Cyclic active refrigerators

TL;DR

This paper introduces cyclic active refrigerators, revealing their potential to surpass traditional efficiency bounds and exhibit Maxwell's demon-like behavior, with models demonstrating these phenomena analytically and numerically.

Contribution

It presents the concept of cyclic active refrigerators, showing they can outperform passive bounds and behave like Maxwell's demons, supported by analytical and numerical models.

Findings

Naive COP can exceed standard bounds

Active systems can act as Maxwell's demons

Hybrid engine-refrigerator phase exists

Abstract

Thermodynamic cycles are idealized processes that can convert heat into work or produce heat flow against a temperature gradient with the input of work. They remain an active area of research in modern stochastic thermodynamics. In particular, cyclic active heat engines have been shown to display a rich phenomenology, such as ``violations'' of the Carnot bound on efficiency and an improved performance in comparison to their passive counterparts. We introduce the concept of cyclic active refrigerators using a previously derived second law for cyclic active systems. We show that for cyclic active refrigerators, a naive definition of the coefficient of performance can exceed the bound set by the standard second law for passive refrigerators. We also show that cyclic active systems can behave like a Maxwell's demon, with heat flowing from the cold to the hot reservoir without any work input. Beyond this phase, cyclic active systems can enter a hybrid phase, functioning as both a heat engine and a refrigerator simultaneously. Our results are obtained with two models that involve active Brownian particles, a simpler one that allows for analytical results and a more realistic one that is analyzed through numerical simulations.