CN116816242A - Color-controllable radiation refrigeration transparent window structure - Google Patents

Abstract

The invention relates to the technical field of optical passive radiation refrigeration, and discloses a color-controllable radiation refrigeration transparent window structure, which includes a glass layer. One side of the glass layer is a solar spectrum reflective layer, and the other side is a thermal infrared emitting layer. The solar spectrum reflective layer is (Al ₂ O ₃ /Ag (10nm)/TiO ₂ ) ⁿ , and the thermal infrared emitting layer is SiO ₂ or PDMS. The color-controlled radiation refrigeration transparent window structure of the present invention can achieve a passive radiation refrigeration effect. In winter, the rotating shaft is used to turn the glass over, and it has high reflectivity in both near-ultraviolet and thermal infrared, thus achieving a heat preservation effect.

Description

A color-controllable radiation cooling transparent window structure

Technical field

The invention relates to the technical field of optical passive radiation refrigeration, specifically a color-controllable radiation refrigeration transparent window structure.

Background technique

As the problem of global resource scarcity emerges, it is imperative to reduce energy loss. In the outer envelope structure of modern buildings, the weakest link in thermal insulation and thermal insulation is the door, window and curtain wall. Reducing the energy consumption caused by heat transfer of doors, windows and curtain walls has become the key to reducing building operation energy consumption. Similarly, in summer, a lot of heat enters the car through the car windows, and the driver has to use the air conditioner for cooling. Reducing the energy consumption of the car air conditioner has also become the key to reducing the energy consumption of the car. Therefore, to reduce cooling energy consumption, automobile windows and architectural glass are required to have both high solar reflection and good heat dissipation functions in summer, and to prevent excessive indoor radiation from causing heat loss in winter.

The atmospheric window (AW) refers to some bands of celestial radiation that can penetrate the atmosphere. Due to the absorption and reflection of radiation by various particles in the earth's atmosphere, only celestial radiation within certain wavebands can reach the ground. The main spectral bands of the atmospheric window include: microwave band (0.3~10GHz/0.03-1m), thermal infrared band (8μm~14μm), mid-infrared band (3.5μm~5.5μm), near-ultraviolet, visible light and near-infrared band (0.3 μm～1.3μm, 1.5μm～2.5μm). The transmittance of the atmospheric transparent window (8 μm ~ 13 μm) is very high in the thermal infrared band of 8 μm ~ 13 μm, so this band is called the atmospheric transparent window. Therefore, when the designed film provides high emissivity in this band and low absorption rate in other bands, it can emit excess heat to outer space, thereby achieving the purpose of passive radiation cooling.

The solar spectrum is an absorption spectrum of different wavelengths. The wavelength range is approximately 0.28μm ~ 4μm, which is divided into visible light and invisible light. After visible light is scattered, it is divided into seven colors: red, orange, yellow, green, cyan, blue, and violet. When concentrated, it becomes white light. Invisible light is divided into two types: infrared and ultraviolet. The surface temperature of the sun is about 5800K. The sun at this temperature can be approximately regarded as a black body. 99% of the solar radiation reaching the earth's outer atmosphere is distributed in the 0.15μm ~ 4μm band, and only about 45% can pass through the atmospheric window to reach the ground, and This part is mainly distributed in the 0.2μm ~ 2.5μm band. Therefore, by achieving a strong solar spectrum reflectivity and a low solar spectrum transmittance within the solar spectrum range, the purpose of passive radiation cooling can be achieved.

Therefore, passive radiative cooling technology is a technology that absorbs heat from objects and emits it to outer space through a transparent window in the atmosphere. It has the advantages of no energy consumption throughout the day, green economy and environmental protection. Its cooling power can reach 100W/m-2. The passive radiation cooling model should have a high thermal infrared emissivity in the atmospheric transparent window, so that the heat generated inside can be emitted in time, and meet the conditions of high reflectivity in the near-infrared band (0.78μm<λ<2.5μm) of the solar spectrum. To prevent the cooling model itself from being heated by sunlight, it maximizes the radiant cooling effect under direct sunlight.

The ideal structure for radiative cooling is theoretically designed to have high transmittance in the visible band (VIS), high emissivity in the AW, and reflect light in the ultraviolet (UV) to the near-infrared (NIR) state. In summer, sunlight is incident from the outside, only visible light enters the room, and NIR is blocked. In winter, both visible light and NIR are transmitted into the room.

Contents of the invention

The invention provides a color-controllable radiation refrigeration transparent window structure, which can realize a radiation refrigeration structure that is transparent in the visible spectrum, reflects in the invisible solar spectrum range, and emits its thermal energy through AW, which is suitable for automobiles or buildings. Glass is a satisfactory result.

The technical solution of the present invention is a color-controllable radiation cooling transparent window structure, which includes a glass layer. On one side of the glass layer is a solar spectrum reflective layer, and on the other side is a thermal infrared emitting layer. The solar spectrum reflective layer is (Al ₂ O ₃ /Ag (10nm)/TiO ₂ ) ⁿ , the thermal infrared emitting layer SiO ₂ or PDMS (polydimethylsiloxane).

The Al ₂ O ₃ is selected to be 50nm, Ag is selected to be 10nm, TiO ₂ is selected to be 15nm, PDMS is selected to be 100 μm, SiO ₂ is 2 μm, and the value of n is 2.

Using 2μmSiO ₂ /glass/(50nmAl ₂ O ₃ /10nmAg/15nmTiO ₂ ) ² structure can increase the average surface emissivity by 45.02%. The net cooling power at night is 144W/m ² higher than that during the day. At thermal equilibrium, the maximum temperature rise during the day is The highest temperature is 46.7℃, and the minimum temperature drop at night is 7.0℃. Using the 100μm PDMS/glass/(50nmAl ₂ O ₃ /10nmAg/15nmTiO ₂ ) ² structure can increase the average surface emissivity by 90.349%. The net cooling power at night is 89.63W/m ² higher than that during the day. The minimum temperature during the day drops to 3.3℃, the minimum temperature drop at night is 11.3℃. Both structures can achieve passive radiation cooling effects. In winter, the rotating shaft is used to flip the glass. It has high reflectivity in both near-ultraviolet and thermal infrared, which has a thermal insulation effect.

Description of the drawings

Figure 1 is a schematic diagram of the model of the film system structure d ₃ SiO ₂ /Glass/(d ₁ Al ₂ O ₃ /Ag (10nm)/d ₂ TiO ₂ ) ² of the present invention (the film thickness of Al ₂ O ₃ is d ₁ , TiO The film thickness d ₂ of ₂ , the film thickness d ₃ of SiO ₂ ,);

Figure 2a is a comparison chart of the transmittance of asymmetric periodic structures and symmetric periodic structures in the 0.28 μm ~ 2.5 μm band;

Figure 2b is a comparison chart of the reflectivity of asymmetric periodic structures and symmetric periodic structures in the 0.28 μm ~ 2.5 μm band;

Figure 2c is a comparison chart of the absorption rates of asymmetric periodic structures and symmetric periodic structures in the 0.28 μm ~ 2.5 μm band;

Figure 3 shows the transmittance of the (d ₁ Al ₂ O ₃ /Ag (10nm)/d ₂ TiO ₂ ) ² (d ₁ =80nm and d ₂ =5~75nm) composite film structure;

Figure 4 shows the transmittance of the (d ₁ Al ₂ O ₃ /Ag (10nm)/d ₂ TiO ₂ ) ² (d ₁ =10~80nm and d ₂ =55nm) composite thin film structure;

Figure 5 shows the direct transmittance/% of the composite film of (d ₁ Al ₂ O ₃ /Ag (10nm)/d ₂ TiO ₂ ) ² (d ₁ =10~80nm and d ₂ =5~75nm);

Figure 6 shows the reflectance of the (d ₁ Al ₂ O ₃ /Ag (10nm)/d ₂ TiO ₂ ) ² (d ₁ =80nm and d ₂ =5~75nm) composite thin film structure;

Figure 7 shows the reflectivity of (d ₁ Al ₂ O ₃ /Ag (10nm)/d ₂ TiO ₂ ) ² (d ₁ =10~80nm and d ₂ =55nm) composite thin film structure;

Figure 8 shows the direct reflectance/% of the composite film of (d ₁ Al ₂ O ₃ /Ag (10nm)/d ₂ TiO ₂ ) ² (d ₁ =10~80nm and d ₂ =5~75nm);

Figure 9 shows the absorbance of the (d ₁ Al ₂ O ₃ /Ag (10nm)/d ₂ TiO ₂ ) ² (d ₁ =80nm and d ₂ =5~75nm) composite film structure;

Figure 10 shows the absorption rate of (d ₁ Al ₂ O ₃ /Ag (10nm)/d ₂ TiO ₂ ) ² (d ₁ =10~80nm and d ₂ =55nm) composite film structure;

Figure 11 shows the direct absorption ratio/% of the composite film of (d ₁ Al ₂ O ₃ /Ag (10nm)/d ₂ TiO ₂ ) ² (d ₁ =10~80nm and d ₂ =5~75nm);

Figure 12a, Figure 12b and Figure 12c screen the optical properties of five groups of structures for transmittance, reflectivity and absorptivity respectively;

Figure 13a shows the transmittance optical properties of the (Al ₂ O ₃ (50nm)/Ag (10nm)/TiO ₂ (15nm)) ⁿ (n=1, 2 and 3) film system structure; Figure 13b shows the (Al ₂ O ₃ (50nm)/Ag(10nm)/TiO ₂ (15nm)) ⁿ (n=1, 2 and 3) reflectivity optical properties of the film structure; Figure 13c is (Al ₂ O ₃ (50nm)/Ag (10nm) /TiO ₂ (15nm)) ⁿ (n=1, 2 and 3) absorbance optical properties of the film structure; Figure 14a is d ₃ SiO ₂ /(Al ₂ O ₃ (50nm)/Ag (10nm)/TiO ₂ (15nm)) ² (d ₃ =0~2.4μm) transmittance optical properties of the composite thin film structure;

Figure 14b shows the reflectivity optical performance of the composite thin film structure of d ₃ SiO ₂ /(Al ₂ O ₃ (50nm)/Ag (10nm)/TiO ₂ (15nm)) ² (d ₃ =0～2.4μm);

Figure 14c shows the absorbance optical properties of the composite thin film structure of d ₃ SiO ₂ /(Al ₂ O ₃ (50nm)/Ag (10nm)/TiO ₂ (15nm)) ² (d ₃ =0～2.4μm);

Figure 15 shows the photothermal effect of SiO ₂ film thickness on the composite thin film structure of d ₃ SiO ₂ /(Al ₂ O ₃ (50nm)/Ag (10nm)/TiO ₂ (15nm)) ² (d ₃ =0～2.4μm) Performance impact/%;

Figure 16a shows the transmittance optical properties of the composite thin film structure of 100μm PDMS/(Al ₂ O ₃ (50nm)/Ag (10nm)/TiO ₂ (15nm)) ² ;

Figure 16b shows the reflectance optical performance of the composite thin film structure of 100μm PDMS/(Al ₂ O ₃ (50nm)/Ag (10nm)/TiO ₂ (15nm)) ² ;

Figure 16c shows the absorbance optical properties of the composite thin film structure of 100μm PDMS/(Al ₂ O ₃ (50nm)/Ag (10nm)/TiO ₂ (15nm)) ² ;

Figure 17 shows the effect of PDMS solvent ratio on the photothermal performance of the composite film structure of 100μm/(Al ₂ O ₃ (50nm)/Ag (10nm)/TiO ₂ (15nm)) ² /%;

Figure 18a shows the relationship between the net cooling power and the temperature difference on the coating surface when SiO ₂ is used as the emissive layer for cooling during the day;

Figure 18b shows the relationship between the net cooling power and the temperature difference on the coating surface when SiO ₂ is used as the emissive layer for night cooling;

Figure 19a shows the relationship between the net cooling power and the temperature difference on the coating surface when cooling 19PDMS as the emissive layer during the day;

Figure 19b shows the relationship between the net cooling power and the temperature difference on the coating surface when PDMS is used as the emissive layer for night cooling;

Figure 20a shows the transmission color of the composite film of (d ₁ A _l2 O ₃ /Ag (10nm)/d ₂ TiO ₂ ) ² (d ₁ =10~80nm and d ₂ =5~75nm);

Figure 20b shows the transmission color and Lab value corresponding to the film thickness used in the embodiment of the present invention;

Figure 21a shows the reflection color of the composite film of (d ₁ A _l2 O ₃ /Ag (10nm)/d ₂ TiO ₂ ) ² (d ₁ =10~80nm and d ₂ =5~75nm);

Figure 21b shows the reflection color and Lab value corresponding to the film thickness used in the embodiment of the present invention;

Figure 22a and Figure 22b respectively show the transmission and reflection colors and Lab of d ₃ SiO ₂ /(Al ₂ O ₃ (50nm)/Ag (10nm)/TiO ₂ (15nm)) ² (d ₃ =0～2.4μm) film. value;

Figures 23a and 23b show the transmission and reflection colors and Lab values of the 100μm PDMS/(Al ₂ O ₃ (50nm)/Ag (10nm)/TiO ₂ (15nm)) ² film respectively.

Detailed ways

Embodiment 1. As shown in Figure 1, a color-controllable radiation cooling transparent window structure is specifically: 2μmSiO ₂ /glass/(50nmAl ₂ O ₃ /10nmAg/15nmTiO ₂ ) ² , both transmission and reflection are shown as Light yellow and light purple.

Embodiment 2. A color-controlled radiation refrigeration transparent window structure, specifically: 100 μm PDMS/glass/(50nmAl ₂ O ₃ /10nmAg/15nmTiO ₂ ) ^2. The mass ratio of PDMS to curing agent is: the ratio is 10:1. The curing agent is: methyltriethoxysilane (MTEOS).

Embodiment 3. A color-controlled radiation refrigeration transparent window structure, specifically: 2μmSiO ₂ /glass/(10nmAl ₂ O ₃ /10nmAg/5nmTiO ₂ ) ² appears light blue in transmission and yellow in reflection.

Embodiment 4. A color-controllable radiation refrigeration transparent window structure, specifically: 2μmSiO ₂ /glass/(20nmAl ₂ O ₃ /10nmAg/15nmTiO ₂ ) ^2. The transmission appears light yellow and the reflection appears light brown.

Embodiment 5. A color-controlled radiation refrigeration transparent window structure, specifically: 2μmSiO ₂ /glass/(30nmAl ₂ O ₃ /10nmAg/75nmTiO ₂ ) ² appears light red in transmission and light yellow in reflection.

Embodiment 6. A color-controllable radiation refrigeration transparent window structure, specifically: 2μmSiO ₂ /glass/(50nmAl ₂ O ₃ /10nmAg/55nmTiO ₂ ) ^2, which appears light orange in transmission and light blue in reflection.

Embodiment 7. A color-controlled radiation refrigeration transparent window structure, specifically: 2μmSiO ₂ /glass/(70nmAl ₂ O ₃ /10nmAg/75nmTiO ₂ ) ² appears blue in transmission and light yellow in reflection.

Embodiment 8. A color-controlled radiation refrigeration transparent window structure, specifically a structure of 2 μm SiO2/glass/(10nmAl2O3/10nmAg/55nmTiO2)2. Its transmission is yellow and its reflection is blue.

The film structure models described in Embodiments 1 to 8 can partially transmit VIS, reflect UV and NIR in summer, and emit heat to the outside through AW, and flip the windows in winter to prevent heat loss while absorbing outside heat into the inside. . The following part of this embodiment analyzes the transmission spectrum, reflection spectrum, and absorption spectrum lines of the film structure under different film thicknesses and period numbers, respectively elaborating on the performance in the UV, VIS, NIR, and MIR bands, and also lists the different film thicknesses. Combining the color and Lab value presented by reflection and transmission, select the color that is most comfortable for the human eye.

According to the GB/T2680-94 national standard, this article calculates the direct transmittance τ _e (Formula 4), direct reflectance ratio ρ _e (Formula 5) and direct absorption ratio α _e (Formula 6) of the film structure under the solar spectrum. and analyze its changing patterns. The lower τ _e , the better the shading effect of the film structure; the higher the ρ _e , the better the heat insulation effect; α _e represents the heat absorption capacity of the film structure, and a structure with a smaller α _e should be selected to reduce the film Impact on glass and the environment.

The actual cooling performance of the radiant cooling structure is affected by the radiant power of the sample surface, the absorbed power of atmospheric radiation at ambient temperature, the solar radiation power absorbed by the sample, and the power lost by non-radiative heat transfer. Formula (1) is the net cooling power of the sample surface .

P _net (T _s ,T _a )=P _rad (T _s )-P _atm (T _a )-P _sun -P _cond+conv (1)

In the formula, T represents the temperature in k, T _s is the sample surface temperature, T _a is the ambient temperature, P _rad is the radiation power on the sample surface, P _atm is the absorption power of atmospheric radiation, and P _sun is the solar energy absorbed by the sample. Radiation power, Pcond _+conv is the power lost by non-radiative heat transfer (that is, the heat lost by heat convection and heat conduction).

P _cond+conv = h _c (T _s -T _a ) (7)

In the formula, I _BB (T, λ) represents the radiance of the black body at temperature T, h is Planck's constant, c ₀ is the speed of light, k is Boltzmann's constant, and P _atm represents the atmospheric radiation of the black body at T _a The _absorption power _of Zenith angle, t(λ) is the atmospheric transmittance, P _sun has no angular integral, h _c is the non-radiative heat transfer coefficient, and the value of h _c is limited to 1.0~6.9W/m ² /K through thermal insulation. I _AM1.5 represents AM1.5 solar spectrum irradiance.

Kirchhoff's law of thermal radiation is used to describe the relationship between the emissivity and absorption ratio of an object. When studying radiation, the absorption ratio of the blackbody model generally used is equal to 1 (α=1), but the absorption ratio of the actual object is less than 1 (1>α>0). Kirchhoff's law of thermal radiation derives the relationship between the radiation emission and absorption ratio of actual objects. That is the formula In the formula, M is the radiation exit degree of the actual object, and M _b is the radiation exit degree of the black body at the same temperature. The emissivity ε is defined as the formula Therefore, α = ε, that is, the absorption curve of the coating structure is consistent with the emission curve. When a material is in thermal equilibrium, the absorption ratio of the material is always equal to the emissivity, otherwise the material itself cannot maintain thermal equilibrium. Equation (8) represents the surface average emissivity of the coating in the wavelength range of λ ₁ <λ < λ ₂ .

In the formula, ε (λ) represents the emissivity of the coating. I _BB (T, λ) represents the radiance of the black body at temperature T, h is Planck's constant, c ₀ is the speed of light, k is Boltzmann's constant, and P _atm represents the absorption of atmospheric radiation by the black body at T _a Power, α (λ, θ) is the absorptivity of the sample surface, ε _s (λ, θ) is the emissivity of the sample surface, ε _a (λ, θ) is the emissivity of the atmosphere, λ is the wavelength, θ is the zenith Angle, t (λ) is the atmospheric transmittance, P _sun has no angle integral, h _c is the non-radiative heat transfer coefficient, the value of h _c is limited to 1.0~6.9W/m ² /K through thermal insulation, I _{AM1 .5} represents AM1.5 solar spectrum irradiance.

In the formula: I _AM1.5 - relative spectral distribution of solar radiation; τ (λ) - transmittance of the sample in each band of sunlight; ρ (λ) - reflectance of the sample in each band of sunlight; α (λ) ——Absorption rate of sample in various wavelength bands of sunlight.

Use formulas (1) to (7) and formula (8) to calculate the surface net cooling power and surface average emissivity of the two structures respectively. Compare the net surface cooling power during the day and at night. The TFC software is used to calculate the impact of different incident angles and directions of sunlight on the spectral characteristics of the coating.

1. Construction and calculation of visible passive radiation cooling structural model

1.1. Construction and calculation of solar spectrum reflector model

The asymmetric periodic film structure used in the solar spectrum reflective layer can better integrate the excellent properties of multiple materials than the symmetrical film structure and is easier to achieve the desired effect. Figures 2a to 2c show the comparison of transmittance, reflectivity and absorptivity between asymmetric periodic structures and symmetric periodic structures in the 0.28μm to 2.5μm band.

In Figures 2a to 2c, the asymmetric structure is (Al ₂ O ₃ (50nm)/Ag (10nm)/TiO ₂ (15nm)) ² and the symmetrical structure is ITO (30nm)/Ag (15nm)/ITO (60nm)/Ag (15nm)/ITO (30nm) and TiO ₂ (25nm)/Ag (15nm)/TiO ₂ (50nm)/Ag (15nm)/TiO ₂ (25nm).

It can be seen from Figures 2a to 2c that in the ultraviolet light band, the (TiO ₂ /Ag/TiO ₂ ) ⁿ structure has the smallest transmittance, and the (Al ₂ O ₃ /Ag/TiO ₂ ) ⁿ structure has the largest reflectivity and the smallest absorption rate. In the visible light band, the (Al ₂ O ₃ /Ag/TiO ₂ ) ⁿ structure has the widest transmission band, with a center wavelength of 0.55 μm, and the transmittance at this time is 88.80%. In the near-infrared band, the (ITO/Ag/ITO) ⁿ structure has the highest reflectivity and the widest reflection band. The thickness of the Ag film layer has almost no effect on the resonance wavelength, so the wavelength and band width are mainly related to the dielectric film layer. The refractive index difference of the symmetrical structure dielectric film layer is 0, while there is a difference in the refractive index of the asymmetric film layer (at 0.55μm , the refractive index n of Al ₂ O ₃ is 1.68, and the refractive index n of TiO ₂ is 2.44), the greater the refractive index difference, the wider the transmission band.

In summary, the present invention adopts an asymmetric periodic structure, which is composed of an Al ₂ O ₃ /Ag (10nm) / TiO ₂ type solar spectrum reflective layer, a SiO ₂ or PDMS thermal infrared emitting layer and a base glass, as shown in Figure 1. The film thickness of Al ₂ O ₃ is specified as d ₁ , the film thickness of TiO ₂ is d ₂ , the film thickness of SiO ₂ is d ₃ , and the film thickness of PDMS is determined to be 100 μm. The influence of the ratio with the curing agent on the coating performance is mainly studied.

The reflective layer transmits visible light while reflecting UV and NIR. The emissive layer produces high emissivity in AW, achieving high transmittance of visible light, high reflectivity of ultraviolet and near-infrared, and high absorptivity of mid-infrared and thermal infrared. It has a film structure with anti- The multiple functions of ultraviolet light, high light transmittance, high heat insulation and heat dissipation reflect or emit the sunlight passing through the atmospheric window to achieve the purpose of passive radiation cooling.

In summer, sunlight is incident from the reflective layer. At this time, the window can reflect most of the heat and emit thermal infrared light to the outer layer. In winter, when the window is turned over, sunlight is incident from the infrared emitting layer, and the heat can be absorbed into the room.

The Ag film has high visible light transmittance and low infrared transmittance. In the present invention, 10 nm Ag is selected as the metal film layer. Al ₂ O ₃ thin films have excellent physical and chemical properties such as high transmittance, chemical stability, and high temperature resistance, so Al ₂ O ₃ is selected as the dielectric film. The TiO ₂ film is transparent in visible light, its high refractive index can reduce the reflection of the Ag film, and it has high chemical stability and mechanical hardness. For this reason, the TiO ₂ film is selected as another dielectric film ^[16] . Since the Ag film is easily oxidized and corroded and has poor adhesion, the Al ₂ O ₃ film layer is plated on the outermost side and the TiO ₂ film layer is plated on the innermost side. The base material is 1mm optical glass with a refractive index of 1.52.

1.2. Construction of thermal infrared emission layer

Raman AP and others used etching methods to change the microstructure of the SiO ₂ surface so that the SiO ₂ surface maintains high transmittance in the solar spectrum layer (0.2 μm ~ 3 μm), while the emissivity is close to 1 in the 5 μm ~ 30 μm band. The radiant cooling surface can achieve a stagnation temperature 4.9°C lower than the ambient temperature under solar irradiation conditions of 850W/ ^m2 , and when the surface temperature is equal to the ambient temperature, the net cooling power can reach 40.1W/ ^m2 . Polydimethylsiloxane (PDMS) is a silicone elastomer with high transmittance between 0.4μm and 1.8μm and good emissivity in atmospheric transparent windows. Therefore, both are chosen as thermal infrared emitting layers.

1.3. Calculation method of visible passive radiation cooling model

First, set the incident angle θ of sunlight to 0°, the incident center wavelength to 0.55 μm, the illumination light to be white, the attached medium and the removed medium to both be air, and set the sunlight to be incident from the emissive layer and emitted from the reflective layer. The effects of Al ₂ O ₃ film thickness, TiO ₂ film thickness and number of film layers on the optical properties, color and photothermal properties of the composite film in the solar spectrum range were calculated using TFCalc35 film system design software.

The reference value of the single layer film thickness of Al ₂ O ₃ and TiO ₂ is determined by the formula d=λ/4n (λ is the center wavelength of the incident light, n is the refractive index of the medium). The refractive index and extinction coefficient of Al ₂ O ₃ , Ag, and TiO ₂ were obtained from references. d ₁ =81.7236nm≈80nm, d ₂ =56.4496nm≈55nm. Assume _{d 3} = _{0 ,} calculate the _{structure and} (d ₁ ^Al ₂ O ₃ / _{Ag of} (10nm)/d ₂ TiO ₂ ) ² (d ₁ =80nm and d ₂ =5~75nm) transmittance, reflectivity, Absorbance spectral lines, and Lab colors for transmission and reflection. Lab color modes are composed of L, a and b respectively. L represents brightness, ranging from 0 to 100. 0 and 100 represent black and white respectively. As the L value increases, the brightness increases relatively; a represents the component from green to red, ranging from -128 to 128. -128 and +128 are green and red respectively. When a is 0, it is gray. b represents the component from blue to yellow, ranging from -128 to 128. When b is -128 and +128, they represent blue and yellow respectively. When b is 0, it means gray. As the b value increases, the chroma changes from blue to gray to yellow.

Calculate τ _e , ρ _e and α _e . Comparing the transmittance, reflectivity and absorptivity of the (Al ₂ O ₃ (50nm)/Ag (10nm)/TiO ₂ (15nm)) ⁿ structure under the solar spectrum layer when n is 1, 2 and 3, we seek to satisfy VIS The simplest structure with high transmittance, UV and NIR high reflectivity.

After determining the Al ₂ O ₃ /Ag(10nm)/TiO ₂ structure, the effect of SiO ₂ film thickness on AW emissivity and color was calculated. The refractive index and extinction coefficient of SiO ₂ were obtained from references. The thermal infrared wavelength range reaches the micron level. Calculate d ₃ SiO ₂ /(d ₁ Al ₂ O ₃ /Ag(10nm)/d ₂ TiO ₂ ) ² (d ₁ =50nm, d ₂ =15nm, d ₃ =0～2.4 μm) structure in the 0.28μm ~ 14μm band of transmittance, reflectivity, absorption spectral lines, as well as the Lab value under different film thickness, to obtain the impact of film thickness on transmission and reflection color. Then calculate τ _e , ρ _e , α _e and the average emissivity of the coating surface to verify the passive radiation cooling effect.

The SiO ₂ film was replaced with a PDMS coating with a thickness of 100 μm, and the refractive index and extinction coefficient of PDMS were obtained from reference ^[23] . Comparative calculation of the transmittance, reflectivity, and absorptivity in the 0.28 μm to 20 μm band when the ratio of the main reagent to the curing agent is 5:1, 10:1, 15:1, and 20:1, as well as the Lab values at different ratios . At the same time, calculate the average emissivity of τ _e , ρ _e , α _e and the structure surface at this time to test the passive radiation cooling effect.

According to formulas (1) to (7), set h _c =0, 1.0, 4.0 and 6.9W/m ² ·k, calculate the surface net cooling power of SiO ₂ and PDMS as emissive layers respectively, and obtain that when the ambient temperature and sample The net cooling power when the surface temperatures are equal, and the maximum and minimum temperature differences when the net cooling power is zero. Calculate the reflectivity, transmittance and absorptivity when the incident angle of sunlight is 0°, 15°, 30°, 45°, 60°, 75°, and 90°. At the same time, calculate the transmittance, reflectivity, absorptivity, and Lab value of sunlight incident from the emissive layer and the reflective layer, and compare the effects of windows in winter and summer.

2. Research on the structure and performance of solar spectrum visible reflective layer

2.1. Effect of Al ₂ O ₃ and TiO ₂ film thickness on the transmission performance of the solar spectrum visible reflective layer

Figure 3 shows that in the range of 0.28μm<λ<4μm, sunlight passes through the coating (d ₁ Al ₂ O ₃ /Ag (10nm)/d ₂ TiO ₂ ) ² (d ₁ =80nm and d ₂ =5~75nm) The transmittance of glass coated with composite thin film structure; Figure 4 shows the same wavelength band of sunlight passing through glass coated with (d ₁ Al ₂ O ₃ /Ag (10nm)/d ₂ TiO ₂ ) ² (d ₁ =10~80nm and d ₂ =55nm) transmittance of glass coated with composite thin film structure.

Figures 3 and 4 respectively show the regular effects of TiO ₂ and Al ₂ O ₃ film thickness on the transmittance of the solar spectrum layer. It can be seen from Figure 3 that when the Al ₂ O ₃ film thickness is fixed at 80 nm, as the TiO ₂ film thickness increases from 5 nm, the transmission peak red-shifts, the trough gradually deepens, and the visible light transmittance decreases. There are two transmission peaks at d ₂ =5nm and 15nm. The central wavelength of d ₂ =15nm is 0.55 μm; when d ₂ =25~55nm, a transmission peak appears in the ultraviolet band and red-shifts as the film thickness increases, d ₂ = There are three wave peaks at 65nm and 75nm, and the central wavelength is not in the visible light range. It can be concluded that as the TiO ₂ film thickness increases, the visible light transmittance will be greatly affected. To ensure the transmittance, the film thickness should be controlled within 55nm. It can be seen from Figure 4 that when the TiO ₂ film thickness is fixed at 55 nm, as the Al ₂ O ₃ film thickness increases from 10 nm, the transmission peak in this band shifts red and the transmission spectrum becomes wider. There are three transmission peaks when d ₁ =10 nm and d ₁ =20 nm, and there are two transmission peaks when d ₁ =30 to 80 nm. The smaller the film thickness, the closer the transmitted central wavelength is to 0.55μm. Comparing Figure 3-4, it can be seen that changes in TiO ₂ film thickness have a greater impact on transmittance.

Calculate from formula (9) that when d ₃ =0, the incident angle of sunlight is 0° and passes through the glass with (d ₁ Al ₂ O ₃ /Ag (10nm)/d ₂ TiO ₂ ) ² (d ₁ =10~80nm and d ₂ =5~75nm) film structure, the direct transmittance τ _e of each wavelength band of sunlight is as shown in Table 1 and Figure 5.

Table 1 (d ₁ Al ₂ O ₃ /Ag (10nm)/d ₂ TiO ₂ ) ² (d ₁ =10～80nm and d ₂ =5～75nm) composite film direct transmittance/%

To allow less heat to enter the room, a film thickness with a smaller direct transmission ratio should be selected. According to Table 1 and Figure 5, as d ₁ increases, τ _e shows an increasing trend, but when d ₂ =65nm and 75nm, τ _e first decreases and then increases, and the change range is small, within 1%. ; Taking d ₂ =35nm as the boundary, as d ₂ increases, the direct transmittance first increases and then decreases. When d ₂ <35nm, τ _e changes greatly. The lower τ _{e is} , the better the shading effect of the film structure is, so choose a film thickness combination with τ _e less than 50%.

The color of the film is obtained through TFcalc. Figure 20a shows the color of the transmission at this time. As the film thickness of Al ₂ O ₃ and TiO ₂ changes, the color of the film changes regularly. Figure 20a shows the transmission color table of the composite film of (d ₁ A _l2 O ₃ /Ag (10nm)/d ₂ TiO ₂ ) ² (d ₁ =10~80nm and d ₂ =5~75nm). It can be seen that, When d ₁ =10nm, 20nm, 30nm, d2 = 5nm, the color change trend is from blue to orange; when d ₁ =40nm, 50nm, the color changes from blue to orange to purple; d ₁ =60nm, 70nm, 80nm, When d ₂ =65nm and 75nm, the color changes from orange to blue; when d ₂ =15~55nm, it is orange with different brightness, and the change of d ₁ has little impact on the color. You should choose colors that are more comfortable for the human eye. Figure 20b shows the transmission color and Lab value corresponding to the film thickness used in the embodiment of the present invention.

Based on the transmittance curves, direct transmittance and color of transmission of different coating structures, the film thickness combinations shown in Table 2 are selected.

Table 2 (d ₁ Al ₂ O ₃ /Ag (10nm)/d ₂ TiO ₂ ) ² film thickness combinations that meet the transmission conditions

2.2 Effect of _{Al 2} O ₃ and TiO ₂ film thickness on the reflection performance of the visible reflective layer in the solar spectrum

Figure 6 shows that in the range of 0.28μm<λ<4μm, sunlight passes through a plate coated with (d ₁ Al ₂ O ₃ /Ag (10nm)/d ₂ TiO ₂ ) ² (d ₁ =80nm and d ₂ =5~75nm ) Reflectivity of glass with composite thin film structure; Figure 7 shows the sunlight passing through the glass coated with (d ₁ Al ₂ O ₃ /Ag (10nm)/d ₂ TiO ₂ ) ² (d ₁ =10~80nm and d ₂ in the same band) =55nm) reflectance of glass coated with composite thin film structure.

Figures 6 and 7 respectively show the regular effects of TiO ₂ and Al ₂ O ₃ film thickness on the reflectance of the solar spectrum layer. It can be seen from Figure 6 that when the Al ₂ O ₃ film thickness is fixed at 80 nm, as the TiO ₂ film thickness increases from 5 nm, the reflection peak red-shifts and the peak value gradually increases. In the near-ultraviolet band, the reflection spectral lines of d ₂ = 15 nm and 25 nm The band frequency is small, and the reflection peaks are at 55.84% and 66.52%; as the film thickness increases, the more peaks there are, the more unstable the reflectivity becomes; the visible light reflection peak increases, and the reflection spectrum broadens; the near-infrared reflectivity decreases, The reflection spectrum becomes narrower. Comprehensive results show that the TiO ₂ film thickness should be in the range of 5 to 35nm. It can be seen from Figure 7 that when the TiO ₂ film thickness is fixed at 55 nm, as the Al ₂ O ₃ film thickness increases from 10 nm, the reflection peak in this band shifts red and the reflection spectrum becomes wider. There is one reflection peak when d ₁ =10~40nm, and two reflection peaks when d ₁ =50~80nm; the near-infrared reflectivity decreases and the reflection spectrum becomes narrower. Comparing Figures 6-7, it can be seen that changes in TiO ₂ film thickness have a greater impact on reflectivity.

Calculate from formula (10) that when d ₃ =0, the incident angle of sunlight is 0° and passes through the glass with (d ₁ Al ₂ O ₃ /Ag (10nm)/d ₂ TiO ₂ ) ² (d ₁ =10~80nm and d ₂ =5~75nm) film structure, the direct reflectance ρ _e of each wavelength band of sunlight is shown in Table 3 and Figure 8.

Table 3 (d ₁ Al ₂ O ₃ /Ag (10nm)/d ₂ TiO ₂ ) ² (d ₁ =10～80nm and d ₂ =5～75nm) composite film direct reflectance/%

In order to allow less heat to enter the room, the film thickness should be selected when the direct reflection ratio is large. According to Table 3 and Figure 8, it can be seen that as d ₁ increases, the direct reflectance shows a decreasing trend, but when d ₂ =75nm, ρ _e first increases and then decreases, and the change range is small, within 1%; d ₂ =35nm is the boundary. As d ₂ increases, the direct reflection ratio first decreases and then increases. When d ₂ <35nm, ρ _e changes greatly. The higher ρ _e is, the better the thermal insulation effect is, so choose a film thickness combination with ρ _e greater than 40%.

The table given in Figure 21a shows the color of the reflection at this time. As the film thickness of Al ₂ O ₃ and TiO ₂ changes, the color of the film changes regularly. Figure 21a shows the reflection color of the composite film of (d ₁ A _l2 O ₃ /Ag (10nm)/d ₂ TiO ₂ ) ² (d ₁ =10~80nm and d ₂ =5~75nm). Figure 21b shows the reflection color and Lab value corresponding to the partial film thickness used in the embodiment of the present invention.

It can be seen from Figure 21a that changes in d ₁ and d ₂ have a greater impact on the reflection color of the film. You should choose a film thickness combination that is more comfortable for human eyes to observe, such as d ₁ =25nm, d ₂ =20nm; do not choose a color that is too dark, such as d ₁ =35nm, d ₂ =50nm.

The film thickness combinations selected based on the above conditions are shown in Table 4.

Table 4 (d ₁ Al ₂ O ₃ /Ag (10nm)/d ₂ TiO ₂ ) ² film thickness combinations that meet the reflection conditions

2.3 Effect of _{Al 2} O ₃ and TiO ₂ film thickness on the absorption performance of the visible reflective layer in the solar spectrum

Figure 9 shows that in the wavelength range of 0.28μm<λ<4μm, sunlight passes through a plate coated with (d ₁ Al ₂ O ₃ /Ag (10nm)/d ₂ TiO ₂ ) ² (d ₁ = 80nm and d ₂ = 5~ 75nm) composite film structure coated glass; Figure 10 shows the same band of sunlight passing through the glass coated with (d ₁ Al ₂ O ₃ /Ag (10nm)/d ₂ TiO ₂ ) ² (d ₁ =10 ~ 80nm and d ₂ =55nm) The absorptivity of glass coated with composite thin film structure.

Figures 9 and 10 respectively show the regular effects of TiO ₂ and Al ₂ O ₃ film thickness on the absorption rate of the solar spectrum layer. The absorption peaks are mainly concentrated in the near-ultraviolet band. In Figure 9, as the TiO ₂ film thickness increases, the absorption peak gradually increases and red-shifts. It can be seen from Figure 10 that the near-ultraviolet absorption rate is low when d ₁ =60~80nm; in the near-infrared band, the absorption rate increases as the film thickness increases.

Calculate from formula (11) that when d ₃ =0, the incident angle of sunlight is 0° and passes through the glass with (d ₁ Al ₂ O ₃ /Ag (10nm)/d ₂ TiO ₂ ) ² (d ₁ =10~80nm and d ₂ =5~75nm) film structure, the direct absorption ratio α _e of each wavelength band of sunlight is shown in Table 5 and Figure 11.

Table 5 (d ₁ Al ₂ O ₃ /Ag (10nm)/d ₂ TiO ₂ ) ² (d ₁ =10～80nm and d ₂ =5～75nm) composite film direct absorption ratio/%

In order to prevent the passive radiation refrigeration coating itself from absorbing too much heat, which would lead to an increase in non-radiative heat transfer, a film thickness combination with a smaller α _e should be selected. It can be seen from Table 5 and Figure 11 that as d ₁ increases, the direct absorption ratio increases; taking d ₂ =45nm as the boundary, as d ₂ increases, the direct absorption ratio first decreases and then increases. When d ₂ <25nm, α _e changes greatly.

In summary, based on the analysis of the coating’s transmittance, reflectance and absorptivity spectral lines in the solar spectrum layer, photothermal performance and color of transmission and reflection, five groups of film thicknesses can be screened as shown in Table 6. Figures 12a to 12c show the transmittance, reflectance, and absorptivity of the five groups.

Table 6 screens five groups of film thicknesses

It can be seen from Figures 12a to 12c that the ones with better near-ultraviolet reflection effect are group 1 and group 2, the ones with lower absorption rate are group 2, group 3 and group 4; the ones with high visible light transmittance are group 1, group 2, group 3 and group 4; near infrared The ones with higher reflectivity are group 1, group 2, group 3, and group 4. In summary, the two groups of film thicknesses are optimal, namely d ₁ =50nm and d ₂ =15nm. At this time, the near-ultraviolet reflection peak of the window is 45.11%, the visible light transmittance is about 80%, the near-infrared reflectivity is about 90%, τ _e is 49.11%, ρ _e is 42.87%, and α _e is 8.02 %, the transmission and reflection show light yellow and light purple acceptable to the human eye.

3. The influence of periodic structure on the spectral performance of the visible reflective layer in the solar spectrum

Analyze the transmittance, reflectance and absorptivity of (Al ₂ O ₃ (50nm)/Ag (10nm)/TiO ₂ (15nm)) ⁿ film system structure in the solar spectrum range when n is 1, 2 and 3 respectively. , Figure 13a-13c.

It can be seen from Figure 13a-13c that when n=1, the visible light transmittance is the highest, with a peak value of 90.55%, and the ultraviolet light absorption rate is the lowest, but the reflectivity in the ultraviolet and near-infrared bands is low; when n=3, the visible light transmittance is relatively low, and the center The wavelength is at 0.47nm and 0.62nm, and the absorption rate is higher in the 0.28μm<λ<1μm band. The absorption peak is 15.27%, but the ultraviolet and near-infrared reflectivity are the highest. The ultraviolet reflection peak is 49.75%; transmittance and reflection when n=2 The rate and absorption rate are both medium. The central wavelength of the transmittance in the visible light band is 0.55nm, and the reflection peak in the ultraviolet light band is 43.87%.

In summary, the dual structure has good visible light transmission effect, and the reflection effect in the ultraviolet and near-infrared bands can also meet expectations, and the absorption rate in the ultraviolet band is not high, so the reflective layer structure is determined as (Al ₂ O ₃ (50nm )/Ag(10nm)/TiO ₂ (15nm)) ² .

4. The influence of the structure of the thermal infrared emitting layer on its spectral performance

After the reflection structure on the back of the base glass is determined, an emissive layer is coated on top of the base glass, that is, a SiO ₂ film or a PDMS film with a high absorption rate in the thermal infrared band. The SiO ₂ film thickness and PDMS solvent ratio are analyzed respectively to determine the transmittance. , reflectivity and absorptivity spectral lines, photothermal properties, average emissivity of the coating surface, and the influence of the color of transmission and reflection to obtain the optimal film thickness of SiO ₂ and the optimal ratio of the PDMS solvent. Finally, the passive radiation cooling effects of the two are compared and the applicable situations are analyzed.

4.1. Effect of SiO ₂ thermal infrared emitting layer on spectral performance

Use _SiO2 as the emissive layer. Figures 14a-14c show that in the range of 0.28μm<λ<14μm, d ₃ SiO ₂ /(Al ₂ O ₃ (50nm)/Ag (10nm)/TiO ₂ (15nm)) ² (d ₃ =0～2.4 μm) of the transmittance, reflectance, and absorptivity of the composite thin film structure.

It can be seen from Figure 14a-14c that when d ₃ =0.1 μm, the visible light transmission peak is the highest at 89.60%; every 0.4 μm increase in SiO ₂ film thickness from 0 will reduce the visible light transmittance by about 1.5%; the ultraviolet light transmittance will be reduced by about 4%. Band reflectivity; increase UV light absorption by about 2%. The reflectivity in the near-infrared band gradually appears with two reflection peaks, and the reflection spectrum becomes narrower and narrower. The absorption peaks in the thermal infrared band are getting higher and higher. MIR has two absorption peaks when d ₃ =0.1 μm and 0.4 μm, and three absorption peaks when d ₃ =0.8~2.4 μm. In the wavelength range of 8 μm < λ < 14 μm, the absorption rate does not change significantly when the film thickness is greater than 2 μm. When d ₃ = 2 μm, the absorption peaks are 66.34%, 76.23% and 53.71% respectively.

Calculate from formula (9-11) that the incident angle of sunlight is 0° and passes through d ₃ SiO ₂ /glass/(Al ₂ O ₃ (50nm)/Ag (10nm)/TiO ₂ (15nm)) ² (d ₃ = The direct transmittance, direct reflectance and direct absorption ratio of the film structure (0~2.4μm) are as shown in Table 7 and Figure 15.

Table 7 Effect of SiO ₂ film thickness on photothermal performance of composite thin film structure of d ₃ SiO ₂ /(Al ₂ O ₃ (50nm)/Ag (10nm)/TiO ₂ (15nm)) ² (d ₃ =0～2.4μm) Influence/%

SiO ₂ film thickness/μm 0 0.1 0.4 0.8 1.2 1.6 2.0 2.4 direct transmittance 49.11 49.40 48.51 47.67 46.83 46.00 45.20 44.41 direct reflectance 42.87 42.22 42.14 41.69 41.26 40.84 40.44 40.05 direct absorption ratio 8.02 8.42 9.39 10.69 11.95 13.19 14.40 15.58

Table 7 and Figure 15 characterize the effect of SiO ₂ film thickness on the photothermal performance of the coating structure in the range of the solar spectrum (0.28μm<λ<4μm). When the SiO ₂ film thickness is 0.1 μm, the direct transmittance is 0.29% higher than that without SiO ₂ coating, that is, 2.9 W more heat is transmitted per square meter; when the SiO ₂ film thickness is greater than 0.1 μm, the direct transmittance varies with the film thickness. As it increases and decreases, the shading coefficient increases. The direct reflectance decreases as the _SiO2 film thickness increases. The direct absorption ratio increases as the SiO ₂ film thickness increases. If the direct absorption ratio is too large, the non-radiative heat transfer power of the coating structure itself will increase, resulting in a weakened radiative cooling effect.

The average emissivity of the coating surface in the thermal infrared band (8μm<λ<13μm) is calculated through formula (8), as shown in Table 8.

Table 8 (Al ₂ O ₃ /Ag (10nm)/TiO ₂ ) ² (d ₃ =0～2.4μm) composite film surface average emissivity/%

d ₃ /μm 0 0.1 0.4 0.8 1.2 1.6 2 2.4 Emissivity/% 4.19 16.55 28.69 34.82 40.09 45.14 49.21 52.55

It can be seen from Table 8 that SiO ₂ can significantly increase the average emissivity of the surface of the glass. As the SiO ₂ film thickness increases, the average emissivity of the coating surface increases, but the magnitude of the increase decreases. The greater the surface average emissivity in the thermal infrared band, the more heat is emitted to the outside world, and the better the passive radiation cooling effect is.

The film color is obtained through TFcalc. Figure 22a and Figure 22b are respectively the composite of d ₃ SiO ₂ /(Al ₂ O ₃ (50nm)/Ag (10nm)/TiO ₂ (15nm)) ² (d ₃ =0～2.4μm) The transmission color and reflection color presented by the film and the corresponding Lab values. It is found from Figure 22a and Figure 22b that changes in the thickness of the SiO ₂ film have little effect on the color, and the brightness difference changes very little. When the SiO ₂ film thickness changes by 0.4 μm, no obvious color difference that can be recognized by the human eye occurs. The difference in brightness of transmission is large, but the difference of brightness of reflection is small.

In summary, a _SiO2 film with a film thickness of 2 μm is selected to be plated on the substrate to absorb heat and dissipate it to the outside, thus preventing heat from entering the room. At this time, the reflection peak of the window in near ultraviolet is 27.11%, the transmittance of visible light is above 66.70%, the reflectance of near infrared is about 94.75%, the average surface emissivity of thermal infrared is 49.21%, and τ _e is 45.20% , ρ _e is 40.44%, α _e is 14.40%, and the transmission and reflection are light yellow and light purple acceptable to the human eye.

4.2. Effect of PDMS thermal infrared emitting layer on spectral performance

Use PDMS as the emissive layer. Figures 16a-16c show the comparison of 100μm PDMS/(Al ₂ O ₃ The transmittance, reflectance and absorptivity of the composite thin film structure of (50nm)/Ag(10nm)/TiO ₂ (15nm)) ² .

It can be seen from Figures 16a-16c that the ratio of the main reagent to the curing agent has little effect on the transmittance, and the transmittance in the visible light range remains above 42%; at 0.54 μm, the transmittance of 10:1 is the highest, which is 90.77%. 20:1 has the lowest transmittance of 88.44%. The impact on reflectivity is mainly concentrated at 6~8μm, the reflection peak in the near-ultraviolet band is 42.28%, and the reflectivity in the near-infrared band remains above 82%; at 3.3~3.5μm, there are defects in reflectivity, but at this time the solar spectrum Irradiance and blackbody radiation are both approximately equal to 0, and have little impact on reflectance and emission power. The impact on the absorptivity is also concentrated at 6 to 8 μm. The absorptivity at 10:1 is overall high, and the absorption peak at 6.2 μm is 75.98%; the absorption spectrum in the thermal infrared band is very broad.

Calculate from formulas (9) to (11) when the incident angle of sunlight is 0° and passes through the film structure of 100μm PDMS/glass/(Al ₂ O ₃ (50nm)/Ag (10nm)/TiO ₂ (15nm)) ² The direct transmittance, direct reflectance and direct absorption ratio, as shown in Table 9 and Figure 17.

Table 9 Effect of PDMS solvent ratio on photothermal performance of 100μm/(Al ₂ O ₃ (50nm)/Ag (10nm)/TiO ₂ (15nm)) ² composite film structure/%

Table 9 and Figure 17 characterize the effect of the ratio of PDMS to curing agent on the photothermal performance of the coating structure within the solar spectrum range. The ratio of main reagent to curing agent has little effect on the solar thermal coefficient. With PDMS coating, the direct transmittance is about 0.5% higher, that is, 5W more heat is transmitted per square meter; the direct reflection ratio is about 1.5% lower, that is, 15W less heat is reflected per square meter; the direct absorption ratio is increased by about 1%, that is, every square meter Mido absorbs 10W of heat.

The average emissivity of the coating surface in the thermal infrared band (8μm<λ<13μm) is calculated through formula (8), as shown in Table 10.

Table 10 Composite film emissivity/% of PDMS/(Al ₂ O ₃ /Ag(10nm)/TiO ₂ ) ²

As can be seen from Table 10, PDMS can increase the average emissivity of the surface of the window by more than 90%, but the ratio of the main reagent to the curing agent has little effect on the average emissivity of the coating surface, and the fluctuation amplitude is maintained within 0.1%. The greater the surface average emissivity in the thermal infrared band, the more heat is emitted to the outside world, and the better the passive radiation cooling effect.

The film color is obtained through TFcalc. Figure 23a and Figure 23b are respectively the reflection color and transmission color of the 100μm PDMS/(Al ₂ O ₃ (50nm)/Ag (10nm)/TiO ₂ (15nm)) ² composite film and the corresponding Lab value.

It can be seen from Figures 23a and 23b that as the ratio of PDMS to curing agent changes, the color displayed by the transmission basically does not change, and the Lab value changes within 0.7; the reflection color shows a change that can be recognized by the naked eye, 5:1 and 15: At 1, the reflection color is darker and the brightness is smaller. At 10:1 and 20:1, the reflection color is lighter and the brightness is larger.

In summary, a PDMS film with a ratio of 10:1 is selected to be plated on the substrate to absorb heat and dissipate it to the outside, thereby preventing heat from entering the room. At this time, the near-ultraviolet reflection peak of the window is 42.28%; the visible light transmittance is above 42%, and the central wavelength of the transmittance is 0.54 μm; the near-infrared reflectivity is above 82%, and the average surface emissivity of thermal infrared is 94.54%, τ _e is 49.56%, ρ _e is 41.51%, α _e is 8.96%, and the transmission and reflection are light yellow and light pink acceptable to the human eye.

5 Analysis of factors affecting radiation cooling power

According to formulas (1) to (7), assuming that the ambient temperature _Ta = 300K, h _c = 0, 1.0, 4.0 and 6.9W/m ² ·k, calculate respectively when SiO ₂ and PDMS are used as emissive layers, day and night The net cooling power of the window surface and a comparative analysis of daytime and nighttime power.

5.1 Analysis of factors affecting radiation cooling power when SiO ₂ is used as the emissive layer

The net cooling power on the surface of SiO ₂ (2μm)/(Al ₂ O ₃ (50nm)/Ag (10nm)/TiO ₂ (15nm)) ² composite film during the day and night is shown in Figure 18a-18b.

It can be seen from Figure 18a that when SiO ₂ is used as the emissive layer, the relationship between the net cooling power of the coating surface and the temperature difference during the daytime. When T _s <T _a , the smaller h _c is, the higher the cooling power is. When T _s = _Ta , ΔT = 0, the net cooling power P _net of the sample surface is -85.92W/m ² . When T _s >T _a , the smaller h _c is, the lower the cooling power is. As ΔT increases, P _net reaches zero. At this time, ΔT _min =10.0k (h _c =6.9W/m ² ); ΔT _max = 46.7k (h _c =0).

Figure 18b shows that the changes during the day and night are consistent. When T _s <T _a , the net cooling power reaches zero. At this time, ΔT _max =-7.0k (h _c =6.9W/m ² ); ΔT _min =-53.9k (h _c =0). When T _s = _Ta , ΔT =0, P _net =58.08W/m ² .

To sum up, considering all heat exchanges, at thermal equilibrium, the maximum temperature increase during the day is 46.7°C, and the minimum temperature drop at night is 7.0°C. Since the solar radiation power absorbed at night is zero, the net cooling power at night is higher than during the day. Height 144W/m ² .

5.2 Analysis of factors affecting radiation cooling power when PDMS is used as the emissive layer

The surface cooling power of PDMS (100μm)/(Al ₂ O ₃ (50nm)/Ag (10nm)/TiO ₂ (15nm)) ² composite film samples during the day and night is shown in Figures 19a to 19b. It can be seen from Figures 19a to 19b that the net cooling power changes in the same way when SiO ₂ and PDMS are used as emissive layers. When T _s <T _a , the smaller h _c is, the higher the cooling power is; as T _s decreases, the net cooling power reaches zero. When h _c = 6.9W/m ² , the slope of P _net is the largest during the day. ΔT _max =-3.3k, ΔT _max =-11.3k at night; when h _c =0, ΔT _min =-9.3k during the day, and ΔT _min =-33.7k at night and during the day. When T _s = _Ta , ΔT = 0, P _net = 36.93W/m ² during the day, and P _net = 123.56 W/m ² at night. When T _s >T _a , the smaller h _c is, the lower the cooling power is.

To sum up, considering all heat exchanges, at thermal equilibrium, the minimum temperature drop during the day is 3.3°C, and the minimum temperature drop at night is 11.3°C. Since the solar radiation power absorbed at night is zero, the net cooling power at night is higher than during the day. 89.63W/m ² .

The final conclusion is that: when using 2μmSiO ₂ /glass/(50nmAl ₂ O ₃ /10nmAg/15nmTiO ₂ ) ² and PDMS(100μm)/glass/(Al ₂ O ₃ /Ag(10nm)/TiO ₂ ) ² structures , both can achieve the passive radiation cooling effect, and use the rotating shaft to flip the glass to achieve near-ultraviolet high reflection and thermal infrared high reflection effects. In summer, sunlight is incident from the reflective layer, and under the action of the film structure, only visible light enters the room, while indoor thermal infrared light is also emitted to the outside world, achieving the effect of isolating outdoor heat and indoor heat dissipation. In winter, sunlight is incident from the emitting layer, and most of the visible light and near-infrared heat enters the room. At the same time, the heat is emitted into the room through its absorption effect, and the indoor heat is reflected back into the room to achieve a warm and insulating effect. PDMS as the emissive layer is more suitable for areas with higher ambient temperatures, and SiO ₂ as the emissive layer is more suitable for areas with low ambient temperatures. Comparison of the structural performance of the two groups is shown in Table 11.

Table 11 Comparison of structural performance of the two groups

Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention, but not to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that: The technical solutions described in the foregoing embodiments can still be modified, or some or all of the technical features can be equivalently replaced; and these modifications or substitutions do not deviate from the essence of the corresponding technical solutions from the technical solutions of the embodiments of the present invention. scope.

Claims (8)

1. A color-controllable radiation refrigeration transparent window structure, characterized in that: comprises a glass layer, wherein one side surface of the glass layer is a solar spectrum reflecting layer, the other side surface is a thermal infrared emitting layer, and the solar spectrum reflecting layer is (Al ₂ O ₃ /Ag(10nm)/TiO ₂ ) ⁿ The thermal infrared emission layer is SiO ₂ Or PDMS.

2. The color-controllable radiation-cooled transparent window structure of claim 1, wherein: al in the solar spectrum reflecting layer ₂ O ₃ 10-80nm, 10nm for Ag and 10nm for TiO ₂ Selecting 5-75nm.

3. The color-controllable radiation-cooled transparent window structure of claim 2, wherein: al in the solar spectrum reflecting layer ₂ O ₃ 50nm, 10nm for Ag and 10nm for TiO ₂ 15nm was chosen.

4. The color-controllable radiation-cooled transparent window structure of claim 1, wherein: thermal infrared emission layer SiO ₂ 0.1-2.4 μm.

5. The color controllable radiation chilled transparent window structure of claim 4, wherein: thermal infrared emission layer SiO ₂ Is 2 μm.

6. The color-controllable radiation-cooled transparent window structure of claim 1, wherein: the thermal infrared emission layer PDMS was 100 μm.

7. A color controllable radiation chilled transparent window structure according to claim 1 or 2 or 3, wherein: n takes a value of 1-3.

8. A color controllable radiation chilled transparent window structure according to claim 1 or 2 or 3, wherein: n takes on a value of 2.