Selective radiation refrigeration sponge for efficient refrigeration and preparation method thereof

Abstract

The invention discloses selective radiation refrigeration sponge for efficient refrigeration and a preparation method of the selective radiation refrigeration sponge, and belongs to the field of thermal management materials. The selective radiation refrigeration sponge is prepared through a low-temperature precipitation method and a solvent exchange method, the obtained sponge is composed of micron-sized particles, the particles are connected with one another to form a block, and the block has high porosity. The sponge has the characteristics of high solar spectral reflectivity, selective infrared emissivity and low thermal conductivity, and can realize efficient refrigeration; and due to the mutual adhesion characteristic of the internal particles, the material has higher mechanical strength, and is an ideal thermal management material suitable for buildings and the like. The preparation method is simple, feasible, safe, reliable and suitable for large-scale application.

Description

Technical Field

[0001] The invention relates to the field of building thermal management, and in particular to a thermal management material for efficient refrigeration and a preparation method thereof. The efficient refrigeration effect is due to the infrared radiation selectivity and low thermal conductivity characteristics of the sponge. Background Art

[0002] Buildings are exposed to sunlight and absorb a large amount of solar radiation and ambient infrared radiation, which causes active thermal management technology to consume a lot of energy and is accompanied by a large amount of greenhouse gas emissions. The establishment of passive thermal management technology will effectively alleviate this situation. Radiative cooling technology has received widespread attention in recent years. It passively reduces the temperature of outdoor objects such as buildings by reflecting almost all sunlight and enhancing infrared emission from atmospheric windows (8-13 μm) to achieve the purpose of reducing thermal management energy consumption. From the basic heat dissipation equation: P Cool (T)=P Rad (T)-P Atm (T Amb )-P Sun -P Cond+Conv (T) Where P Cool (T) is the radiation cooling power density, P Rad (T) is the infrared radiation power density of the object, P Atm (T Amb ) is the atmospheric infrared radiation power density, P Sun is the absorbed solar radiation power density, P Cond+Conv (T) is the power density of heat entering the object from the air through heat conduction and heat convection, T is the temperature of the object, T Amb It is room temperature.

[0003] When the radiation cooling material has selective infrared emissivity and low thermal conductivity (i.e., it has high infrared emissivity only at the atmospheric window, and the non-atmospheric window area reduces atmospheric infrared radiation due to low infrared emissivity (i.e., P Atm (T Amb )) absorption, low thermal conductivity can reduce the ambient heat intrusion into the material through convection and conduction), and the refrigeration performance is further improved.

[0004] Selective radiation refrigeration materials reported in existing literature, such as polyoxymethylene, polyethylene oxide, silicon oxide, etc., have fewer infrared resonance modes due to the presence of molecular structures with good symmetry inside, and they show the characteristics of selective infrared emission. In order to meet the characteristics of high solar spectrum reflectivity, the preparation methods of these materials are usually based on electrostatic spinning or coating. For example, the patent document with publication number CN116790087A discloses a selective infrared emitting material based on polyoxymethylene and polytetrafluoroethylene, which is prepared by an electrostatic spinning process and is used to improve the refrigeration effect. For example, the patent document with announcement number CN113513858A discloses a selective infrared emitting ceramic coating for improving the cooling effect. Objectively speaking, these materials can meet the characteristics of high solar spectrum and selective infrared emission of radiation refrigeration, but cannot take into account the characteristics of low thermal conductivity. Summary of the invention

[0005] The purpose of the present invention is to provide a radiative cooling material with high solar spectrum reflectivity, selective infrared emission and low thermal conductivity, which can effectively achieve passive cooling and further improve the cooling effect, so that the building surface can achieve a lower temperature state, thereby reducing the use of indoor active thermal management equipment.

[0006] To achieve the above-mentioned purpose, the present invention provides a method for preparing a selective radiation sponge by a low-temperature precipitation method and a solvent exchange method, and constructs a sponge with functional integrity and improved refrigeration effect, which has both selective infrared emissivity, high solar spectrum reflectivity, and low thermal conductivity, and is used for efficient building refrigeration. The sponge has the characteristics of selective infrared emissivity and low thermal conductivity, that is, it has a high infrared emissivity only at the atmospheric window, and the non-atmospheric window area reduces the absorption of ambient infrared radiation due to the low infrared emissivity. The low thermal conductivity can reduce the intrusion of ambient heat into the material through convection and conduction, thereby achieving efficient refrigeration.

[0007] Specifically, the present invention provides a selective radiation cooling sponge for high-efficiency cooling applications, and the preparation method thereof includes: 1) dissolving the selective infrared emitting polymer in a benign solvent to form a uniform solution; 2) placing the uniform solution obtained in step 1) in a low temperature environment so that the benign solvent is converted into a solid state, and then the polymer is precipitated from the solvent to form a block composed of polymer-solid solvent; 3) The block formed in step 2) is directly immersed in a poor solvent in a low temperature environment, so that the good solvent molecules in the block are dissolved in the poor solvent, and then completely transformed into a gel block composed of a polymer and a poor solvent, and then dried to obtain a selective radiation cooling sponge.

[0008] The selective radiation refrigeration sponge preparation process is a low temperature precipitation method and a solvent exchange method ( Figure 1), wherein the benign solvent and the poor solvent are for the selective infrared emitting polymer. The selective infrared emitting polymer in step 1), such as polyoxymethylene, polyethylene oxide, etc., is dissolved in a benign solvent, the dissolution temperature is maintained in the range of 45°C-80°C, and the dissolution concentration is 6%-12% by mass. For polyoxymethylene, its benign solvent is, for example, hexafluoroisopropanol; for polyethylene oxide, its benign solvent is, for example, deionized water, ethanol.

[0009] In the above step 2), preferably, the obtained uniform solution is placed in a low temperature environment of -16°C to -5°C, so that the benign solvent is converted into a solid state, and then the polymer is precipitated from the solvent to form a block composed of polymer-solid solvent.

[0010] In the above step 3), preferably, the block is immersed in a poor solvent with a freezing point lower than -16°C, so that the good solvent molecules in the block are dissolved in the poor solvent. After immersion for 2-3 days, the block material is completely transformed into a gel block composed of polymer and poor solvent, and then dried in an oven at 60°C-100°C at normal pressure. The freezing point of the poor solvent is lower than -16°C, such as ethanol, tetrahydrofuran, N,N-dimethylformamide (DMF), etc.

[0011] The sponge obtained by the present invention is composed of micron-sized particles, which are connected to form a block and have a high porosity. The microstructure of the sponge forms a strong Mie scattering effect, thereby forming a high solar spectrum reflectivity; the strong symmetry of its molecular structure forms a selective infrared emissivity, and has a high infrared emissivity at the atmospheric window (8-13μm); the porous structure of the sponge forms the characteristics of low thermal conductivity.

[0012] The selective radiation cooling sponge prepared by the low-temperature precipitation method and the solvent exchange method has the characteristics of high solar spectrum reflectivity, selective infrared emissivity, and low thermal conductivity, and can achieve efficient cooling; and due to the mutual adhesion of internal particles, it has high mechanical strength and is an ideal thermal management material for objects such as buildings. Moreover, its preparation method is simple, easy, safe and reliable, and suitable for large-scale application. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 A flow chart of the preparation process of the selective radiation refrigeration sponge of the present invention.

[0014] Figure 2 Microstructure diagram of the selective infrared emitting sponge prepared in Example 1.

[0015] Figure 3 Solar spectrum reflectivity of the selective infrared emitting sponge prepared in Example 1.

[0016] Figure 4Selective infrared emissivity of the selective infrared emitting sponge prepared in Example 1. DETAILED DESCRIPTION

[0017] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the technical solution of the present invention is further described in detail below through embodiments in conjunction with the accompanying drawings.

[0018] Embodiment 1 The polyoxymethylene is dissolved in a hexafluoroisopropanol solvent, the dissolution temperature is maintained at about 50°C, and the dissolution concentration is 6%-12% by mass. The obtained uniform solution is placed in a low temperature environment of -16°C to -5°C, so that the hexafluoroisopropanol solidifies, and the polyoxymethylene precipitates from the hexafluoroisopropanol to form a solid block. The precipitated block material is soaked in ethanol so that the hexafluoroisopropanol molecules in the block are dissolved in ethanol. After soaking for 2-3 days, the block material is completely transformed into a block composed of polyoxymethylene and ethanol, and the sponge can be obtained by drying in an ordinary oven at 60°C to 80°C for 12 hours.

[0019] like Figure 2 As shown in FIG. 1 , the obtained sponge is composed of particles with a diameter of 1-2 μm, which are interconnected to form a block and have a high porosity. Figure 3 As shown in the figure, the sponge also has a high solar spectrum reflectivity, and its solar spectrum reflectivity is 97% after weighted average. Figure 4 As shown, it has selective infrared emissivity at the atmospheric window (8-13μm). At the same time, it also has the characteristics of low thermal conductivity. When the sponge is placed under the sun for testing, it achieves an efficient cooling effect 5-10℃ below room temperature, which is the result of its multifunctional coupling.

[0020] Embodiment 2 Polyethylene oxide is dissolved in deionized water, the dissolution temperature is maintained at about 70°C, and the dissolution concentration is 6%-8% by mass. The obtained uniform solution is placed in a low temperature environment of -16°C to -5°C, so that the water solidifies and polyethylene oxide precipitates from the water to form a solid block. The precipitated block material is soaked in N,N-dimethylacetamide (DMF) at the solidification point, so that the water molecules in the block are dissolved in DMF. After soaking for 2-3 days, the block material is completely transformed into a block composed of polyethylene oxide and DMF, and the sponge can be obtained by drying in an ordinary oven at 80°C to 100°C for 20-24 hours. The obtained sponge is composed of micron-sized particles, which are interconnected to form a block and have a high porosity. The sponge also has the characteristics of high solar spectrum reflectivity, selective infrared emissivity, and low thermal conductivity. When the sponge is placed under the sun for testing, it achieves an efficient cooling effect of 5-10°C below room temperature, which is precisely the result of its multifunctional coupling.

[0021] The embodiments described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above are only some embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for preparing a selective radiation cooling sponge, characterized in that: The following steps are involved: 1) dissolving the selective infrared emitting polymer in a benign solvent to form a uniform solution; 2) placing the uniform solution obtained in step 1) in a low temperature environment so that the benign solvent is converted into a solid state, and then the polymer is precipitated from the solvent to form a block composed of polymer-solid solvent; 3) The block formed in step 2) is directly immersed in a poor solvent in a low temperature environment, so that the good solvent molecules in the block are dissolved in the poor solvent, and then completely transformed into a gel block composed of a polymer and a poor solvent, and then dried to obtain a selective radiation cooling sponge.

2. The preparation method according to claim 1, characterized in that The selective infrared emitting polymer in step 1) is polyoxymethylene or polyethylene oxide, the dissolution temperature is maintained in the range of 45° C.-80° C., and the dissolution concentration is 6%-12% by mass.

3. The preparation method according to claim 2, characterized in that: In step 1), the selective infrared emitting polymer is polyoxymethylene, and its benign solvent is hexafluoroisopropanol; or, the selective infrared emitting polymer is polyethylene oxide, and its benign solvent is deionized water or ethanol.

4. The preparation method according to claim 1, characterized in that: The low temperature environment in step 2) refers to a low temperature environment of -16°C to -5°C, which is lower than the solidification temperature of benign solvents.

5. The preparation method according to claim 1, characterized in that: Step 3) Soak the block directly in a poor solvent with a freezing point below -16°C for 2-3 days.

6. The preparation method according to claim 1, characterized in that: The poor solvent in step 3) is selected from one or more of ethanol, tetrahydrofuran, and N,N-dimethylformamide.

7. The preparation method according to claim 1, characterized in that: The drying in step 3) is carried out in an oven at 60°C-100°C under normal pressure.

8. The selective radiation cooling sponge obtained by the preparation method according to any one of claims 1 to 7.

9. The selective radiation cooling sponge according to claim 8, characterized in that: The selective radiation cooling sponge has a selective infrared emissivity at an atmospheric window of 8-13 μm.

10. Use of the selective radiation cooling sponge according to claim 8 as a thermal management material.

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