JP2019168174A - Radiation cooling device - Google Patents

Abstract

To provide a radiation cooling device that can increase cooling capacity.SOLUTION: A radiation cooling device is provided with an infrared radiation layer A for radiating infrared ray IR from a radiation plane H, and a light reflection layer B positioned on an opposite side to a present side of the radiation plane H in the infrared radiation layer A while both being laminated. The infrared radiation layer A is a magnesium oxide with a thickness of 0.015 mm or more.SELECTED DRAWING: Figure 1

Description

  The present invention provides a radiation in which an infrared radiation layer that radiates infrared light from a radiation surface and a light reflection layer that is positioned on the opposite side of the radiation surface on the side where the radiation surface is present are stacked. The present invention relates to a cooling device.

  Such a radiation cooling device transmits infrared light radiated from the radiation surface of the infrared radiation layer through an atmospheric window (for example, an infrared wavelength band having a wavelength of 8 to 14 μm and high atmospheric transmittance). It is used for cooling various cooling objects, such as cooling a cooling object located on the opposite side of the light reflection layer from the infrared radiation layer.

By the way, the light reflecting layer reflects light (visible light, ultraviolet light, infrared light) transmitted through the infrared radiation layer and emits it from the radiation surface, thereby transmitting light (visible light, Ultraviolet light and infrared light) are projected onto the object to be cooled and the object to be cooled is prevented from being heated.
In addition to the light transmitted through the infrared radiation layer, the light reflection layer also has a function of reflecting infrared light radiated from the infrared radiation layer to the existence side of the light reflection layer toward the infrared radiation layer. However, in the following description, it is assumed that the light reflection layer is provided to reflect light (visible light, ultraviolet light, infrared light) transmitted through the infrared radiation layer.

As a first conventional example of such a radiation cooling device, the infrared radiation layer is composed of a multilayer structure composed of a layer of SiO _2, a layer of MgO and a layer of Si ₃ N ₄ or glass (optical glass). There is something like that (see, for example, Patent Document 1).
Incidentally, in the cited document 1, in the case where the infrared radiation layer has a multilayer structure composed of a layer of SiO _2, a layer of MgO and a layer of Si ₃ N ₄ , the description of the thickness of each layer is omitted. . Moreover, when the infrared radiation layer is made of glass (optical glass), it is described that the thickness of the glass is 0.1 mm to 10 mm.

As a second conventional example of a radiant cooling device, there is one in which an infrared radiation layer is configured in a laminated configuration including an MgO layer and an SiO layer (see, for example, Patent Document 2).
Incidentally, in Patent Document 2, as the form of an infrared radiation layer including an MgO layer and an SiO layer, a first layer of MgO having a film thickness 1 of 200 to 1800 nm and an SiO 2 film having a film thickness of 1400 to 1600 nm are disclosed. A first layer of MgO having a thickness of 780 to 1080 nm, a second layer of SiO having a thickness of 50 to 170 nm, a third layer of MgO having a thickness of 1375 to 1775 nm, and , A second embodiment including a fourth layer of SiO having a thickness of 1500 to 1700 nm, a first layer of MgO having a thickness of 560 to 1060 nm, a second layer of SiO having a thickness of 50 to 150 nm, and a thickness of A third mode including a third layer of MgO having a thickness of 1600 to 2000 nm, a fourth layer of SiO having a thickness of 700 to 900 nm, and a fifth layer of a-Si having a thickness of 540 to 620 nm is described.

US Patent Application Publication No. 2015/0338175 JP-A-7-174917

In a radiant cooling device, it is desired to exhibit a large cooling capacity, such as to exhibit a cooling capacity even under sunlight.
That is, the inventor has researched and developed a radiation cooling device that exhibits a large cooling capacity by configuring an infrared radiation layer using a layer made of SiO ₂ such as quartz glass, quartz, white plate glass, etc. It is desired to obtain a larger cooling capacity than when an infrared radiation layer is formed using a layer of SiO ₂ .

For example, since white glass has a high radiation rate in an atmospheric window (wavelength of 8 to 14 μm and high infrared transmittance), white glass is used for infrared radiation. By configuring the layers, a radiant cooling device that exhibits a large cooling capacity can be configured.
However, the white plate glass also has a large thermal radiation in a wavelength band in which the thermal radiation from the atmosphere outside the atmospheric window (infrared wavelength band where the wavelength is 8 to 14 μm and the atmospheric transmittance is high) is large. It becomes a hindrance in increasing ability.
In other words, according to Kirchhoff's law, the light emissivity and the light absorptance are the same, so that the air from the atmosphere outside the atmospheric window (infrared wavelength band where the wavelength is 8 to 14 μm and the atmospheric transmittance is high) is removed. Having a high emissivity in a wavelength band in which thermal radiation is large is an obstacle to increasing the cooling capacity because it absorbs the thermal radiation of the atmosphere and is heated.

  The present invention has been made in view of the above circumstances, and an object thereof is to provide a radiant cooling device capable of increasing the cooling capacity.

The radiant cooling device of the present invention includes an infrared radiation layer that radiates infrared light from a radiation surface, and a light reflection layer that is positioned on the opposite side of the radiation surface on the side where the radiation surface exists. It is provided and its characteristic configuration is
The infrared radiation layer is magnesium oxide having a thickness of 0.015 mm or more.

  That is, as a result of intensive studies by the inventor of the present invention, it has been found that if the infrared radiation layer is made of magnesium oxide and the thickness thereof is 0.015 mm or more, the cooling capacity can be increased. .

  That is, magnesium oxide having a thickness of 0.015 mm or more has a high emissivity at a wavelength corresponding to an atmospheric window in the range of 8 μm to 14 μm, and also has a high emissivity from the atmosphere outside the atmospheric window. In order to find that the infrared radiation layer is composed of magnesium oxide having a thickness of 0.015 mm or more, the cooling capacity can be increased. It has come.

  In addition, although it is disclosed in the second conventional example, it has been shown in the prior art that a layer of magnesium oxide (MgO) is used to constitute the infrared radiation layer. In the third embodiment, the total thickness of the magnesium oxide (MgO) layer is in the range of 2160 nm to 3060 nm, and the total thickness of the magnesium oxide (MgO) layer is considerably smaller than 0.015 mm. Therefore, in the past, it has been disclosed that a large cooling capacity can be obtained by setting the thickness of the magnesium oxide constituting the infrared radiation layer to 0.015 mm or more, such as not contributing to an increase in the radiation cooling capacity. Not.

  In short, according to the characteristic configuration of the radiant cooling device of the present invention, the cooling capacity can be increased.

  The further characteristic structure of the radiation cooling device of this invention exists in the point whose thickness of the said infrared radiation layer is 0.04 mm or more.

  That is, magnesium oxide having a thickness of 0.04 mm or more has a considerably high radiation rate at a wavelength corresponding to an atmospheric window in the range of 8 μm to 14 μm, and also has a high radiation rate from the atmosphere outside the atmospheric window. It has been found that a large cooling capacity can be obtained because light in the wavelength band is reflected without much absorption.

  In short, according to the further characteristic configuration of the radiant cooling device of the present invention, a large cooling capacity can be obtained.

  The further characteristic structure of the radiation cooling device of this invention exists in the point whose thickness of the said infrared radiation layer is 0.1 mm or more.

  That is, magnesium oxide having a thickness of 0.1 mm or more has a sufficiently high emissivity at a wavelength corresponding to an atmospheric window in the range of 8 to 14 μm, and also has an emissivity from the atmosphere outside the atmospheric window. It has been found that a larger cooling capacity can be obtained because light in the high wavelength range is reflected without much absorption.

  In short, according to the further characteristic configuration of the radiant cooling device of the present invention, a larger cooling capacity can be obtained.

    The further characteristic structure of the radiation cooling device of this invention exists in the point whose thickness of the said infrared radiation layer is 0.5 mm-1 mm.

  That is, magnesium oxide having a thickness of 0.5 mm to 1 mm has a sufficiently high emissivity in most of the wavelength range corresponding to the atmospheric window in the range of 8 μm to 14 μm, and is outside the atmospheric window. As a result, light in the wavelength region having a high emissivity from the atmosphere is reflected without being absorbed so much, and it has been found that a sufficiently large cooling capacity can be obtained.

  In short, according to the further characteristic configuration of the radiant cooling device of the present invention, a sufficiently large cooling capacity can be obtained.

  A further characteristic configuration of the radiation cooling device of the present invention is that the light reflection layer is laminated using the infrared radiation layer as a substrate.

That is, since the light reflection layer is laminated using the infrared radiation layer as a substrate, the overall configuration can be simplified, and the overall configuration can be made thinner.
By the way, when laminating the light reflecting layer using the infrared radiation layer as a substrate, when forming the light reflecting layer into a layered structure, for example, each layer forming the light reflecting layer is formed by sputtering or the like. Lamination is done sequentially.

  In short, according to the further characteristic configuration of the radiant cooling device of the present invention, the overall configuration can be simplified.

In a further characteristic configuration of the radiation cooling device of the present invention, the light reflection layer is silver or a silver alloy,
The adhesion layer is laminated between the infrared radiation layer and the light reflection layer.

That is, since the light reflecting layer is silver or a silver alloy, the light transmitted through the infrared radiation layer can be appropriately reflected.
In addition, since the adhesion layer that adheres magnesium oxide and silver or a silver alloy is laminated between the infrared radiation layer and the light reflection layer, the infrared radiation layer and the light reflection layer can be appropriately laminated.

  In short, according to the further characteristic configuration of the radiation cooling device of the present invention, the light transmitted through the infrared radiation layer can be appropriately reflected, and the infrared radiation layer and the light reflection layer can be appropriately laminated. .

Diagram showing the configuration of the radiant cooling device Graph showing emissivity of radiant cooling device Graph showing atmospheric radiation intensity The figure which shows the structure of a light reflection layer The figure which shows the structure of a light reflection layer The figure which shows the structure of a light reflection layer The figure which shows the structure of a light reflection layer The figure which shows the structure of a light reflection layer The figure which shows the structure of a light reflection layer The figure which shows the structure of a light reflection layer Diagram showing the structure of the UV reflective multilayer film The figure which shows the implementation structure of a radiation cooling device The figure which shows the comparison constitution of the radiation cooling device Graph showing emissivity of radiation cooling device of comparative configuration A graph showing the cooling capacity of the implementation configuration and the comparison configuration Graph showing solar energy Schematic explaining the relationship between the radiant cooling device and the wind of the outside air Table showing the equilibrium temperature of the implementation in the absence of convective heat transfer Table showing the equilibrium temperature of the comparison configuration without convective heat transfer Table showing the equilibrium temperature of the working configuration and comparative configuration with convective heat transfer Diagram showing a specific example of a radiant cooling device The figure which shows another specific example of a radiant cooling device Graph showing the absorption rate in a specific example of a radiant cooling device

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
[Configuration of Radiation Cooling Device]
As shown in FIG. 1, the radiation cooling device CP includes an infrared radiation layer A that radiates infrared light IR from the radiation surface H, and a side opposite to the side where the radiation surface H is present in the infrared radiation layer A. The light reflection layer B to be positioned is provided in a laminated state.

Therefore, the radiant cooling device CP reflects a part of the light L incident on the radiant cooling device CP (for example, a part of sunlight) on the radiation surface H of the infrared radiation layer A. The light (ultraviolet light, etc.) transmitted through the infrared radiation layer A among the light L incident on the radiation cooling device CP is reflected by the light reflection layer B.
In the present embodiment, light means an electromagnetic wave having a wavelength of 10 nm to 20000 nm. That is, the light L includes ultraviolet light, infrared light IR, and visible light.

  And the heat input (for example, heat input by the heat conduction from the cooling object D) to the radiation cooling device CP from the cooling object D located on the opposite side to the existence side of the infrared radiation layer A in the light reflection layer B is performed. The cooling object D is cooled by being converted to infrared IR by the infrared radiation layer A and radiating.

The infrared radiation layer A is composed of magnesium oxide (MgO).
Magnesium oxide (MgO) may be a single crystal, a polycrystal, or a sintered body, and may further be a paint in which a powder of magnesium oxide (MgO) is dispersed in a resin.
However, the present embodiment will be described on the assumption that single crystal or polycrystalline magnesium oxide (MgO) is used as a substrate on which the light reflecting layer B is laminated, as will be described later.

The light reflecting layer B is made of silver or a silver alloy having a thickness of about 300 nm.
By the way, as the “silver alloy”, an alloy in which any of copper, palladium, gold, zinc, tin, magnesium, nickel, and titanium is added to silver, for example, about 0.4 to 4.5 mass% is used. Can do. As a specific example, “APC-TR (made by Furuya Metal)” which is a silver alloy prepared by adding copper and palladium to silver can be used.

In the present embodiment, the light reflection layer B will be described as being composed of silver having a thickness of 300 nm.
That is, using the infrared radiation layer A of magnesium oxide (MgO) as a substrate, the light reflection layer B is laminated by vapor deposition or the like.

  In the radiation cooling device CP of the present embodiment, the thickness of the infrared radiation layer A is 0.015 mm or more, preferably 0.04 mm or more, more preferably 0.1 mm. Most preferably, the thickness is 0.5 mm to 1 mm.

FIG. 2 shows a case where the thickness of magnesium oxide (MgO) is changed in the radiation cooling device CP including the light reflection layer B having a thickness of 300 nm and the infrared radiation layer A of magnesium oxide (MgO). Shows the change in the radiation rate of light.
Since the absorptance and the emissivity are equal according to Kirchhoff's law, a wavelength region with a high emissivity is a wavelength region with a high absorptance.
FIG. 3 shows the radiant intensity of the atmosphere when the temperature is 30.degree.

Considering FIGS. 2 and 3, magnesium oxide (MgO) exhibits a large thermal radiation at an atmospheric window having a wavelength of 8 to 14 μm, and has a high emissivity from the atmosphere outside the atmospheric window. It can be seen that the material reflects well without absorbing light.
If the thickness is 0.015 mm or more, the emissivity at the atmospheric window is increased, and if the thickness is 0.04 mm or more, the emissivity at the atmospheric window is further increased. If the thickness is 0.1 mm or more, the emissivity at the atmospheric window is further increased, and if the thickness is 0.5 mm to 1 mm, the emissivity is sufficiently high at the atmospheric window, and the range is 8 to 14 μm. It can be seen that the emissivity (absorption rate) in the wavelength region outside the range is sufficiently low.

  Therefore, the thickness of the infrared radiation layer A is set to 0.015 mm or more, preferably 0.04 mm or more, more preferably 0.1 mm or more, and most preferably the thickness. By setting the thickness to 0.5 mm to 1 mm, it is possible to configure the radiant cooling device CP having a large cooling capacity.

[Another form of light reflection layer]
As described above, the light reflecting layer B can be composed of silver or a silver alloy. However, as shown in FIGS. 4 to 10, the light reflecting layer B can have various other structures.
That is, as shown in FIG. 4, as the light reflecting layer B, a first layer B1 made of silver or a silver alloy and aluminum (abbreviated as “aluminum” in the following description) or an aluminum alloy (in the following description, “aluminum alloy”). And the second layer B2 made of the abbreviation) may be configured to be stacked in a form in which the first layer B1 is positioned closer to the infrared radiation layer A.

In this case, the thickness (film thickness) of the first layer B1 is larger than 3.3 nm and not more than 100 nm, and preferably the thickness (film thickness) of the first layer B1 is not less than 50 nm and not more than 100 nm. To do.
Further, the thickness (film thickness) of the second layer B2 is set to 10 nm or more.

  As the “aluminum alloy”, an alloy obtained by adding copper, manganese, silicon, magnesium, zinc, carbon steel for mechanical structure, yttrium, lanthanum, gadolinium, and terbium to aluminum can be used.

Further, the structure shown in FIG. 4 is improved, and as shown in FIG. 5, the alloying prevention for preventing the alloying of silver or silver alloy and aluminum or aluminum alloy between the first layer B1 and the second layer B2. A configuration in which a transparent nitride film Bn as a transparent layer is provided, or a transparent oxide film Bs as an anti-alloying transparent layer is provided between the first layer B1 and the second layer B2 as shown in FIG. May be.
The transparent nitride film Bn can be configured using Si ₃ N ₄ or AlN.
As the transparent oxide film Bs, Al ₂ O ₃ , SiO ₂ , TiO ₂ , ZrO ₂ , HfO ₂ , Nb ₂ O ₅ , Ta ₂ O _5, or other oxides that can be easily formed by vapor deposition or sputtering are used. Can do.

Furthermore, as shown in FIG. 7, you may comprise in the form which provides the ultraviolet reflective multilayer film Bu in the front side of the light reflection main body layer BH comprised with silver or a silver alloy.
For example, as shown in FIG. 11, the ultraviolet reflective multilayer film Bu may have a configuration in which _two layers of SiO ₂ layers and Nb ₂ O ₅ layers are alternately stacked.

As described above, as a form in which the ultraviolet reflecting multilayer film Bu is provided, as shown in FIG. 8, in the configuration shown in FIG. 4 in which the first layer B1 and the second layer B2 are provided, the ultraviolet reflecting multilayer film Bu is provided on the front side thereof. You may comprise in the form which provides.
Similarly, as shown in FIG. 9, in the configuration shown in FIG. 5 in which a transparent nitride film Bn is provided between the first layer B1 and the second layer B2, an ultraviolet reflective multilayer film Bu is provided on the front side thereof. Further, as shown in FIG. 10, in the configuration shown in FIG. 6 in which the transparent oxide film Bs is provided between the first layer B1 and the second layer B2, an ultraviolet reflective multilayer film Bu is formed on the front side thereof. You may comprise in the form to provide.

[Consideration of Radiation Cooling Device]
As shown in FIG. 12, the radiation cooling device CP of the present invention in which the infrared radiation layer A is made of magnesium oxide (MgO) having a thickness of 1 mm and the light reflection layer B is made of silver having a thickness of 300 nm, 13, a conventional radiant cooling device CP in which the infrared radiation layer A is Tempax (registered trademark, the same applies hereinafter) having a thickness of 1 mm, and the light reflection layer B is silver having a thickness of 300 nm; The cooling capacity was compared.

  That is, the cooling capacity of the radiant cooling device CP of the present invention in which the infrared radiation layer A is magnesium oxide (MgO) having a thickness of 1 mm, and the conventional radiation in which the infrared radiation layer A is tempax having a thickness of 1 mm. The cooling capacity of the cooling device CP was determined for each of the outside air temperatures of 30 ° C., 40 ° C., and 50 ° C. without considering convective heat transfer and conduction heat transfer, and the results shown in FIG. 15 were obtained.

  Tempax is a borosilicate glass which is an example of white plate glass, has a high reflectance with respect to light having a wavelength corresponding to sunlight, and, as shown in FIG. The radiation rate of the wavelength corresponding to the so-called atmospheric window (8 to 14 μm) is high. However, Tempax also has a high radiation rate in a wavelength range smaller than the range of 8 to 14 μm that is an atmospheric window and a wavelength range larger than the range of 8 to 14 μm that is an atmospheric window.

  In FIG. 15, the vertical axis indicates the cooling capacity of the radiant cooling device CP, the horizontal axis indicates the temperature of the radiant cooling device CP, and the radiant cooling device CP in which the cooling capacity of the radiant cooling device CP of the present invention becomes zero. The temperature (equilibrium temperature) is lower than the temperature (equilibrium temperature) of the radiant cooling device CP at which the cooling capacity of the conventional radiant cooling device CP becomes zero at any of the outside air temperatures of 30 ° C., 40 ° C., and 50 ° C. Become.

That is, it can be seen that the radiant cooling device CP of the present invention can be cooled to a lower temperature than the conventional radiant cooling device CP at any of the outside air temperatures of 30 ° C., 40 ° C., and 50 ° C.
The reason for this is that, as shown in FIG. 2, the radiant cooling device CP of the present invention exhibits a large thermal radiation at an atmospheric window having a wavelength of 8 to 14 μm and a high emissivity from the atmosphere outside the atmospheric window. As shown in FIG. 14, the conventional radiant cooling device CP exhibits a large amount of heat radiation in an atmospheric window having a wavelength of 8 to 14 μm. By absorbing light in a wavelength band with high emissivity from the atmosphere outside the window.

The cooling capacity of the radiant cooling device CP was defined as the following formula (Equation 1).

P _cool (T) is the cooling capacity of the radiant cooling device CP at the temperature T, P _rad (T) is the radiation amount (radiation amount) from the radiant cooling device CP at the temperature T, P _sun is the heat input of sunlight, P _air (T _air ) is heat input by thermal radiation of the atmosphere, and T _air is the temperature of the atmosphere.
Further, each of P _rad (T), P _sun , and P _air (T _air ) is defined as the following formula (Formula 2), Formula (Formula 3), and Formula (Formula 4).

Where ε _λ is the emissivity (emissivity) of the radiation cooling device CP, I _BB (T) is the black body radiation at the temperature T, A _cooler.λ is the light absorption rate of the radiation cooling device CP, and I _sun is the solar spectrum. (Wavelength distribution of solar energy), ε _air.λ is the atmospheric emissivity, and λ is the wavelength.
FIG. 16 shows the relationship between sunlight energy and wavelength.

[Consideration in consideration of actual use environment]
Next, the radiation cooling performance of the radiation cooling device CP will be considered in consideration of the actual use environment (such as the influence of the wind). First, the calculation method will be described.
Radiant cooling performance is defined by the equilibrium temperature under the assumed conditions.
With reference to FIG. 17, the fixed condition and the changed condition in calculating the radiation cooling performance will be described. The fixed condition is a solar spectrum and an atmospheric transmittance spectrum. As for the sunlight spectrum, AM1.5 standard values were used assuming a midsummer time in midsummer. Under the conditions of AM 1.5, the sunlight intensity is 1000 W / m ² . For the atmospheric transmittance spectrum, the average value of Osaka in midsummer was used.

The changed conditions are the outside air temperature and the value of convective heat transfer. The outside air temperature was 30 ° C., 40 ° C., and 50 ° C. There are four types of convective heat transfer: “Without convective heat transfer”, “Smooth wind (0-1 m / s)”, “Slight wind (1-3 m / s)”, “Light wind (4-6 m / s)” Was assumed. Each of the four types of heat transfer coefficients (h) is 0 W / m ² K, 5 W / m ² K, 10 W / m ² K, and 15 W / m ² K.
Assuming that the radiant cooling device CP (radiant cooling material) continues at infinity, the cooling object D in the shadowed portion of the radiant cooling device CP (radiant cooling material) is the radiant cooling device CP (radiant cooling material). ) And the same temperature.

The equilibrium temperature is a temperature at which P _cool (T) = 0.
P _cool (T) including convective heat transfer is expressed by the following equation (Equation 5).

According to the above calculation method, the equilibrium temperature of the radiant cooling device CP (radiant cooling material) is set to a condition of 0 W / m ² K corresponding to the case where the outside air temperature is 30 ° C. and the heat transfer coefficient is “no convective heat transfer”. The obtained results are shown in the table of FIG.
That is, under the above conditions, when the light reflection layer B of the radiation cooling device CP (radiation cooling material) is made of silver having a thickness of 300 nm, the infrared radiation layer A composed of magnesium oxide (MgO) Equilibrium temperatures obtained by changing the thickness (thickness) to 0.001 to 10 mm are shown in the table of FIG.

From the table of FIG. 18, it can be seen that the equilibrium temperature of the radiant cooling device CP (radiant cooling material) falls below 30 ° C. when the thickness of magnesium oxide (MgO) is greater than 0.015 mm. That is, the lower limit of the thickness (thickness) of magnesium oxide (MgO) in the radiation cooling device CP (radiation cooling material) using magnesium oxide (MgO) is 0.015 mm.
In addition, if the thickness of magnesium oxide (MgO) is greater than 0.015 mm, the radiation cooling capability will not be lost at any thickness, so the thickness of magnesium oxide (MgO) is calculated to be up to 10 mm.

The radiant cooling device CP (radiant cooling material) of the present invention is cooled more than a conventional radiant cooling device CP (radiant cooling material) using a layer made of SiO ₂ such as quartz glass, quartz, white plate glass, etc., as the infrared radiation layer A. In order to increase the capacity, in order to obtain a suitable thickness of magnesium oxide (MgO) in the radiant cooling device CP (radiant cooling material) of the present invention, the radiant cooling device CP (radiant cooling material) of the present invention The equilibrium temperature is compared with the equilibrium temperature of a conventional radiant cooling device CP (radiant cooling material).

The table of FIG. 19 shows the same conditions as those for obtaining the results shown in the table of FIG. 18, and the light reflecting layer B of the radiation cooling device CP (radiation cooling material) is made of silver having a thickness of 300 nm. _The equilibrium temperature obtained by changing the thickness (thickness) of the infrared radiation layer A composed of _two layers to 0.0005 to 10 mm is shown. The SiO ₂ layer is required to be quartz.

As shown in the table of FIG. 19, when the SiO ₂ layer is quartz, the equilibrium temperature is about 13 ° C. and the lowest when the thickness is 0.01 to 0.02 mm.
However, quartz having a thickness of 0.01 to 0.02 mm is a film thickness that is most laborious to produce regardless of the method of vapor deposition, sputtering, or polishing, and is a fragile film thickness. The thickness is not practically practical.

In view of this point, the equilibrium temperature of the radiant cooling device CP (radiant cooling material) of the present invention using magnesium oxide (MgO) and the equilibrium of the conventional radiant cooling device CP (radiant cooling material) using SiO ₂ (quartz). Comparing the temperature with the table of FIG. 18 and the table of FIG. 19, when the thickness of magnesium oxide (MgO) is 0.04 mm or more, the equilibrium of the radiant cooling device CP (radiant cooling material) of the present invention is achieved. It can be seen that the temperature is lower than the equilibrium temperature of a conventional radiant cooling device CP (radiant cooling material) using SiO ₂ (quartz).

Further, when the thickness of magnesium oxide (MgO) is 0.05 mm or more, the equilibrium temperature of the radiation cooling device CP (radiation cooling material) of the present invention is further lowered, and the thickness of magnesium oxide (MgO) is 0.1 mm or more. Then, the equilibrium temperature of the radiant cooling device CP (radiant cooling material) of the present invention is considerably lower than the equilibrium temperature of the conventional radiant cooling device CP (radiant cooling material) using SiO ₂ (quartz). When the thickness of magnesium (MgO) is 0.5 mm or more, the equilibrium temperature of the radiant cooling device CP (radiant cooling material) of the present invention is the lowest temperature (-1.9 ° C.).

  Therefore, the thickness of magnesium oxide (MgO) in the radiation cooling device CP (radiation cooling material) of the present invention is preferably 0.015 mm or more, preferably 0.04 mm or more, and more preferably. Is preferably 0.1 mm or more, and most preferably 0.5 mm to 1 mm.

Next, at outside temperatures of 30 ° C., 40 ° C., and 50 ° C., the heat transfer coefficient is 0 W / m ² K corresponding to “the case where there is no convective heat transfer”, “smooth wind (0-1 m / s ) ”Corresponding to 5 W / m ² K condition,“ 10 W / m ² K condition corresponding to “very light wind (1-3 m / s)”, and “light wind (4-6 m / s)”. The table | surface of FIG. 20 shows the result of having calculated | required the equilibrium temperature in the conditions of 15 W / m < ² > K about the radiation cooling device CP (radiation cooling material) of this invention, and the conventional radiation cooling device CP (radiation cooling material).
The calculation method is obtained based on the equation (Equation 5) in the same manner as the calculation method for obtaining the results shown in the table of FIG.

In the table of FIG. 20, as an equilibrium temperature of the conventional radiation cooling device CP (radiation cooling material), the light reflection layer B is made of silver having a thickness of 300 nm, and an infrared radiation layer composed of a layer of SiO _2. The equilibrium temperature in the case where the thickness (thickness) of A is 1 mm that can sufficiently ensure the mechanical strength, and the infrared light composed of a layer of SiO ₂ with the light reflecting layer B made of silver having a thickness of 300 nm. The equilibrium temperature when the thickness (thickness) of the radiation layer A is 0.01 mm is described.
Further, as the equilibrium temperature of the radiation cooling device CP (radiation cooling material) of the present invention, the thickness of the infrared radiation layer A made of magnesium oxide (MgO) is used in which the light reflection layer B is made of silver having a thickness of 300 nm. The equilibrium temperature when the thickness (thickness) is 1 mm is described.

Considering the table of FIG. 20, magnesium oxide (MgO) is used regardless of whether the heat transfer coefficient is 0 W / m ² K, 5 W / m ² K, 10 W / m ² K, or 15 W / m ² K. The equilibrium temperature of the radiant cooling device CP (radiant cooling material) of the present invention is lower than the equilibrium temperature of the conventional radiant cooling device CP (radiant cooling material) using SiO ₂ . Further, it should be noted that the cooling effect of the radiant cooling device CP (radiant cooling material) of the present invention using magnesium oxide (MgO) when the outside air temperature (outside air temperature) is high is the same as that of the conventional one using SiO _2. It is to be larger than the radiation cooling device CP (radiation cooling material).

In recent years, many lives have been lost in various parts of the world due to the effects of temperature higher than the body temperature caused by heat waves and heat islands. However, the radiant cooling device CP (radiant cooling material) of the present invention using magnesium oxide (MgO) is used outdoors. When applied to cooling technology in a non-powered area, many lives can be saved.
Here, the case where the wind is strong “light wind (4-6 m / s)” (heat transfer coefficient: 15 W / m ² K) is considered. When the wind is strong, the heat transfer coefficient increases, so the temperature of the radiant cooling device CP (radiant cooling material) is close to the outside air temperature, and the difference in the materials that make up the radiant cooling device CP (radiant cooling material) The difference is less affected.

However, problems such as heat waves and heat islands that frequently occur in various parts of the world in recent years generally occur when there is no wind.
Radiant cooling device CP (radiant cooling material) of the present invention using magnesium oxide (MgO) when “smooth wind (0-1 m / s)” (heat transfer coefficient: 5 W / m ² K) corresponding to no wind condition The equilibrium temperature of) is about the body temperature (36.8 ° C.) even when the outside air temperature is 50 ° C., which is overwhelming than the equilibrium temperature of the conventional radiation cooling device CP (radiation cooling material) using SiO _2. Since the temperature is lowered, the practical value is high.

[Confirmation results]
Next, a radiation cooling device CP (radiation cooling material) using magnesium oxide (MgO) was actually created, and the experimental results actually measured for the created radiation cooling device CP (radiation cooling material) were actually created. By comparing with the calculation result obtained by calculating the optical characteristics of the radiation cooling device CP (radiation cooling material), it is confirmed that the calculation method in the above consideration is correct.

As the radiation cooling device CP (radiation cooling material), as shown in FIG. 21, the light reflection layer B is made of silver having a thickness of 300 nm, and the infrared radiation layer A is made of magnesium oxide (MgO having a thickness of 0.5 mm). 22) and the light reflecting layer B is made of silver having a thickness of 300 nm, and the infrared emitting layer A is made of magnesium oxide (MgO) having a thickness of 0.5 mm, as shown in FIG. And the 2nd test body which arrange | positioned the contact | adherence layer E between the infrared radiation layer A and the light reflection layer B was created.
The adhesion layer E includes a silver adhesion layer E1 which is a 30 nm layer of Al ₂ O ₃ and a reaction prevention layer E2 which is a 30 nm layer of HfO _2. The silver adhesion layer E1 is a layer which adheres to silver (Ag). The reaction prevention layer E2 is a layer that prevents the reaction between Al ₂ O ₃ and MgO.

  Incidentally, when a metal film is formed on a magnesium oxide (MgO) substrate, it can be considered that the adhesion layer E is necessary. However, in practice, even if the adhesion layer E is not provided, magnesium oxide (MgO ) Can be formed on the substrate. However, it can be considered that providing the adhesive layer E is better in the long term.

Since there was almost no difference in the absorptance actually measured about the 1st test body and the 2nd test body, and the absorptivity calculated about the 1st test body and the 2nd test body, about the 2nd test body The results are shown in FIG. 23 as a representative.
As shown in FIG. 23, the experimental result of the absorptivity measured for the second specimen and the calculation result of the absorptance calculated for the second specimen are substantially the same.
From the viewpoint of suppressing the absorption of thermal radiation in the atmosphere, it is better that the absorption rate on the longer wavelength side than 15 μm is smaller, but it is understood that the experimental result is more ideal than the calculation result. .
Therefore, since the absorption rate and the radiation rate are equal, it was confirmed that the calculation result shown in FIG. 2 is correct. Moreover, it has confirmed that the calculation result shown in FIG.14, FIG.15, FIG.18-FIG.

[Another embodiment]
Hereinafter, other embodiments are listed.
(1) In the above embodiment, the case where the light reflection layer B is laminated using the infrared radiation layer A as a substrate is illustrated, but the light reflection is performed in a form of lamination on another substrate different from the infrared radiation layer A. The layer B may be formed, and the infrared radiation layer A and the light reflection layer B may be laminated. In this case, a slight gap may exist between the infrared radiation layer A and the light reflection layer B as long as heat transfer is possible.

(2) In the above embodiment, the case where the infrared radiation layer A is composed of single crystal or polycrystalline magnesium oxide (MgO) is exemplified, but magnesium oxide (MgO) is cheaper than single crystal or polycrystalline. Further, it may be a sintered body, or may be a paint in which powdered magnesium oxide (MgO) is dispersed in a resin.

  Note that the configurations disclosed in the above-described embodiments (including other embodiments, the same applies hereinafter) can be applied in combination with the configurations disclosed in the other embodiments as long as no contradiction arises. The embodiment disclosed in this specification is an exemplification, and the embodiment of the present invention is not limited to this. The embodiment can be appropriately modified without departing from the object of the present invention.

A Infrared radiation layer B Light reflection layer E Adhesion layer H Radiation surface

Claims (6)

A radiation cooling device in which an infrared radiation layer that radiates infrared light from a radiation surface and a light reflection layer that is positioned on the opposite side of the radiation surface on the side where the radiation surface exists are provided in a stacked state. And
A radiation cooling device, wherein the infrared radiation layer is magnesium oxide having a thickness of 0.015 mm or more.   The radiation cooling device according to claim 1, wherein the infrared radiation layer has a thickness of 0.04 mm or more.   The radiation cooling device according to claim 1 or 2, wherein the infrared radiation layer has a thickness of 0.1 mm or more.   The radiant cooling device according to claim 1, wherein the infrared radiation layer has a thickness of 0.5 mm to 1 mm.   The radiation cooling device according to any one of claims 1 to 4, wherein the light reflection layer is laminated using the infrared radiation layer as a substrate. The light reflecting layer is silver or a silver alloy,
The radiation cooling device according to claim 5, wherein an adhesion layer is laminated between the infrared radiation layer and the light reflection layer.

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