Tight coupling in thermal Brownian motors

TL;DR

This paper analytically investigates a thermal Brownian motor, demonstrating tight coupling conditions, the attainment of Carnot efficiency at slow velocities, and the maximum efficiency at maximum power, with implications for Brownian refrigeration.

Contribution

It provides an exact analytical calculation of Onsager coefficients and elucidates the conditions for tight coupling and maximum efficiency in thermal Brownian motors.

Findings

Onsager reciprocity holds in the model.

Determinant of Onsager matrix vanishes, indicating tight coupling.

Efficiency at maximum power reaches the Curzon-Alhborn bound.

Abstract

We study analytically a thermal Brownian motor model and calculate exactly the Onsager coefficients. We show how the reciprocity relation holds and that the determinant of the Onsager matrix vanishes. Such condition implies that the device is built with tight coupling. This explains why Carnot's efficiency can be achieved in the limit of infinitely slow velocities. We also prove that the efficiency at maximum power has the maximum possible value, which corresponds to the Curzon-Alhborn bound. Finally, we discuss the model acting as a Brownian refrigerator.