A selective radiative refrigeration sponge for efficient refrigeration and a method of making the same

Abstract

The application discloses a selective radiation refrigeration sponge for efficient refrigeration and a preparation method thereof, and belongs to the field of thermal management materials. The selective radiation refrigeration sponge is prepared by a low-temperature precipitation method and a solvent exchange method, the obtained sponge is composed of micrometer-level particles, the particles are connected with each other to form a block, and the sponge has high porosity. The sponge has the characteristics of high solar spectrum reflectivity, selective infrared emissivity and low thermal conductivity, and can realize efficient refrigeration. In addition, due to the mutual adhesion characteristics of the internal particles, the sponge has high mechanical strength, and is an ideal thermal management material suitable for buildings and the like. The preparation method is simple and easy to implement, safe and reliable, and is suitable for large-scale application.

Description

Technical Field

[0001] This invention relates to the field of building thermal management, specifically to a thermal management material for high-efficiency cooling and its preparation method. The high-efficiency cooling effect stems from the infrared radiation selectivity and low thermal conductivity of the sponge. Background Technology

[0002] Buildings exposed to sunlight absorb significant amounts of solar radiation and ambient infrared radiation, causing active thermal management technologies to consume substantial amounts of energy and resulting in significant greenhouse gas emissions. Establishing passive thermal management technologies can effectively alleviate this situation. Radiative cooling technology has gained widespread attention in recent years. It passively reduces the temperature of buildings and other outdoor objects by reflecting almost all sunlight and enhancing infrared emission (8-13 μm) through atmospheric windows, thereby reducing energy consumption for thermal management. From the basic heat dissipation equation:

[0003] P Cool (T)=P Rad (T)-P Atm (T Amb )-P Sun -P Cond+Conv (T)

[0004] Where P Cool (T) represents the radiative cooling power density, P Rad (T) represents the infrared radiation power density of the object, P Atm (T Amb P represents the atmospheric infrared radiation power density. Sun P is the absorbed solar radiation power density. Cond+Conv (T) represents the power density of heat entering the object from the air through thermal conduction and convection, and T represents the temperature of the object. Amb Room temperature.

[0005] When a radiation-cooling material has selective infrared emissivity and low thermal conductivity (i.e., it has high infrared emissivity only at atmospheric windows, and reduces atmospheric infrared radiation in non-atmospheric window regions due to low infrared emissivity (i.e., P...), it is suitable for applications where the material exhibits high infrared emissivity only at atmospheric windows and low infrared emissivity at non-atmospheric window regions. Atm (T Amb (The absorption of heat and low thermal conductivity can reduce the intrusion of ambient heat into the material through convection and conduction, thus further improving the cooling performance.)

[0006] Existing literature reports selective radiative cooling materials, such as polyoxymethylene (POM), polyethylene oxide (PEO), and silicon dioxide, which exhibit selective infrared emission due to their well-symmetrical molecular structures and fewer infrared resonance modes. To meet the requirement of high solar spectral reflectivity, these materials are typically prepared using electrospinning or coating methods. For example, patent publication CN116790087A discloses a selective infrared emitting material based on POM and PTFE, prepared via electrospinning, and used to improve cooling performance. Similarly, patent publication CN113513858A discloses a selective infrared emitting ceramic coating for enhancing cooling efficiency. Objectively speaking, while these materials can satisfy the requirements of high solar spectral reflectivity and selective infrared emission in radiative cooling, they cannot simultaneously achieve low thermal conductivity. Summary of the Invention

[0007] The purpose of this invention is to provide a radiative cooling material with high solar spectral reflectivity, selective infrared emission, and low thermal conductivity, which can effectively achieve passive cooling and further improve the cooling effect, enabling building surfaces to achieve a lower temperature state, thereby reducing the use of indoor active thermal management equipment.

[0008] To achieve the above objectives, this invention provides a method for preparing selectively radiative sponges using a low-temperature precipitation method and a solvent exchange method. This method constructs a sponge with improved functional integrity and cooling performance, possessing selective infrared emissivity, high solar spectral reflectivity, and low thermal conductivity, suitable for efficient building cooling. The sponge exhibits selective infrared emissivity and low thermal conductivity; that is, it has high infrared emissivity only at atmospheric windows, while the low infrared emissivity in non-atmospheric window areas reduces the absorption of ambient infrared radiation. The low thermal conductivity also reduces the intrusion of ambient heat into the material through convection and conduction, thereby achieving efficient cooling.

[0009] Specifically, this invention proposes a selective radiation cooling sponge for high-efficiency refrigeration applications, the preparation method of which includes:

[0010] 1) Dissolve the selective infrared emitting polymer in a benign solvent to form a homogeneous solution;

[0011] 2) Place the homogeneous solution obtained in step 1) in a low-temperature environment to allow the good solvent to transform into a solid state, thereby causing the polymer to precipitate from the solvent and form a block composed of polymer and solid solvent;

[0012] 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 dissolve in the poor solvent, thereby completely transforming it into a gel block composed of polymer and poor solvent. Then it is dried to obtain a selective radiation cooling sponge.

[0013] The above-mentioned selective radiation cooling sponge preparation process includes low-temperature precipitation method and solvent exchange method. Figure 1 The terms "good solvent" and "bad solvent" refer to selective infrared-emitting polymers. The selective infrared-emitting polymers mentioned in step 1), such as polyoxymethylene (POM) and polyethylene oxide (PEO), are dissolved in a good solvent at a temperature maintained between 45°C and 80°C, with a concentration of 6% to 12% by mass. For POM, a good solvent is, for example, hexafluoroisopropanol; for PEO, a good solvent is, for example, deionized water or ethanol.

[0014] In step 2) above, preferably, the obtained homogeneous solution is placed in a low-temperature environment of -16°C to -5°C, so that the good solvent is converted into a solid, thereby causing the polymer to precipitate from the solvent and form a block composed of polymer and solid solvent.

[0015] In step 3) above, preferably, the block is immersed in a poor solvent with a freezing point below -16°C, so that the good solvent molecules in the block dissolve 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 at normal pressure in an oven at 60°C-100°C. The poor solvent has a freezing point below -16°C, such as ethanol, tetrahydrofuran, N,N-dimethylformamide (DMF), etc.

[0016] The sponge obtained by this invention is composed of micron-sized particles that are interconnected to form a bulk mass and have high porosity. The microstructure of the sponge creates strong Mie scattering, resulting in high solar spectral reflectivity; the strong symmetry of its molecular structure creates selective infrared emissivity, exhibiting high infrared emissivity in the atmospheric window (8-13 μm); and the porous structure of the sponge results in low thermal conductivity.

[0017] The selective radiation cooling sponge prepared by this invention through low-temperature precipitation and solvent exchange methods possesses high solar spectral reflectivity, selective infrared emissivity, and low thermal conductivity, enabling efficient cooling. Furthermore, due to the inter-particle adhesion, it exhibits high mechanical strength, making it an ideal thermal management material for buildings and other applications. Moreover, its preparation method is simple, safe, and reliable, suitable for large-scale applications. Attached Figure Description

[0018] Figure 1 The process flow diagram for preparing the selective radiation cooling sponge of this invention.

[0019] Figure 2 Microstructure diagram of the selective infrared emitting sponge prepared in Example 1.

[0020] Figure 3Solar spectral reflectance of the selective infrared emitting sponge prepared in Example 1.

[0021] Figure 4 Selective infrared emissivity of the selective infrared emitting sponge prepared in Example 1. Detailed Implementation

[0022] To make the objectives, technical solutions, and advantages of the present invention clearer, the technical solutions of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments.

[0023] Example 1

[0024] Polyoxymethylene (POM) is dissolved in hexafluoroisopropanol (HEP) solvent at a temperature maintained at approximately 50°C, achieving a concentration of 6%-12% by mass. The resulting homogeneous solution is placed in a low-temperature environment of -16°C to -5°C, causing the HEP to solidify and POM to precipitate out, forming a solid mass. The precipitated mass is then immersed in ethanol, dissolving the HEP molecules within the mass. After immersion for 2-3 days, the mass is completely transformed into a mass composed of POM and ethanol. This mass is then dried in a standard oven at 60°C to 80°C for 12 hours to obtain the sponge.

[0025] like Figure 2 As shown, the obtained sponge consists of particles with a diameter of 1-2 micrometers, which are interconnected to form a mass and have a high porosity. Figure 3 As shown, the sponge also has high solar spectral reflectance, with a weighted average solar spectral reflectance of 97%. Figure 4 As shown, it exhibits selective infrared emissivity at the atmospheric window (8-13 μm). It also possesses low thermal conductivity. When tested under sunlight, the sponge achieved a highly efficient cooling effect 5-10°C below room temperature, which is a result of its multifunctional coupling.

[0026] Example 2

[0027] Polyethylene oxide (PE) is dissolved in deionized water at a temperature maintained at approximately 70°C, resulting in a concentration of 6%-8% by mass. The resulting homogeneous solution is placed in a low-temperature environment of -16°C to -5°C, causing the water to freeze and PE to precipitate, forming a solid mass. This precipitated mass is then immersed in N,N-dimethylacetamide (DMF), which has a freezing point of approximately 50°C, allowing water molecules within the mass to dissolve. After 2-3 days of immersion, the mass is completely transformed into a mass composed of PE and DMF. This mass is then dried in a conventional oven at 80°C to 100°C for 20-24 hours to obtain a sponge. The resulting sponge consists of micron-sized particles interconnected to form a mass with high porosity. The sponge also exhibits high solar spectral reflectivity, selective infrared emissivity, and low thermal conductivity. When tested under sunlight, the sponge achieves a highly efficient cooling effect 5-10°C below room temperature, a result of its multifunctional coupling.

[0028] The embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above descriptions 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 within the protection scope of the present invention.

Claims

1. A method for preparing a selectively radiatively cooled sponge, characterized in that, Includes the following steps: 1) Dissolve the selective infrared emitting polymer in a good solvent to form a homogeneous solution, wherein the selective infrared emitting polymer is polyoxymethylene or polyethylene oxide, the dissolution temperature is maintained in the range of 45℃-80℃, and the dissolution concentration is 6%-12% by mass. 2) Place the homogeneous solution obtained in step 1) in a low-temperature environment of -16°C to -5°C to allow the good solvent to transform into a solid state, thereby causing the polymer to precipitate from the solvent and form a block composed of polymer and solid solvent. 3) The block formed in step 2) is directly immersed in a poor solvent with a freezing point below -16°C in a low-temperature environment, so that the good solvent molecules in the block dissolve in the poor solvent, thereby completely transforming it into a gel block composed of polymer and poor solvent. Then it is dried to obtain a selective radiation cooling sponge.

2. The preparation method according to claim 1, 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.

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

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

5. The preparation method according to claim 1, characterized in that, The drying described in step 3) is performed in an oven at 60℃-100℃ under normal pressure.

6. The selective radiation-cooling sponge obtained by the preparation method according to any one of claims 1-5.

7. The selective radiation cooling sponge as described in claim 6, characterized in that, The selective radiation cooling sponge has selective infrared emissivity at an atmospheric window of 8-13 μm.

8. The application of the selective radiation cooling sponge as described in claim 6 or 7 as a thermal management material.

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