Coupled Transfer in a Diffusion Problem: Concentration Gradient in the Coexisting Liquid-Like and Gas-Like States

Abstract

AbstractThis chapter also belongs to the first part of this thesis, where a diffusion problem is studied and coupled heat and mass transfer exists through cross-diffusion effects. The steady-state responses of an enclosed binary mixture subjected to transcritical temperature differences under supercritical pressures are numerically simulated to study the coexistence of liquid-like and gas-like states and the influences of the concentration gradient. It is found that the steady state is strongly nonlinear in state variables and physical properties. The Soret effect induces the concentration gradient, and the low heat conducting nature of gas-like state compared to the liquid-like one gives rise to the pressure drop. As the critical pressure is approached and the temperature difference is enlarged, the profiles of state variables own growing nonlinearities. Under near-critical conditions, the concentration gradient has deep effects on the relative variations of density and pressure. Therefore, it plays a vital role in buoyancy flows and transient phenomena like the piston effect.