Adiabatic heating and convection in a porous medium filled with a near-critical fluid.

Dynamics and heat transfer in a porous medium filled with a fluid phase at parameters near the gas-liquid critical point are studied. A two-dimensional numerical solver based on the hydrodynamic model for a porous medium with a high compressible fluid phase including the van der Waals equation of state is used. In weightlessness, adiabatic heating of fluid phase under the step-temperature heat supply is investigated analytically and numerically. In terrestrial conditions, gravity-driven convection in vertical rectangular cells generated by lateral heating in unsteady and steady-state regimes is simulated. The effects of high compressibility of near-critical fluid phase on convection are studied. Convective motions and heat transfer in horizontal rectangular cells consisting of two porous layers at different porosity and permeability heated from below are simulated as well. Adiabatic heating subjected to hydrostatic compressibility effects, the onset and development of convection, and convective structures in a steady-state regime are analyzed.

Hydrostatic compressibility phenomena: new opportunities for near-critical research in microgravity.

Peculiarities of the isothermal and isentropic equilibrium in highly compressible media with nonperfect state equations are discussed. Formulation of the adiabatic temperature gradient using Schwarzschild criterion and equilibrium equations for nonperfect gas are considered. Criterion for the onset of convection in the van der Waals (VDW) gas is examined using direct numerical modeling on the basis of equation for convection in compressible viscous nonperfect gas. Results of three-dimensional modeling near-critical convection in the vicinity of the convection onset in space flight with quasi-steady microaccelerations are given. A proposal for the microgravity research of the near-critical convection is discussed.

Unsteady near-critical flows in microgravity.

This paper presents analysis of the different time scales associated with unsteady fluid flow phenomena near the thermodynamical critical point and that are typical for experiments carried out in microgravity. A focus of the paper is modeling the initial stage of convection under low and zero gravity on the basis of the two-dimensional Navier-Stokes equations for a compressible gas with the Van der Waals state equation. We also consider a thermoacoustic problem on the basis of three-dimensional linearized equations for an isentropic inviscid gas near the critical point in zero gravity. We compare the heat transfer due to unsteady convection and the piston effect in an enclosure with side heating in zero and low gravity with pure conductivity.

Adiabatic heating and convection caused by a fixed-heat-flux source in a near-critical fluid.

Dynamics and heat transfer in a near-critical fluid in a square cavity with a finite heat source located at the bottom are studied numerically. A thermally insulated enclosure and a fixed-heat-flux source are considered. The two-dimensional simulation is based on the full Navier-Stokes equations with two-scale splitting of the pressure and the van der Waals equation of state. It is shown that the piston effect is independent of convection. Near the critical point, this effect becomes independent of criticality and convective motions are damped.