Structures for passive radiative cooling
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Solution Overview
Problem
Current radiative cooling technologies are not practical for commercial applications due to high costs, lack of flexibility, and inefficiencies in outdoor environments, particularly in refrigerated trucking, where significant energy and emissions are wasted due to conventional cooling methods.
Innovation Solution
Development of a flexible, transparent passive radiative cooling structure that absorbs and emits infrared radiation at wavelengths where the Earth's atmosphere is transparent, using embedded particles with diameters greater than 30 μm and a thermoplastic polymer base, allowing for efficient cooling of surfaces while maintaining visibility and durability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If non-polymer particles are embedded randomly in a polymeric matrix to achieve radiative cooling, then cooling capacity is improved, but light scattering increases and transparency is lost
Solution Approach 1:
The patent changes the particle size parameter to greater than 30 μm and controls the volume percentage between 2% and 25%, which optimizes the balance between radiative cooling capacity and light scattering. This parameter optimization allows the composite material to maintain visible light transparency while achieving effective cooling in the 7-13 μm atmospheric window.
Solution Approach 2:
The patent creates a composite material system consisting of non-polymer particles embedded in a polymeric matrix. This composite structure combines the radiative cooling properties of the particles with the flexibility and processability of the polymer, achieving both cooling capacity and transparency when properly formulated.
2Temperature
If conventional cooling methods are used in refrigerated trucking, then cooling effectiveness is maintained, but energy consumption and emissions increase significantly
Solution Approach 1:
The radiative cooling structure provides self-cooling capability by passively emitting thermal radiation through the atmospheric window without requiring external energy input. The structure automatically dissipates heat to the cold sink of space, eliminating the need for energy-consuming refrigeration systems in applications like refrigerated trucking.
Solution Approach 2:
The patent replaces active mechanical cooling systems with passive radiative cooling. Instead of using energy-intensive compressors and refrigerants, the system uses the natural radiative heat transfer mechanism to achieve cooling, substituting a mechanical system with a passive physical phenomenon.
3Illumination intensity
If radiative cooling structures are made with small particle sizes, then transparency is improved, but cooling capacity in the atmospheric window decreases
Solution Approach 1:
The patent identifies and optimizes the critical particle size parameter at greater than 30 μm, which is larger than conventional approaches. This parameter change enables the particles to effectively interact with infrared radiation in the atmospheric window while minimizing visible light scattering, thereby achieving both transparency and cooling capacity simultaneously.
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 solution provides a cost-effective, flexible, and efficient cooling method that reduces energy consumption and emissions by effectively dissipating heat through the atmosphere's transparency window, enhancing the efficiency of various applications including solar panels, refrigerated containers, and reducing fuel usage in trucking.
Implementation Method 1
passive radiative cooling is achieved by the use of devices that emit wavelengths corresponding to the transparency windows in the Earth's atmosphere... thermal radiation emitted in these wavelengths from an object on the surface of the Earth will be transferred to the cold sink of space
Implementation Method 2
there is a so-called 'atmospheric window' at IR radiation wavelengths between about 7 μm to 13 μm where radiation emitted from the Earth's surface leaves the atmosphere
Implementation Method 3
passive emissive cooling can be used to reduce the temperature of an object, even at the surface of the planet... Radiative cooling has been demonstrated under both nighttime daytime conditions
Data Source
AI summary
Passive radiative cooling structures and apparatus manufactured with such cooling structures conserve energy needs. A flexible film transparent to visible light incorporates particles at a volume percentage larger than 25% so as to absorb and emit infrared radiation at wavelengths where Earth's atmosphere is transparent. Another film transparent to visible light is thin and flexible and configured to absorb and emit infrared radiation at wavelengths where Earth's atmosphere is transparent, wherein etchings or depositions are present on one or both surfaces. A high efficiency cooling structure has an emissive layer sandwiched between a waveguide layer and a thermal conductive layer. A solar cell panel is covered by a transparent passive radiative cooling film. A container housing an active cooling unit incorporates passive radiative cooling structures on one or more exterior surfaces.