Onset and Nonlinear Regimes of Convection of Ternary Mixture in a Rectangular Porous Cavity Taking into Account the Soret Effect

Abstract

The onset and nonlinear regimes of the Soret-induced convection in a mixture of dodecane, isobutylbenzene, and tetralin, taken in equal mass fractions and placed in a rectangular porous cavity with rigid impermeable boundaries elongated in the horizontal direction and heated from below, have been numerically investigated. The vertical boundaries of the cavity are thermally insulated. The components of the mixture under consideration are representatives of the main groups of chemical compounds that are oil components. The values of the porosity and permeability of the medium were chosen to be close to the values of real media, such as sand, sandstone, or limestone. The area of such a configuration simulates a hydrocarbon field. Due to the Soret effect (thermal diffusion), the light components of the mixture with positive separation ratios (dodecane and isobutylbenzene) are accumulated in the hot region, whereas the heavy component (tetralin) is accumulated in the cold region. In the case of heating from below (provided by the presence of geothermal gradient under natural conditions), this process may induce convection. It was found that a steady flow occurs in the cavity at a certain value of Rayleigh number; this flow becomes oscillatory with an increase in the Rayleigh number. With a further increase in the Rayleigh number, irregular oscillations arise. Several monotonic and oscillatory regimes, characterized by different spatial scales (from one to ten vortices), were found in the range of Rayleigh numbers under consideration. The oscillations of instantaneous flow characteristics in oscillatory regimes have a complex shape. A steady-state flow regime with an asymmetric structure was found. The ranges of Rayleigh numbers in which the found regimes may exist and the time dependences of the integral characteristics during the formation of steady flows were determined. The effect of supercriticality on the flow structure and concentration distributions of mixture components were analyzed.