Maximum efficiency of steady-state heat engines at arbitrary power

TL;DR

This paper derives a universal upper bound on the efficiency of steady-state heat engines operating at any fixed power, showing that slightly reducing power can significantly increase efficiency.

Contribution

It provides a universal efficiency bound in linear irreversible thermodynamics and quantifies the efficiency gain from reducing power below its maximum.

Findings

Universal efficiency upper bound at fixed power

Efficiency gain from slight power reduction

Exact expression for efficiency improvement

Abstract

We discuss the efficiency of a heat engine operating in a nonequilibrium steady state maintained by two heat reservoirs. Within the general framework of linear irreversible thermodynamics we derive a universal upper bound on the efficiency of the engine operating at arbitrary fixed power. Furthermore, we show that a slight decrease of the power below its maximal value can lead to a significant gain in efficiency. The presented analysis yields the exact expression for this gain and the corresponding upper bound.