Chromatic radiative cooling device
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Solution Overview
Problem
Conventional radiative cooling devices struggle to simultaneously achieve high reflection of sunlight and efficient heat emission in the atmospheric window while implementing various colors, leading to temperature increases due to sunlight absorption.
Innovation Solution
A color-developing radiative cooling device incorporating a liquid crystal layer with cholesteric liquid crystal, a reactive mesogen compound, and a chiral dopant, along with additional layers such as a protective film, reflective, substrate, and transmissive layers, to control light reflection and emission across different wavelength ranges.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If conventional radiative cooling devices use metals to reflect specific wavelengths of sunlight, then color expression is achieved, but the devices absorb remaining wavelengths and temperature increases
Solution Approach 1:
The patent employs a composite structure consisting of a metal layer for selective sunlight reflection and color expression, combined with a dielectric layer having high emissivity in the atmospheric window region (8-13 μm). This composite material approach allows simultaneous achievement of color expression through metal reflection and efficient heat emission through the dielectric layer, preventing temperature increase despite sunlight absorption.
2Temperature
If radiative cooling devices maximize sunlight reflection to achieve cooling, then cooling performance improves, but color expression becomes limited
Solution Approach 1:
The patent segments the spectral control function into two distinct layers: the metal layer handles visible light reflection for color expression, while the dielectric layer handles infrared emission for cooling performance. This segmentation allows each layer to optimize its specific function without compromising the other, achieving both vivid colors and effective radiative cooling.
3Illumination intensity
If conventional devices absorb sunlight to achieve color, then color expression is achieved, but cooling performance deteriorates
Solution Approach 1:
The dielectric layer acts as an intermediary that enables efficient heat emission in the atmospheric window region (8-13 μm). This intermediary layer compensates for any sunlight absorption by providing a dedicated pathway for thermal radiation to escape to space, thereby maintaining cooling performance even when color expression requires some light absorption.
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 device achieves excellent cooling performance by reflecting sunlight and emitting heat in the atmospheric window, while allowing for vivid color expression and maintaining temperatures lower than the ambient temperature.
Implementation Method 1
control the absorption, reflection, and emission of light independently in each wavelength range
Implementation Method 2
a liquid crystal layer including a cholesteric liquid crystal, the cholesteric liquid crystal including a reactive mesogen compound and a chiral dopant
Implementation Method 3
emit heat well into space by having high absorptivity or emissivity in the long-wavelength infrared region
Implementation Method 4
the atmospheric window region is about 8-13 μm. Therefore, in order to maximize the heat emission capability of a passive cooling device, the absorptivity or emissivity in the 8-13 μm range should be at its maximum
Implementation Method 5
control the absorption, reflection, and emission of light independently in each wavelength range
Data Source
AI summary
The present invention relates to a color-developing radiative cooling device including a liquid crystal layer containing a cholesteric liquid crystal having a pitch range of 50 nm to 550 nm, wherein the cholesteric liquid crystal includes a reactive mesogen compound and a chiral dopant, thereby implementing various colors while maintaining excellent cooling performance.