Diverging, but negligible power at Carnot efficiency: theory and experiment

Viktor Holubec, Artem Ryabov

Published 2017-08-21Version 1

Recently, a number of studies appeared suggesting possibility of reaching the Carnot efficiency by heat engines (HEs) operating out of quasi-static conditions and thus at a nonzero power. For various distinct classes of models widely used to describe performance of actual HEs, we discuss parameter regimes for which this can happen with a special focus on the magnitude of the output power. These models comprise quantum thermoelectric devices, linear irreversible HEs, minimally nonlinear irreversible HEs, HEs working in the regime of low dissipation, over-damped stochastic HEs and an under-damped stochastic HE. Although the Carnot efficiency can be in some of these models reached at a nonzero and even diverging power, the magnitude of this power is always negligibly small compared to the maximum power attainable in these systems. Our analysis yields conditions under which the Carnot efficiency can be reached out of equilibrium in the individual models and explains new practical aspects inevitably connected with HEs working close to the Carnot efficiency at a large power output. Furthermore, we present a detailed theoretical study of a realistic Brownian HE which can be used for testing our findings in practice adopting available micromanipulation techniques.