A Variational Formulation for Irreversible Thermodynamics with Path Dependence

TL;DR

This paper presents a new mathematical framework for modeling irreversible thermodynamics that naturally incorporates heat and entropy.

Contribution

A novel path-dependent energy Lagrangian is introduced that avoids Lagrange multipliers and Rayleigh potentials.

Findings

The formulation enforces Helmholtz conjugacy and positive heat capacity through an explicit θs term.

A unified action and consistent entropy production are achieved across coupled dissipative mechanisms.

Classical thermodynamic closures emerge as special cases of the proposed functional.

Abstract

This work introduces a path-dependent energy Lagrangian for irreversible thermomechanics that embeds heat and entropy accounting directly into the action. The formulation requires neither Lagrange multipliers nor Rayleigh potentials. An explicit θs term enforces Helmholtz conjugacy and positive heat capacity; writing heat as a divergence produces the natural flux; nonnegative dissipative productions are collected in a single modular term; and a history integral supplies an upper-limit variation that converts instantaneous power into entropy production. Stationarity yields the standard field equations together with a global entropy balance and a channel-wise power identity by placing each production once in entropy and once, with opposite sign, in its own channel. Classical closures—including Fourier and non-Fourier heat conduction, diffusion, and viscous mechanics—arise as special cases of the same functional. Compact examples show how the framework provides a unified action, a single entropy audit, and consistent positive production across coupled dissipative mechanisms.

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