Entropidissipation

Entropidissipation is a term used in non‑equilibrium thermodynamics to denote the rate at which entropy is dissipated within a system due to irreversible processes. It is closely related to the concept of entropy production (or generation) and is constrained by the second law of thermodynamics, which requires non‑negativity for closed systems.

In continuum descriptions, the local rate of entropidissipation per unit volume is often expressed as a sum of products of thermodynamic fluxes and their conjugate forces: sigma = sum_i J_i X_i. Examples include heat conduction (where the heat flux J_q and the temperature gradient act as the force), viscous dissipation (conversion of mechanical energy into heat), mass diffusion, and chemical reactions. The total entropidissipation is the integral of sigma over the system volume; in steady states it can balance the entropy fluxes across boundaries.

Entropidissipation is distinct from, yet related to, entropy flow, which describes entropy carried into or out of a system by matter and radiation. The internal production of entropy (entropidissipation) and external entropy exchange together determine the net change in a system’s entropy.

In statistical mechanics and stochastic thermodynamics, entropy production along microscopic trajectories provides a microscopic account of entropidissipation and connects to fluctuation theorems. The term is sometimes used interchangeably with entropy production, though some authors reserve entropidissipation to emphasize irreversible degradation of a system’s availability rather than net entropy change alone.

See also: entropy production, entropy flow, irreversible thermodynamics.