A Bound from Below on the Temperature for the Navier--Stokes--Fourier System

Abstract

We give a uniform bound from below on the temperature for a variant of the compressible Navier-Stokes--Fourier system, under suitable hypotheses. This system of equations forms a mathematical model of the motion of a compressible fluid subject to heat conduction. Building upon the work of [A. Mellet and A. Vasseur, Monatsh. Math., 157 (2009), pp. 143--161], we identify a class of weak solutions satisfying a localized form of the entropy inequality (adapted to measure the set where the temperature becomes small) and use a form of the De Giorgi argument for L∞ bounds of solutions to elliptic equations with bounded measurable coefficients.