Heat transfer in a near-critical fluid saturated porous medium: Piston effect and viscous slowing down

Coupled heat and momentum transfer in a porous medium saturated by a near (super) critical fluid is shown to take place under three different regimes depending on the distance to the critical point (CP). Far enough from the CP, transfer is governed by the classical piston effect (PE). While nearing the CP, the PE is hindered by a pressure gradient that builds up in the bulk of the medium. Exceedingly close to the CP, viscous effects are present in the whole domain, including the boundary layer close to the heated boundary, so that the PE is faded away and heat transfer takes place in a diffusive regime.