Ideal spectral emissivity for radiative cooling of earthbound objects

Suwan Jeon,Jonghwa Shin

doi:10.1038/s41598-020-70105-y

Suwan Jeon, Jonghwa Shin

Open Access

https://doi.org/10.1038/s41598-020-70105-y

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Abstract

We investigate the fundamental limit of radiative cooling of objects on the Earth's surfaces under general conditions including nonradiative heat transfer. We deduce the lowest steady-state temperature attainable and highest net radiative cooling power density available as a function of temperature. We present the exact spectral emissivity that can reach such limiting values, and show that the previously used 8–13 μm atmospheric window is highly inappropriate in low-temperature cases. The critical need for materials with simultaneously optimized optical and thermal properties is also identified. These results provide a reference against which radiative coolers can be benchmarked.

Highlights

We investigate the fundamental limit of radiative cooling of objects on the Earth’s surfaces under general conditions including nonradiative heat transfer
The transparency window in the long-wavelength infrared, which ranges from 8 to 13 μm, has received great attention because it allows for below-ambient cooling without energy consumption[2,3,4,5,6,7,8,9,10,11,12,13,14,15]
The principle of this spontaneous cooling is based on thermal radiation in the transparency window being able to transfer heat between an object on the Earth’s surface and the cold outer space without being blocked by the atmosphere

Summary

Introduction

We investigate the fundamental limit of radiative cooling of objects on the Earth’s surfaces under general conditions including nonradiative heat transfer. We present the ideal spectral emissivity under general conditions that realizes the ultimate lower bound of the temperature of a radiatively cooled object on earth.

Results

Conclusion