Critical dynamics of an isothermal compressible non-ideal fluid

TL;DR

This paper investigates the critical dynamics of an isothermal, compressible non-ideal fluid, revealing a reduction to overdamped sound wave behavior below four dimensions and highlighting divergent bulk viscosity effects.

Contribution

It introduces a scaling and simulation study showing how isothermal critical dynamics reduce to model A with overdamped sound waves below four dimensions.

Findings

Order-parameter dynamics reduce to model A below 4D

Bulk viscosity diverges at criticality

Shear viscosity remains finite above 2D

Abstract

A pure fluid at its critical point shows a dramatic slow-down in its dynamics, due to a divergence of the order-parameter susceptibility and the coefficient of heat transport. Under isothermal conditions, however, sound waves provide the only possible relaxation mechanism for order-parameter fluctuations. Here we study the critical dynamics of an isothermal, compressible non-ideal fluid via scaling arguments and computer simulations of the corresponding fluctuating hydrodynamics equations. We show that, below a critical dimension of 4, the order-parameter dynamics of an isothermal fluid effectively reduces to "model A," characterized by overdamped sound waves and a divergent bulk viscosity. In contrast, the shear viscosity remains finite above two dimensions. Possible applications of the model are discussed.