ZAPPOLI, Bernard; CHERRIER, Raphaël; LASSEUX, Didier; OUAZZANI, Jalil; GARRABOS, Yves

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ZAPPOLI, Bernard
Physique et mécanique des milieux hétérogènes [PMMH]

CHERRIER, Raphaël
Transferts, écoulements, fluides, énergétique [TREFLE]

LASSEUX, Didier
Transferts, écoulements, fluides, énergétique [TREFLE]

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Document de travail - Pré-publication

Résumé en anglais

We investigate the critical speeding up of heat equilibration by the piston effect (PE) in a nearly supercritical van der Waals (vdW) fluid confined in a homogeneous porous medium. We perform an asymptotic analysis of the averaged linearized mass, momentum and energy equations to describe the response of the medium to a boundary heat flux. While nearing the critical point (CP), we find two universal crossovers depending on porosity, intrinsic permeability and viscosity. Closer to the CP than the first crossover, a pressure gradient appears in the bulk due to viscous effects, the PE characteristic time scale stops decreasing and tends to a constant. In infinitly long samples the temperature penetration depth is larger than the diffusion one indicating that the PE in porous media is not a finite size effect as it is in pure fluids. Closer to the CP, a second cross over appears which is characterized by a pressure gradient in the thermal boundary layer (BL). Beyond this second crossover, the PE time remains constant, the expansion of the fluid in the BL drops down and the PE ultimately fades away.< Réduire

Mots clés en anglais

Critical point

Piston effect

Porous media

Origine

Importé de hal

Unités de recherche

Institut de Chimie de la Matière Condensée de Bordeaux (ICMCB) - UMR 5026