Exergy in near-field electromagnetic heat transfer

Abstract

The maximum amount of usable work extractable from a given radiative heat flow defines the exergy. It was recently noted that the exergy in near-field radiative heat transfer can exceed that in the far-field. Here, we derive a closed form formula of exergy in the near-field heat transfer between two parallel surfaces. This formula reveals that, for a given resonant frequency, the maximum exergy depends critically on the resonant linewidth, and there exists an optimal choice of the linewidth that maximizes the exergy. Guided by the analytical result, we show numerically that with a proper choice of doping concentration, the heat flow between two properly designed SiC-coated heavily doped silicon regions can possess exergy that is significantly higher compared to the heat flow between two SiC regions where the heat flow is carried out by phonon-polaritons. Our work indicates significant opportunities for either controlling material properties or enhancing the fundamental potential for near-field heat transfer in thermal energy conversion through the approach of meta-material engineering.