Thermodynamic Length, Time, Speed and Optimum Path to Minimize Entropy Production

TL;DR

This paper explores the relationship between thermodynamic length, time, and entropy production, deriving optimal control paths as Riemannian geodesics and proposing practical algorithms for thermodynamic processes.

Contribution

It introduces a novel connection between thermodynamic time scales and kinetic coefficients, deriving Euler-Lagrange equations for optimal thermodynamic control with practical implementation.

Findings

Optimal paths are Riemannian geodesics in thermodynamic space.

Thermodynamic time corresponds to the number of steps in control.

A stepwise algorithm for constant thermodynamic speed control is proposed.

Abstract

In addition to the Riemannian metricization of the thermodynamic state space, local relaxation times offer a natural time scale, too. Generalizing existing proposals, we relate {\it thermodynamic} time scale to the standard kinetic coefficients of irreversible thermodynamics. Criteria for minimum entropy production in slow, slightly irreversible processes are discussed. Euler-Lagrange equations are derived for optimum thermodynamic control for fixed clock-time period as well as for fixed {\it thermodynamic} time period. Only this latter requires constant thermodynamic speed as the optimum control proposed earlier. An easy-to-implement stepwise algorithm is constructed to realize control at constant thermodynamic speed. Since thermodynamic time is shown to correspond to the number of steps, thus the sophisticated task of determining thermodynamic time in real control problems can be substituted by measuring ordinary intensive variables. Most remarkably, optimum paths are Riemannian geodesics which would not be the case had we used ordinary time.