Effect of viscous friction on entropy, entropy production and entropy extraction rates in underdamped and overdamped media

TL;DR

This paper derives general thermodynamic expressions for entropy production, free energy, and entropy extraction rates in Brownian particles within media with spatially and temporally varying viscous friction, analyzing their non-equilibrium behavior.

Contribution

It introduces new analytical formulas for entropy-related rates in underdamped and overdamped media with variable viscosity, extending stochastic thermodynamics to these complex systems.

Findings

Entropy production approaches zero without load in uniform temperature systems.

Entropy increases and saturates over time when viscous friction decreases with load.

Systems with increasing viscous friction show higher entropy production and irreversibility.

Abstract

Considering viscous friction that varies spatially and temporally, the general expressions for entropy production, free energy, and entropy extraction rates are derived to a Brownian particle that walks in an overdamped and underdamped media. Via the well known stochastic approaches to underdamped and overdamped media, the thermodynamic expressions first derived at trajectory level then generalized to an ensemble level. To study the non-equilibrium thermodynamic features of a Brownian particle that hops in a medium where its viscosity varies on time, a Brownian particle that walks on a periodic isothermal medium (in the presence or absence of load) is considered. The exact analytical results depict that in the absence of load $f=0$, the entropy production rate ${\dot e}_{p}$ approaches the entropy extraction rate ${\dot h}_{d}=0$. This is reasonable since any system which is in contact with a uniform temperature should obey the detail balance condition in a long time limit. In the presence of load and when the viscous friction decreases either spatially or temporally, the entropy $S(t)$ monotonously increases with time and saturates to a constant value as $t$ further steps up. The entropy production rate ${\dot e}_{p}$ decreases in time and at steady state (in the presence of load), ${\dot e}_{p}={\dot h}_{d}>0$. On the contrary, when the viscous friction increases either spatially or temporally, the rate of entropy production as well as the rate of entropy extraction monotonously steps up showing that such systems are inherently irreversible.