Ideal spectral emissivity for radiative cooling of earthbound objects

Area of Science:

• Thermodynamics
• Materials Science
• Optics

Background:

• Radiative cooling offers a passive method for heat dissipation.
• Current understanding of radiative cooling limits often overlooks nonradiative heat transfer.
• Optimizing materials for radiative cooling is essential for efficient thermal management.

Purpose of the Study:

• To determine the fundamental limits of radiative cooling under general conditions.
• To identify the lowest attainable steady-state temperatures and highest net radiative cooling power densities.
• To guide the development of advanced radiative cooling materials.

Main Methods:

• Theoretical deduction of steady-state temperature limits.
• Analysis of net radiative cooling power density as a function of temperature.
• Spectral emissivity calculations for optimal cooling.

Main Results:

• Established fundamental limits for radiative cooling, incorporating nonradiative heat transfer.
• Demonstrated that the 8-13 μm atmospheric window is suboptimal for low-temperature radiative cooling.
• Identified the necessity for materials with simultaneously optimized optical and thermal properties.

Conclusions:

• The study provides a theoretical benchmark for radiative cooler performance.
• Rethinking spectral emissivity optimization is crucial, especially for low-temperature applications.
• Future advancements in radiative cooling depend on materials engineered for specific optical and thermal characteristics.