Efficiency of a two-stage heat engine at optimal power

TL;DR

This paper introduces a two-stage finite-time heat engine model operating between reservoirs, analyzing its efficiency at maximum power and revealing universal efficiency behaviors up to second order in Carnot efficiency.

Contribution

It develops a novel two-stage cycle model with tight coupling and low dissipation, deriving efficiency bounds and universality properties at maximum power.

Findings

Curzon-Ahlborn efficiency as a lower bound

Universal efficiency behavior up to second order in Carnot efficiency

Explicit dissipation constants related to heat transfer and capacity

Abstract

We propose a two-stage cycle for an optimized linear-irreversible heat engine that operates, in a finite time, between a hot (cold) reservoir and a finite auxiliary system acting as a sink (source) in the first (second) stage. Under the tight-coupling condition, the engine shows the low-dissipation behavior in each stage, i.e. the entropy generated depends inversely on the duration of the process. The phenomenological dissipation constants are determined within the theory itself in terms of the heat transfer coefficients and the heat capacity of the auxiliary system. We study the efficiency at maximum power and highlight a class of efficiencies in the symmetric case that show universality up to second order in Carnot efficiency, while Curzon-Ahlborn efficiency is obtained as the lower bound for this class.