Cooling structure and method for producing cooling structure

Abstract

This cooling structure comprises: an object to be cooled which is placed under a solar radiation environment; and a film which is formed on the surface of the object to be cooled and contains ceramic particles. The ceramic particles have an average emissivity of 80% or more in the wavelength band of 8-13 μm, and an average reflectivity of 80% or more in the wavelength band of 1 μm or less.

Description

Cooling structure and method for manufacturing the cooling structure

[0001] This application claims priority to Japanese Patent Application No. 2023-138530, filed with the Japan Patent Office on August 29, 2023, the contents of which are incorporated herein by reference.

[0002] For example, in facilities that house a variety of equipment, such as data centers, logistics warehouses, and factories, it is necessary to control the internal temperature within an appropriate range in order for the equipment to function properly. Conventionally, air conditioning equipment has often been used to control the temperature inside such facilities, but from the perspective of energy conservation and reducing environmental impact, new methods to replace air conditioning equipment are required.

[0003] As one of the means, a technology has been developed in recent years in which a radiative cooling material is applied to the exterior wall of a building housing the equipment, thereby releasing the heat accumulated on the exterior wall due to sunlight to the outside and improving the cooling performance. For example, Patent Document 1 proposes, as an example of this type of radiative cooling material, that a multilayer coating made of a combination of multiple resin materials is applied to the surface of the object to be cooled, thereby achieving good cooling performance in a sunshine environment through solar reflection and radiative cooling performance.

[0004] Japanese Patent Application Laid-Open No. 2021-143796

[0005] In the above-mentioned Patent Document 1, a multilayer coating composed of a combination of multiple resin materials is used as a radiative cooling material. Because such a multilayer coating contains resin materials, its performance is likely to deteriorate or the coating is likely to peel off due to environmental degradation caused by ultraviolet rays contained in sunlight. Furthermore, when the object to be cooled has a complex shape, a structure formed in a sheet form such as a multilayer coating is difficult to apply and tends to be costly.

[0006] At least one embodiment of the present disclosure has been made in consideration of the above-mentioned circumstances, and aims to provide a cooling structure that has excellent weather resistance and can be realized by easy coating application, and a method for manufacturing a cooling structure.

[0007] In order to solve the above problems, a cooling structure according to at least one embodiment of the present disclosure comprises: an object to be cooled that is placed in a solar radiation environment; and a coating formed on the surface of the object to be cooled and containing ceramic particles, wherein the ceramic particles have an average emissivity of 80% or more in a wavelength band of 8-13 μm and an average reflectance of 80% or more in a wavelength band of 1 μm or less.

[0008] In order to solve the above problems, a method for manufacturing a cooling structure according to at least one embodiment of the present disclosure includes a step of forming a coating containing ceramic particles on a surface of an object to be cooled that is placed in a solar radiation environment, and the ceramic particles have an average emissivity of 80% or more in the 8-13 μm wavelength band and an average reflectance of 80% or more in the wavelength band of 1 μm or less.

[0009] According to at least one embodiment of the present disclosure, it is possible to provide a cooling structure that has excellent weather resistance and can be realized by easy coating application, and a method for manufacturing the cooling structure.

[0010] 5 is a schematic configuration diagram showing a cooling structure according to an embodiment from the side; FIG. 5 is an example of measurement results of the reflection characteristics of a thermal sprayed coating of yttria-stabilized zirconia contained in the coating of FIG. 1; FIG. 5 is an example of measurement results of the radiation characteristics of a thermal sprayed coating of yttria-stabilized zirconia contained in the coating of FIG. 1; FIG. 5 is a schematic diagram showing a verification test using a test specimen simulating the cooling structure of FIG. 1; FIG. 5 is an enlarged view of the vicinity of 14:00 in FIG. 5;

[0011] Hereinafter, several embodiments will be described with reference to the accompanying drawings. However, the dimensions, materials, shapes, relative arrangements, etc. of the components described as embodiments or shown in the drawings are merely illustrative examples and are not intended to limit the scope of the invention.

[0012] 1 is a schematic side view of a cooling structure 10 according to one embodiment. The cooling structure 10 includes an object to be cooled 12 that is placed in a solar radiation environment, and a coating 14 formed on the surface of the object to be cooled 12.

[0013] The object to be cooled 12 is, for example, the outer wall of a building that includes equipment in a sunlit environment. In this embodiment, an outer wall facing upward is illustrated as the object to be cooled 12, but the object to be cooled 12 may face the other direction. The shape of the object to be cooled 12 shown in FIG. 1 is merely an example, and the object to be cooled 12 may have a more complex shape, such as an uneven surface.

[0014] The coating 14 is provided so as to cover at least a portion of the surface of the object to be cooled 12. The coating 14 may be provided so as to cover the entire surface of the object to be cooled 12, or may be provided only on a portion of the surface.

[0015] The coating 14 includes ceramic particles. The ceramic particles included in the coating 14 have an average emissivity of 80% or more in the 8-13 μm wavelength band and an average reflectance of 80% or more in the 1 μm or shorter wavelength band. Specifically, the ceramic particles include a zirconia-based material, and more preferably, the zirconia-based material is yttria-stabilized zirconia.

[0016] 2 and 3, the characteristics of a thermally sprayed coating of yttria-stabilized zirconia, which is an example of ceramic particles contained in coating 14, will be described. Fig. 2 shows an example of the measurement results of the reflection characteristics of a thermally sprayed coating of yttria-stabilized zirconia contained in coating 14 of Fig. 1, and Fig. 3 shows an example of the measurement results of the radiation characteristics of a thermally sprayed coating of yttria-stabilized zirconia contained in coating 14 of Fig. 1.

[0017] 2 shows the reflectance characteristics versus wavelength for each thickness of the coating 14 containing yttria-stabilized zirconia. As shown in FIG. 2, the coating 14 containing yttria-stabilized zirconia exhibits high reflectance in the wavelength range of 0.3 to 3 μm (see the hatched area in FIG. 2) at all thicknesses. The reflectance also increases as the thickness of the coating 14 increases. This wavelength range corresponds to the wavelength range of the solar spectrum, and therefore the coating 14 effectively reflects solar light, thereby preventing the object 12 to be cooled covered with the coating 14 from heating up.

[0018] Figure 3 shows the emissivity characteristics versus wavelength for each thickness of the coating 14 containing yttria-stabilized zirconia. As shown in Figure 3, the coating 14 containing yttria-stabilized zirconia exhibits high emissivity in the wavelength range of 8 to 14 μm (see the hatched area in Figure 3) at all thicknesses. The emissivity is shown to increase as the thickness of the coating 14 decreases. This wavelength range corresponds to a wavelength range that is not absorbed by the atmosphere, and therefore is less likely to be absorbed by the atmosphere, which indicates that the object 12 covered by the coating 14 is more likely to be cooled by the radiative cooling effect.

[0019] The wavelength range of 8 to 14 μm, which is not absorbed by the atmosphere, is known as the "atmospheric window." In this wavelength range, a large amount of heat can be dissipated into space due to the large temperature difference between this range and outer space, which is approximately -270°C.

[0020] Thus, by selecting an appropriate film thickness, yttria-stabilized zirconia can achieve both ideal reflective and radiative properties as a coolant. Therefore, by using yttria-stabilized zirconia as the ceramic particles contained in the coating 14, good cooling action can be achieved even in a single-layer configuration that is easy to apply. Specifically, in the case of a thermal spray coating, a film thickness of approximately 0.3 to 0.5 mm is desirable in order to achieve an average reflectance of 80% or more in the wavelength band of 1 μm or less and an average emissivity of 80% or more in the wavelength band of 8 to 13 μm.

[0021] Next, the results of a verification test conducted on the cooling performance of the cooling structure 10 having the above configuration will be described. Fig. 4 is a schematic diagram showing the verification test using a test body 20 simulating the cooling structure of Fig. 1, Fig. 5 shows the temperature measurement results of each sample of the test body 20, and Fig. 6 is an enlarged view of Fig. 5 around 14:00. In addition to each sample, Figs. 5 and 6 also show, as reference data, the measurement results of a plain wood with nothing applied to the surface of the metal box 28, a black paint-applied material, and the outside air temperature.

[0022] This verification test used a test specimen 20 having a configuration equivalent to the cooling structure 10 described above. As shown in FIG. 4 , the test specimen 20 is constructed by laying, from bottom to top, urethane foam 24 and glass wool 26 inside a hollow acrylic box 22 with an open top. A metal box 28 made of, for example, SUS is placed on the glass wool 26 as a simulated cooling object 12, and Samples 1 to 6 corresponding to the coating 14 are provided on the top surface of the metal box 28. The glass wool 26 is a heat insulating member for eliminating thermal effects from the side of the acrylic box 22 on the metal box 28. Samples 1 to 6, along with the top surface of the acrylic box 22, are covered with a polyethylene film 30 to eliminate the effects of convection.

[0023] Samples 1 to 3 were applied by thermal spraying and have different thicknesses t = 0.1, 0.3, and 0.5 mm. Sample 4 was applied by the sol-gel method and formed by spraying, drying, and baking. Sample 5 was applied by the sol-gel method and formed by spraying and drying (no baking). Sample 6 was applied by the sol-gel method and formed by brushing and drying.

[0024] As shown in Figures 5 and 6, Samples 1 to 6 all have lower surface temperatures than black bodies and solid wood, providing good cooling effects. Comparing the test results for Samples 1 to 13, it is clear that for coatings 14 applied by thermal spraying, the greater the film thickness t, the better the cooling effect. Furthermore, Samples 4 to 6 have lower temperatures than Samples 1 to 3, indicating that coatings 14 applied by the sol-gel method have better cooling effects than those applied by thermal spraying. Furthermore, Sample 6 has the lowest temperature of Samples 4 to 6, indicating that the sample that was brushed and then dried provides the best cooling effect.

[0025] As described above, according to each of the above embodiments, a coating 14 containing ceramic particles is formed on the surface of the object to be cooled 12. The ceramic particles contained in the coating 14 have excellent emissivity in the 8-13 μm wavelength band, which is highly transparent to the atmosphere (a wavelength band not absorbed by the atmosphere, corresponding to the so-called "atmospheric window"), and also have excellent reflectivity in the wavelength band of 1 μm or less, which can effectively reflect the solar spectrum. By using a coating containing ceramic particles having excellent reflectivity and emissivity in each wavelength band, it is possible to effectively cool the object to be cooled 12.

[0026] In addition, within the scope of the present disclosure, the components in the above-described embodiments may be replaced with well-known components as appropriate, and the above-described embodiments may be combined as appropriate.

[0027] The contents described in each of the above embodiments can be understood, for example, as follows.

[0028] (1) A cooling structure according to one embodiment comprises: an object to be cooled that is placed in a solar radiation environment; and a coating formed on the surface of the object to be cooled and containing ceramic particles, wherein the ceramic particles have an average emissivity of 80% or more in a wavelength band of 8-13 μm and an average reflectance of 80% or more in a wavelength band of 1 μm or less.

[0029] According to the above configuration (1), a coating containing ceramic particles is formed on the surface of an object to be cooled. The ceramic particles contained in the coating have excellent emissivity in the 8-13 μm wavelength band, which is highly transparent to the atmosphere (a wavelength band not absorbed by the atmosphere, corresponding to the so-called "atmospheric window"), and also have excellent reflectivity in the wavelength band of 1 μm or less, which can effectively reflect the solar spectrum. By using a coating containing ceramic particles having excellent reflectivity and emissivity in each wavelength band, it is possible to effectively cool the object to be cooled.

[0030] (2) In another aspect, in the above aspect (1), the ceramic particles include a zirconia-based material.

[0031] According to the above aspect (2), by using a zirconia-based material as the ceramic particles contained in the coating, it is possible to achieve excellent reflectance and emissivity for each of the above wavelength bands.

[0032] (3) In another aspect, in the above aspect (2), the zirconia-based material includes yttria-stabilized zirconia.

[0033] According to the above aspect (3), for example, yttria-stabilized zirconia can be used as ceramic particles having excellent reflectance and emissivity in each of the wavelength bands.

[0034] (4) In another aspect, in any one of the above aspects (1) to (3), the object to be cooled is an exterior wall of a building.

[0035] According to the above aspect (4), by applying the coating having the above configuration to the exterior wall of a building that is exposed to sunlight as the object to be cooled, a good cooling effect can be obtained.

[0036] (5) A method for manufacturing a cooling structure according to one embodiment includes a step of forming a coating containing ceramic particles on a surface of an object to be cooled that is placed in a solar radiation environment, and the ceramic particles have an average emissivity of 80% or more in a wavelength band of 8-13 μm and an average reflectance of 80% or more in a wavelength band of 1 μm or less.

[0037] According to the above aspect (5), a coating containing ceramic particles is formed on the surface of an object to be cooled. The ceramic particles contained in the coating have excellent emissivity in the 8-13 μm wavelength band, which is highly transparent to the atmosphere (a wavelength band not absorbed by the atmosphere, corresponding to the so-called "atmospheric window"), and also have excellent reflectivity in a wavelength band of 1 μm or less, which can effectively reflect the solar spectrum. By using a coating containing ceramic particles having excellent reflectivity and emissivity in each wavelength band, it is possible to effectively cool the object to be cooled.

[0038] (6) In another aspect, in the above aspect (5), the coating is formed by a sol-gel method.

[0039] According to the above aspect (6), a coating containing ceramic particles is applied to the surface of the object to be cooled by a sol-gel method, thereby exhibiting an excellent cooling effect.

[0040] (7) In another aspect, in the aspect (5), the coating is formed by a thermal spraying method.

[0041] According to the above aspect (7), a coating containing ceramic particles is applied to the surface of the object to be cooled by a thermal spraying method, which results in a coating with superior adhesion and durability, although the cooling effect is inferior to that of the sol-gel method.

[0042] (8) In another aspect, in the above aspect (5), the coating is formed by a coating method or a spray method.

[0043] According to the above aspect (8), the coating containing ceramic particles is applied to the surface of the object to be cooled by a coating method or a spraying method, which requires simple equipment and allows the coating to be flexibly applied to the surface of objects to be cooled having various shapes.

[0044] REFERENCE SIGNS LIST 10 Cooling structure 12 Cooling object 14 Film 20 Test specimen 22 Acrylic box 24 Urethane foam 26 Glass wool 28 Metal box 30 Polyethylene film

Claims

1. A cooling structure comprising: an object to be cooled that is placed in a solar radiation environment; and a coating formed on the surface of the object to be cooled that contains ceramic particles, wherein the ceramic particles have an average emissivity of 80% or more in the 8-13 μm wavelength band and an average reflectance of 80% or more in the 1 μm or shorter wavelength band.

2. The cooling structure of claim 1, wherein the ceramic particles comprise a zirconia-based material.

3. The cooling structure of claim 2, wherein the zirconia-based material comprises yttria-stabilized zirconia.

4. A cooling structure according to any one of claims 1 to 3, wherein the object to be cooled is an exterior wall of a building.

5. A method for manufacturing a cooling structure, comprising a step of forming a coating containing ceramic particles on the surface of an object to be cooled that is placed in a solar radiation environment, wherein the ceramic particles have an average emissivity of 80% or more in the 8-13 μm wavelength band and an average reflectance of 80% or more in the 1 μm or less wavelength band.

6. The method for manufacturing a cooling structure according to claim 5, wherein the coating is formed by a sol-gel method.

7. The method for manufacturing a cooling structure according to claim 5, wherein the coating is formed by a thermal spraying method.

8. The method for manufacturing a cooling structure according to claim 5, wherein the coating is formed by a coating method or a spray method.

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