Composite Cooling Film With Antisoiling Layer for Daytime Radiative Cooling
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Solution Overview
Problem
Current passive radiative cooling technologies face challenges in effectively cooling substrates, such as vehicles and buildings, during the daytime due to high solar radiation, which interferes with radiative cooling mechanisms, and there is a need for materials that balance reflectivity across various wavelengths to enhance cooling performance.
Innovation Solution
A composite cooling film comprising a reflective microporous layer with a fluoropolymer and an antisoiling layer, which is diffusely reflective across a broad wavelength range (400-2500 nanometers) and has a high absorbance in the atmospheric window (8-13 microns), combined with an optional infrared-reflective layer to manage thermal radiation, ensuring efficient cooling both day and night.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If a passive radiative cooling film is used to cool substrates during daytime, then radiative cooling through the atmospheric window is achieved, but high solar radiation interferes with the cooling mechanism
Solution Approach 1:
The cooling film is divided into multiple functional layers: a solar reflective layer that segments and reflects solar radiation (0.3-2.5 microns), an infrared emissive layer that segments the thermal radiation spectrum to emit through the atmospheric window (8-13 microns), and a substrate layer. This segmentation allows independent optimization of solar reflection and infrared emission properties.
Solution Approach 2:
Different layers of the film have specialized local properties: the solar reflective layer has high reflectance specifically for solar wavelengths, while the infrared emissive layer has high emittance specifically for atmospheric window wavelengths. This local quality optimization ensures that each layer performs its specific function efficiently without compromising the other.
2Temperature
If high reflectivity is achieved across solar wavelengths to reduce solar heating, then cooling performance during daytime improves, but the complexity of the film structure increases
Solution Approach 1:
The film uses composite material structures where the solar reflective layer and infrared emissive layer are combined in a single integrated film. This composite approach achieves both solar reflection and infrared emission properties that would be difficult to obtain with single materials, while maintaining a manageable multi-layer structure.
Solution Approach 2:
The film achieves different optical properties by changing material parameters and layer thicknesses. The solar reflective layer uses materials with high reflectance in the 0.3-2.5 micron range, while the infrared emissive layer uses materials with high emittance in the 8-13 micron range. By adjusting layer thicknesses and material compositions, the film optimizes both solar reflection and infrared emission without excessive complexity.
3Loss of energy
If high emittance is achieved in the atmospheric window (8-13 microns) to enhance radiative cooling, then heat elimination improves, but solar absorbance may increase
Solution Approach 1:
The film segments the electromagnetic spectrum into distinct wavelength ranges handled by different layers. The solar reflective layer handles the 0.3-2.5 micron solar range with high reflection, while the infrared emissive layer handles the 8-13 micron atmospheric window with high emission. This spectral segmentation ensures that high infrared emittance does not compromise solar reflectance.
Solution Approach 2:
Each layer has optimized local optical properties for its specific wavelength range. The solar reflective layer is designed with high reflectance specifically for solar wavelengths, while the infrared emissive layer is designed with high emittance specifically for atmospheric window wavelengths. This local quality optimization resolves the contradiction between solar absorbance and infrared emission.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The composite cooling film effectively reflects solar radiation during the day and radiates heat through the atmospheric window at night, maintaining a lower temperature than ambient, thus providing enhanced thermal management for substrates.
Implementation Method 1
the reflective microporous layer comprises a first fluoropolymer and is diffusely reflective of electromagnetic radiation over a majority of wavelengths in the range of 400 to 2500 nanometers
Implementation Method 2
passive cooling mechanism for a terrestrial body at ambient temperature by eliminating heat via radiative emission through the atmospheric window
Implementation Method 3
The Earth's atmosphere has a semi-transparent window in the infrared wavelength range between 8 and 13 microns, i.e., the atmosphere's radiative emission is very weak in that window
Implementation Method 4
an antisoiling layer secured to a first major surface of a reflective microporous layer, wherein the antisoiling layer has an outwardly facing antisoiling surface opposite the reflective microporous layer
Data Source
Figure 1
Figure 2A
Figure 2B~2C
AI summary
A composite cooling film (100) comprises an antisoiling layer (160) secured to a first major surface of a reflective microporous layer (110). The reflective microporous layer (110) comprises a first fluoropolymer and is diffusely reflective of electromagnetic radiation over a majority of wavelengths in the range of 400 to 2500 nanometers. The antisoiling layer (160) has an outwardly facing antisoiling surface (162) opposite the micro-voided polymer film. An article (1100) comprising the composite cooling film (1112) secured to a substrate (1110) is also disclosed.