conversion and heat storage unit). While ensuring a high photothermal absorption rate, the radiative heat loss of the photothermal conversion phase change energy storage material is reduced. Brief Description of the Drawings

[0027] Figure 1 Technical implementation flowchart of the present invention;

[0028] Figure 2 Scanning electron microscope image of the coated surface of the material prepared in Example 1 of the method according to the present invention;

[0029] Figure 3 Reflectance curves of ITO-coated glass and ordinary glass;

[0030] Figure 4 Emissivity comparison between ITO-coated composite phase change material and uncoated phase change material in the infrared band;

[0031] Figure 5 Phase change temperature curves of ITO-coated composite phase change material and uncoated phase change material under a standard solar illumination. Detailed Implementation Manner

[0032] The present invention will be specifically described below in conjunction with specific embodiments. It is necessary to point out here that the following embodiments are only used for further illustration of the present invention and cannot be construed as limiting the protection scope of the present invention. Some non-essential improvements and adjustments made by those skilled in the art to the present invention based on the content of the present invention still fall within the protection scope of the present invention.

[0033] Example 1:

[0034] Preparation of the photothermal conversion and heat storage unit:

[0035] First, reduced graphene oxide is prepared by a hydrothermal reduction method. First, graphene oxide is dispersed in deionized water and ultrasonicated for 1 hour at room temperature; then, ascorbic acid is uniformly added to the graphene oxide solution (preferably 2 - 5 mg / ml), and the mass ratio of ascorbic acid to graphene oxide is 2:1; then, the mixture is sealed in a glass bottle and heated at 95 °C for 6 hours to obtain a reduced graphene oxide hydrogel. Next, the reduced graphene oxide hydrogel is cooled to room temperature and dialyzed in a 40% ethanol solution to remove unreacted reagents. Finally, the dialyzed reduced graphene oxide hydrogel can be freeze-dried at -60 °C for 48 hours to obtain a reduced graphene oxide aerogel.

[0036] A graphene-based composite phase change material is prepared by a vacuum impregnation method. The prepared reduced graphene oxide aerogel is placed in a liquid polyethylene glycol phase change material (phase change temperature of 50 °C) and put into a vacuum oven set at -0.1 MPa at 100 °C. The liquid polyethylene glycol continuously penetrates into the pore structure under negative pressure. After filling the reduced graphene oxide aerogel with the phase change material, the composite phase change material is taken out and cooled to room temperature.

[0037] In the solid state of the composite phase change material, the residual polyethylene glycol on the surface was washed off with water, and the composite PCM substrate was obtained by placing it in an oven at 20 °C for 6 h.

[0038] Depositing the spectral regulation unit on the photothermal conversion heat storage unit:

[0039] Using magnetron sputtering technology, an ITO thin film was prepared on the composite PCM substrate. The sputtering target was a 99.99% ITO target with a ratio of In203:Sn02 = 9:1. The working gas was 99.999% Ar with a flow rate of 30 Sccm, a power of 100 W, a bias voltage of 178 V, the sputtering temperature was room temperature, and the vacuum degree was 8.0×10 -4 Pa; the targets used in the vacuum magnetron sputtering technology are partially highly doped semiconductors, indium tin oxide, indium oxide, tin oxide, cadmium stannate, etc.; the thickness of the ITO thin film is 100 nm. [[ID=,11]]

[0040] Example 2

[0041] Different from Example 1, in this example, the preparation method of the photothermal conversion heat storage unit is as follows: First, prepare a delignified balsam wood sample. Weigh 20 g of NaOH and 12.6 g of Na2SO3 and add them to 200 mL of deionized water to prepare a delignifying solution with a concentration of 0.5 mol / L; Second, put the balsam wood into the delignifying solution and boil it for 12 h, and repeatedly wash it with hot deionized water until the solution color becomes lighter; Finally, put it into a vacuum freeze dryer and freeze it for 48 h, and vacuum dry it for 36 h to obtain a delignified balsam wood sample.

[0042] Put the balsam wood sample into a tubular furnace for carbonization treatment. The carbonization temperature is 300 °C, the heating rate is 2 °C / min, keep the temperature for 2 hours, and finally cool it to room temperature by natural cooling, and purge with nitrogen throughout the process to obtain a carbonized balsam wood sample.

[0043] Prepare a wood-based carbon photothermal conversion phase change material by vacuum impregnation method. The phase change material is paraffin with a phase change temperature of 45 °C; place the carbonized balsam wood sample in molten paraffin, impregnate it under vacuum at 60 °C for 3 hours, and take it out and let it stand until it reaches room temperature.

[0044] In the solid state of the composite phase change material, wash off the residual paraffin on the surface with petroleum ether, and place it in an oven at 20 °C for 6 h to obtain the composite PCM substrate.

[0045] Example 3

[0046] Different from Example 1, the preparation method of the photothermal conversion and heat storage unit in this example is as follows: First, weigh PW and melt it in a blast drying oven at 80 °C. After PW is completely in a molten state, pour it into a beaker in an oil bath at 180 °C, add SEBS, and stir at high speed until it is completely dissolved. Then add 3 wt% expanded graphite and stir slowly until the expanded graphite is evenly dispersed, and then pour it into a mold and cool it.

[0047] Take out the composite phase change material from the mold. In the solidified state, wash away the residual paraffin on the surface with petroleum ether, and place it in an oven at 20 °C for 6 h to obtain a composite PCM substrate.

[0048] Example 4

[0049] Different from the examples, the preparation method of the photothermal conversion and heat storage unit in this example is as follows: First, dissolve hydroxyethyl cellulose in deionized water and stir in a water bath at 30 °C to prepare a hydroxyethyl cellulose hydrogel with a concentration of 2 wt%. Then add graphene nanosheets to deionized water and perform ultrasonic dispersion with a concentration of 5 mg / ml. Under the conditions of a 30 °C water bath and magnetic stirring, add 5 ml of the graphene nanosheet dispersion to 45 ml of the hydroxyethyl cellulose hydrogel until it is stirred evenly, pour it into a mold, and dry it in a freeze dryer to obtain a graphene / hydroxyethyl cellulose aerogel.

[0050] The graphene-based composite phase change material is prepared by the vacuum impregnation method. Place the prepared reduced graphene oxide / hydroxyethyl cellulose aerogel in a liquid polyethylene glycol phase change material (phase change temperature is 50 °C), and put it into a vacuum oven set at -0.1 MPa at 100 °C. The liquid polyethylene glycol continuously penetrates into the pore structure under negative pressure. After filling the graphene / hydroxyethyl cellulose aerogel with the phase change material, take out the composite phase change material and cool it to room temperature.

[0051] In the solidified state of the composite phase change material, wash away the residual polyethylene glycol on the surface with water, and place it in an oven at 20 °C for 6 h to obtain a composite PCM substrate.

[0052] Table 1 below shows the detection data of different photothermal conversion composite shaped phase change materials in Examples 1 to 4:

[0053]

[0054] Figure 2 It is a scanning electron microscope image of the surface of the ITO film deposited on the graphene aerogel-based composite phase change material. It can be seen from the figure that the surface of the ITO film deposited on the graphene aerogel-based composite phase change material is smooth and flat, and can exhibit good spectral selection performance.

[0055] Figure 3In the range of 0.25 - 15 μm, the optical parameter comparison between the heat mirror glass and the ordinary glass shows that the spectrum of solar radiation is concentrated in the 0 - 0.25 μm band, and both have a high transmittance, which is beneficial to the light absorption and photothermal conversion of the material. However, when comparing the ordinary glass and the heat mirror glass, the heat mirror glass has a higher reflectivity. In the range of 2.5 - 15 μm, the reflectivity of the heat mirror glass is much greater than that of the ordinary glass.

[0056] Figure 4 It can be seen that there are significant differences in the emissivity of the material surface in the infrared band before and after depositing the ITO film. The ITO film can effectively reduce the infrared emissivity and thus reduce the reflective heat loss of the material.

[0057] Figure 5 For the detection diagram of Example 1, it can be observed that under an environmental temperature of 23 °C and a standard solar intensity of 1000 W / ㎡, the heat mirror graphene aerogel-based composite phase change material (PEG / rGOA / ITO) can reach a high temperature of 98 °C, while the graphene aerogel-based composite phase change material (PEG / rGOA) can only reach 84.7 °C.

Claims

1. A solar thermal conversion phase change heat storage structure based on full spectrum regulation, characterized in that: It includes a photothermal conversion and heat storage unit and a spectrum regulation unit. The spectrum regulation unit is integrated on the upper surface of the photothermal conversion and heat storage unit. The photothermal conversion and heat storage unit is a photothermal conversion phase change material and is used to spontaneously convert solar radiation into heat and store heat. The spectrum regulation unit can have different transmittance and reflectivity for different wavelengths. The spectrum control unit is deposited on the surface of the photothermal conversion heat storage unit after surface etching by vacuum magnetron sputtering technology; The photothermal conversion heat storage unit uses a composite shape-fixed phase change material, and the phase change temperature of the composite shape-fixed phase change material is higher than the temperature in the vacuum magnetron sputtering chamber; The composite shaped phase change material is prepared by combining a photothermal conversion three-dimensional skeleton structure and a phase change material. The photothermal conversion three-dimensional skeleton structure adopts one of hydrothermal graphene aerogel and graphene / hydroxyethyl cellulose aerogel; the phase change material adopts polyethylene glycol. The graphene-based composite phase change material is prepared by vacuum impregnation method, and the specific steps are as follows: The prepared photothermal conversion three-dimensional skeleton structure was placed in a liquid polyethylene glycol phase change material with a phase change temperature of 50°C and placed in a vacuum oven set at -0.1MPa at 100°C; after filling the photothermal conversion three-dimensional skeleton structure with polyethylene glycol, the composite phase change material was removed and cooled to room temperature; When the composite phase change material is in a solidified state, the polyethylene glycol residue on the surface is washed away with water, and the composite phase change material is placed in an oven at 20°C for 6 hours to obtain a composite shape-fixed phase change material. Depositing a spectrum control unit on the photothermal conversion and heat storage unit: ITO thin films were prepared on composite shaped phase change materials using magnetron sputtering technology. The sputtering target was 99.99% ITO target with a ratio of In2O3:SnO2=9:

1. The working gas was 99.999% Ar with a flow rate of 30 Sccm, a power of 100 W, a bias voltage of 178 V, a sputtering temperature of room temperature, and a vacuum degree of 8.0×10 -4 Pa; the thickness of the ITO film is 100 nm.

2. The solar thermal conversion phase change heat storage structure based on full spectrum regulation according to claim 1 is characterized in that: The reflectivity of the spectrum control unit to infrared rays is ≥80%, and the transmittance of the spectrum control unit to light is ≥95%.

3. The solar thermal conversion phase change heat storage structure based on full spectrum regulation according to claim 2 is characterized in that: The infrared ray has a wavelength range of 2.5 μm or more, and the light transmission wavelength range is 0-2.5 μm.

4. A method for preparing a solar thermal conversion phase change thermal storage structure based on full spectrum regulation, characterized in that: The method for preparing a solar thermal conversion phase change heat storage structure based on full spectrum regulation according to any one of claims 1 to 3 comprises the following steps: Step 1: Prepare a photothermal conversion heat storage unit with photothermal conversion capability; Step 2: Depositing a spectrum control unit on the photothermal conversion and heat storage unit.

5. The method for preparing a solar thermal conversion phase change thermal storage structure based on full spectrum regulation according to claim 4, characterized in that: In step 2, vacuum magnetron sputtering technology is used to deposit the coating of the spectrum control unit, and the target material used is a partially highly doped semiconductor.

6. The method for preparing a solar thermal conversion phase change thermal storage structure based on full spectrum regulation according to claim 5, characterized in that: The preparation of the photothermal conversion heat storage unit with photothermal conversion capability described in step 1 comprises the following steps: Step 101: preparing a light-to-heat conversion material; Step 102: preparing a light-to-heat conversion composite shaped phase change material; Step 103: Etching the prepared photothermal conversion composite shaped phase change material.

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