Probing local equilibrium in nonequilibrium fluids

TL;DR

This study uses computer simulations to demonstrate that local thermodynamic equilibrium in a 2D hard-disks fluid is a robust property even far from equilibrium, revealing bulk-boundary decoupling and nonlocal effects.

Contribution

It provides the first detailed numerical evidence that LTE holds strongly in nonequilibrium fluids, enabling precise equation of state measurements far from equilibrium.

Findings

Macroscopic LTE is stronger than previously thought.

Bulk-boundary decoupling occurs in nonequilibrium fluids.

Energy fluctuation corrections indicate nonlocality of the nonequilibrium potential.

Abstract

We use extensive computer simulations to probe local thermodynamic equilibrium (LTE) in a quintessential model fluid, the two-dimensional hard-disks system. We show that macroscopic LTE is a property much stronger than previously anticipated, even in the presence of important finite size effects, revealing a remarkable bulk-boundary decoupling phenomenon in fluids out of equilibrium. This allows us to measure the fluid's equation of state in simulations far from equilibrium, with an excellent accuracy comparable to the best equilibrium simulations. Subtle corrections to LTE are found in the fluctuations of the total energy which strongly point out to the nonlocality of the nonequilibrium potential governing the fluid's macroscopic behavior out of equilibrium.