Principle of Maximum Entropy Applied to Rayleigh-B\'enard Convection

TL;DR

This paper applies the maximum entropy principle to Rayleigh-Bénard convection, deriving hydrodynamic equations from microscopic theory and showing entropy increases during the transition to convection, supporting the principle's validity.

Contribution

It provides a microscopic derivation of hydrodynamics and entropy for convection, demonstrating the maximum entropy principle in a nonequilibrium steady state.

Findings

Entropy increases monotonically during convective transition

Maximum entropy principle holds for Rayleigh-Bénard convection

Explains Nusselt number enhancement through entropy considerations

Abstract

A statistical-mechanical investigation is performed on Rayleigh-B\'enard convection of a dilute classical gas starting from the Boltzmann equation. We first present a microscopic derivation of basic hydrodynamic equations and an expression of entropy appropriate for the convection. This includes an alternative justification for the Oberbeck-Boussinesq approximation. We then calculate entropy change through the convective transition choosing mechanical quantities as independent variables. Above the critical Rayleigh number, the system is found to evolve from the heat-conducting uniform state towards the convective roll state with monotonic increase of entropy on the average. Thus, the principle of maximum entropy proposed for nonequilibrium steady states in a preceding paper is indeed obeyed in this prototype example. The principle also provides a natural explanation for the enhancement of the Nusselt number in convection.