Radiation cooling device

Abstract

To provide a radiation cooling device that is improved in durability.SOLUTION: A sheet-like radiation cooling device is fitted to a substrate. A number of through-holes are formed in the sheet-like radiation cooling device. Each of the through-holes is preferably formed in the apex of a projection that projects on an opposite side of a surface opposite to the substrate.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a radiative cooling device. [Background technology]

[0002] Efforts aimed at mitigating or reducing the impact of climate change have been ongoing for some time, and research and development into reducing carbon dioxide emissions has been conducted to achieve this. One example of such an effort is a technology disclosed in which a sheet-like radiative cooling device with a cooling effect is attached to the surface of an object to be cooled, thereby cooling the object without consuming energy such as electricity (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 6821063 Summary of the Invention [Problem to be solved by the invention]

[0004] In the above technology, when the radiative cooling device and the substrate to be cooled are placed outdoors, water may penetrate between the substrate and the radiative cooling device depending on the conditions, such as harsh environments or insufficient sealing measures. When water penetrates, depending on the components contained in the water, corrosion may occur, generating gas between the substrate and the radiative cooling device, causing swelling in the cooling radiative cooling device and reducing the durability of the radiative cooling device.

[0005] The present invention has been made in consideration of the above, and aims to provide a radiative cooling device with improved durability. [Means for solving the problem]

[0006] (1) The present invention relates to a sheet-like radiative cooling device attached to a substrate, the sheet-like radiative cooling device having a large number of through-holes formed therein.

[0007] According to the invention (1), a radiative cooling device with improved durability can be provided.

[0008] (2) The radiative cooling device according to (1), wherein the through-hole is formed at the top of a protrusion that protrudes on the side opposite to the surface facing the substrate.

[0009] According to the invention (2), it is possible to make it difficult for water droplets to enter between the radiative cooling device and the base material from the outside through the through holes.

[0010] (3) The radiative cooling device according to (1) or (2), wherein the substrate is a zinc-treated substrate.

[0011] According to the invention of (3), even if a radiative cooling device is attached to a zinc-treated substrate, even if gas components are generated between the radiative cooling device and the substrate, the gas can be preferably released to the outside.

[0012] (4) The through-hole has a hole area of ​​15,600 μm 2 The radiative cooling device according to any one of (1) to (3) above.

[0013] According to the invention (4), even if a gas component is generated between the radiative cooling device and the substrate, the gas can be preferably released to the outside.

[0014] (5) The radiative cooling device according to any one of (1) to (4), wherein the through-holes have an area ratio of 0.12% to 0.28%.

[0015] According to the invention of (5), even if gas components are generated between the radiative cooling device and the substrate, the gas can be preferably released to the outside, and the radiative cooling effect of the radiative cooling device can be maintained.

[0016] (6) The radiative cooling device according to any one of (1) to (5), wherein the distance between the through holes is 5 mm to 8 mm.

[0017] According to the invention of (6), even if gas components are generated between the radiative cooling device and the substrate, the gas can be preferably released to the outside, and the radiative cooling effect of the radiative cooling device can be maintained.

[0018] (7) The radiative cooling device according to any one of (1) to (6), wherein the protrusions have a protrusion height of 100 μm or more.

[0019] According to the invention (7), it is possible to obtain an effect that water droplets such as rainwater are less likely to enter from the outside through the through holes. [Brief explanation of the drawings]

[0020] [Figure 1] FIG. 1 is a perspective view schematically illustrating a radiative cooling device according to an embodiment. [Figure 2] FIG. 1 is a cross-sectional view schematically illustrating a radiative cooling device according to an embodiment. [Figure 3A] 1 shows the results of a simulation in which water droplets are dropped onto the surface of a radiative cooling device according to one embodiment. [Figure 3B] 1 shows the results of a simulation in which water droplets are dropped onto the surface of a radiative cooling device according to one embodiment. [Figure 4A] FIG. 1 shows an overview of the test rig for estimating the preferred hole area of ​​a radiative cooling device. [Figure 4B] 1 is a graph showing the relationship between the hole area of ​​a radiative cooling device and the residual pressure inside the device. [Figure 5] 1 is a graph showing the relationship between heating time and swollen area ratio in an accelerated heating test. [Figure 6] 10 is a graph showing the relationship between the pitch of through holes and the bulge area ratio. [Figure 7] 10 is a graph showing the relationship between the hole area ratio of through holes and the bulge area ratio. DETAILED DESCRIPTION OF THE INVENTION

[0021] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0022] <Radiation cooling device> The radiative cooling device 1 is a sheet-like device with radiative cooling properties. Radiative cooling refers to the action of a substance lowering its temperature by radiating electromagnetic waves such as infrared rays to the surroundings. The radiative cooling device 1 is attached to the surface of the substrate B to be cooled. Examples of the attachment method include attaching the device to the substrate surface with an adhesive or an adhesive layer formed in advance on the radiative cooling device 1. For example, the radiative cooling device 1 may include an infrared radiating layer that radiates infrared light from the radiating surface and a light reflective layer that is placed on the side opposite to the radiating surface.

[0023] The infrared radiation layer is a layer disposed on the incident side of light such as sunlight, and reflects a portion of the incident light from the radiation surface and transmits a portion of the light. The infrared radiation layer also converts heat transferred to the substrate B (the cooling target) (e.g., heat transferred from the atmosphere) into infrared light and radiates it to the outside. Such an infrared radiation layer is made of a resin material. By adjusting the thickness of the resin material, it is possible to emit a large amount of thermal radiation in the so-called atmospheric window wavelength band (a wavelength band from 8 μm to 14 μm). Specifically, it is preferable to configure the infrared radiation layer so that the light absorptance of sunlight is 10% or less, the energy is 100 W or less, and the wavelength average emissivity from 8 μm to 14 μm is 40% or more. Such an infrared radiation layer can be obtained, for example, by configuring it from vinyl chloride resin or vinylidene chloride resin and setting the thickness to 10 μm to 100 μm.

[0024] The light-reflecting layer is a layer that reflects light such as sunlight that has passed through the infrared radiation layer. The light-reflecting layer preferably has a reflectance of 90% or more for light with a wavelength between 400 nm and 500 nm, and a reflectance of 96% or more for light with a wavelength longer than 500 nm. Examples of such a light-reflecting layer include those essentially composed of silver or a silver alloy. The light-reflecting layer may also contain aluminum or an aluminum alloy. When the light-reflecting layer is composed only of silver or a silver alloy, the thickness is preferably 50 nm or more and 100 μm or less. When the light-reflecting layer has a laminated structure in which silver or a silver alloy is laminated with aluminum or an aluminum alloy, the thickness of the silver is preferably 10 nm or more and the thickness of the aluminum is preferably 30 nm or more.

[0025] Each layer constituting the radiative cooling device 1 is flexible, and therefore the radiative cooling device 1 itself is also flexible. The configuration of the radiative cooling device 1 is not limited to the above, and the radiative cooling device 1 may have other layers as long as they do not impede the radiative cooling effect. For example, a protective layer may be provided between the infrared emitting layer and the light reflecting layer. Furthermore, an adhesive layer may be provided on the surface of the light reflecting layer opposite the infrared emitting layer, that is, the surface that abuts against the substrate B.

[0026] (Through hole) As shown in Figure 1, the radiative cooling device 1 has many through-holes 2. When the radiative cooling device 1 is attached to a substrate B and installed outdoors, rainwater may enter between the radiative cooling device 1 and the substrate B from the edge. Because the radiative cooling device 1 is a sheet-like material with high barrier properties, rainwater that enters between the radiative cooling device 1 and the substrate B tends to be difficult to discharge to the outside. If the rainwater corrodes the substrate B and gas is generated, the radiative cooling device 1 will bulge. This will cause the radiative cooling device 1 to peel off from the substrate B. By forming many through-holes 2 in the radiative cooling device 1, rainwater that has entered between the radiative cooling device 1 and the substrate B and the generated gas can be discharged to the outside, suppressing the bulging and improving the durability of the radiative cooling device 1.

[0027] Figure 2 is a schematic diagram showing a cross section of a radiative cooling device 1 arranged so that its surface direction is along the vertical direction. As shown in Figure 2, the radiative cooling device 1 has a protruding portion 10 that protrudes on the side opposite to the surface facing the substrate B. The protruding portion 10 consists of an inclined portion 11 and an apex 12. The through-hole 2 is formed in the apex 12. The inclined portion 11 is a curved surface that continues from a portion of the radiative cooling device 1 where the protruding portion 10 is not formed to the apex 12. The apex 12 is continuous with the inclined portion 11 and is a substantially flat surface that is substantially parallel to the surface of the portion of the radiative cooling device 1 where the protruding portion 10 is not formed. By providing the through-hole 2 in the apex 12, water droplets W are less likely to enter between the radiative cooling device 1 and the substrate B from the outside through the through-hole 2.

[0028] One example of a method for forming the above-described through-hole 2 in the radiative cooling device 1 is to form the through-hole 2 by penetrating a needle member through the radiative cooling device 1. In this case, it is preferable to place a member with a hole on the surface of the radiative cooling device 1 opposite to the penetration side of the needle member, and to form the through-hole 2 by inserting the needle member into the hole. In this way, when the needle member is penetrated through the radiative cooling device 1, a part of the radiative cooling device 1 enters the hole, forming a protrusion 10 consisting of an inclined portion 11 and an apex 12, and forming the through-hole 2 in the apex 12. Furthermore, by adjusting the size of the hole, the height h of the apex 12 can be adjusted.

[0029] The hole area of ​​the through hole 2 is 15,600 μm 2 This is preferable. This allows the gas generated between the radiative cooling device 1 and the base material B to be preferably released to the outside.

[0030] The hole area ratio of the through-holes 2 is preferably 0.12% to 0.28%. In this specification, the hole area ratio means the ratio of the area of ​​the through-holes 2 per unit area of ​​the surface of the radiative cooling device 1. By setting the hole area ratio of the through-holes 2 to the above ratio, gas generated between the radiative cooling device 1 and the base material B can be preferably released to the outside, and the radiative cooling effect of the radiative cooling device 1 can be maintained.

[0031] It is preferable that the large number of through holes 2 are uniformly arranged. In this case, the interval (pitch) between the large number of through holes 2 is preferably 5 mm to 8 mm. 2 In this case, by setting the interval (pitch) between the through holes 2 within the above range, the hole area ratio of the through holes 2 can be set to 0.12% to 0.28%. The uniform arrangement of the through holes 2 is not particularly limited, and they may be arranged in a staggered pattern or a lattice pattern.

[0032] The protrusion height h of the protrusion 10 shown in Figure 2 (the distance between the top 12 and the part of the radiative cooling device 1 where the protrusion 10 is not formed) is preferably 100 μm or more. This makes it difficult for water droplets such as rainwater to enter between the base material B and the radiative cooling device 1 from the outside through the through-holes 2.

[0033] (base material) The substrate B, which is the target to be cooled by the radiative cooling effect of the radiative cooling device 1, is not particularly limited, and may be, for example, a metal plate. When the substrate B is a metal plate, it may generally be zinc-treated for purposes such as rust prevention. If the substrate B is zinc-treated, depending on the conditions, such as when the usage environment is harsh, swelling may occur in the radiative cooling device 1 due to hydrogen gas generated by the sacrificial corrosion protection action of zinc. The radiative cooling device 1 of this embodiment can preferably release hydrogen gas generated between the radiative cooling device 1 and the substrate B to the outside, thereby suppressing the occurrence of swelling. The zinc-treated substrate refers to a substrate coated with a zinc-based anticorrosive paint or a substrate coated with a zinc-based plating (such as non-alloyed hot-dip galvanizing).

[0034] Although the preferred embodiments of the present invention have been described above, the present invention is not limited to the above embodiments and can be modified as appropriate. [Example]

[0035] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the following examples.

[0036] (Water droplet dropping simulation) Figures 3A and 3B show simulation results showing the behavior of water droplets W when the radiative cooling device 1 is placed so that its surface direction is vertical and water droplets W are dropped from above. Figure 3A shows the simulation results when the radiative cooling device 1 has only through-holes 2 without forming protrusions. Figure 3B shows the simulation results when the through-holes 2 are formed at the tops 12 of the protrusions in the above embodiment and the height of the tops is 100 μm. In both cases, the hole area of ​​the through-holes 2 is 15,600 μm 2 The flow analysis software used was "ANSYS Fluent" (manufactured by ANSYS, Inc.) In Figures 3A and 3B, darker areas indicate areas where water droplets exist.

[0037] As shown in Figure 3A, when only through holes 2 are formed without forming protrusions, it is clear that water droplets penetrate from through holes 2 to the substrate side. In contrast, as shown in Figure 3B, when through holes are formed at the apexes 12 of the protrusions and the protrusion height of the protrusions is set to 100 µm, it is clear that water droplets do not penetrate from through holes 2 to the substrate side. As in Figure 3B, a similar simulation was performed when the protrusion height of the protrusions was set to 150 µm and 230 µm, but no penetration of water droplets from through holes 2 to the inner surface side was observed.

[0038] (Decompression evaluation test) A pressure reduction evaluation test was conducted using a chamber C with an internal space and a single hole, as shown in Figure 4A. The specific procedure is as follows: A radiative cooling device 1 with a through-hole 2 was attached to the chamber C so that the hole in the chamber C communicated with the through-hole 2, and then a predetermined pressure P was applied to the inside of the chamber C. Next, the residual pressure in the chamber C was measured after a predetermined time had elapsed. The test was conducted by changing the hole area of ​​the through-hole 2, and the relationship between the hole area and the residual pressure in the chamber was determined. The results are shown in Figure 4B.

[0039] In the graph of FIG. 4B, the horizontal axis represents the hole area (μm 2), and the vertical axis indicates the residual pressure (kPa) in the chamber. The lower the residual pressure in the chamber, the better the gas discharge performance of the through-holes 2. As shown in Figure 4B, there is a certain relationship between the hole area and the residual pressure, and when the hole area is 15,600 μm 2 In this case, the residual pressure in the chamber becomes almost zero, and it is clear that preferable gas discharge properties can be obtained through the through-holes 2.

[0040] (Accelerated swelling test) The accelerated blister test was carried out in the following manner. First, the hole area of ​​the through-hole 2 was reduced to 15,600 μm 2 Radiative cooling devices 1 with pitches (the distance between through holes) of 5 mm, 8 mm, 10 mm, 20 mm, and 50 mm, respectively, and a radiative cooling device 1 without through holes 2 were attached to a steel plate with excess water on its surface, ensuring sufficient water remained between the radiative cooling device 1 and the steel plate. The steel plate was then heated to 65°C to promote swelling of the radiative cooling device 1, and the swelling area ratio (%) was calculated from images of the radiative cooling device 1. The relationship between heating time (H) and swelling area ratio (%) was then determined. The results are shown in Figures 5 and 6.

[0041] In the graph in Figure 5, the horizontal axis represents the heating time (H) of the steel plate, and the vertical axis represents the blister area ratio (%). As shown in Figure 5, it is clear that the radiative cooling device 1 without through-holes 2 shows a rapid increase in the blister area ratio in a short period of time, whereas the radiative cooling device 1 with through-holes 2 shows a suppressed increase in the blister area ratio.

[0042] Fig. 6 is a graph showing the relationship between the pitch (mm) and the blister area ratio (%) when an accelerated blister test was conducted on a sheet of 250 mm x 250 mm. As shown in Fig. 6, when the spacing between the through holes was set to 5 mm to 8 mm, almost no blistering occurred, and it is clear that favorable gas discharge properties were obtained.

[0043] (Relationship between hole area ratio and blister area ratio) Based on the data obtained from the accelerated swelling test, the relationship between the hole area ratio of the through holes 2 and the swelling area ratio was determined. The hole area ratio of the through holes 2 was calculated as the hole area of ​​the through holes 2 per unit area, with a square area of ​​50 mm × 50 mm being the unit area. The results are shown in Figure 7. In the graph of Figure 7, the horizontal axis represents the hole area ratio (%) and the vertical axis represents the swelling area ratio (%). As shown in Figure 7, when the hole area ratio of the through holes 2 was set to 0.12% to 0.28%, it is clear that almost no swelling occurred and favorable gas discharge properties were obtained. Note that when the hole area ratio was 0.28% or more, the gas discharge properties were good, but the radiative cooling effect of the radiative cooling device 1 may not be sufficient. [Explanation of symbols]

[0044] 1 Radiation cooling device 10 Protrusion 12 Top 2 through holes B Base material

Claims

1. A sheet-like radiative cooling device attached to a substrate, A large number of through holes are formed in the sheet-like radiative cooling device, the through-hole is formed at the top of a protruding portion that protrudes toward the opposite side to the surface facing the base material, The protrusion height is 100 μm or more, A radiative cooling device, wherein the through-holes have a hole area of ​​15,600 μm 2 or more.

2. 10. The radiative cooling device of claim 1 , wherein the substrate is a zinc-treated substrate.

3. The radiative cooling device according to claim 1, wherein the hole area ratio of the through holes is 0.12% to 0.28%.

4. 2. The radiative cooling device of claim 1, wherein the spacing between the through holes is 5 mm to 8 mm.

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