Degree of coupling and efficiency of energy converters far-from-equilibrium

TL;DR

This paper introduces a new matrix framework to analyze the efficiency of energy converters far from equilibrium, establishing universal bounds and trade-offs based on coupling degrees, with applications to heat converters and molecular motors.

Contribution

It generalizes the Onsager matrix to non-equilibrium states, enabling efficiency bounds and power-efficiency trade-offs far from equilibrium.

Findings

Universal efficiency bounds depending on coupling degree.

New power-efficiency trade-offs surpass previous uncertainty relation limits.

Applications demonstrated on heat converters and molecular motor models.

Abstract

In this paper, we introduce a real symmetric and positive semi-definite matrix, which we call the non-equilibrium conductance matrix, and which generalizes the Onsager response matrix for a system in a non-equilibrium stationary state. We then express the thermodynamic efficiency in terms of the coefficients of this matrix using a parametrization similar to the one used near equilibrium. This framework, then valid arbitrarily far from equilibrium allows to set bounds on the thermodynamic efficiency by a universal function depending only on the degree of coupling between input and output currents. It also leads to new general power-efficiency trade-offs valid for macroscopic machines that are compared to trade-offs previously obtained from uncertainty relations. We illustrate our results on an unicycle heat to heat converter and on a discrete model of molecular motor.