Numerical research of characteristic mixing times of isothermal three-component steam-gas systems

Abstract

Multicomponent diffusion in gases is characterized by a number of effects that are not observed in binary diffusion. Analysis of existing works shows that convective instability may occur in some systems with significantly different diffusion coefficients with certain geometric and thermophysical characteristics. Stability analysis allows determining the spectrum of parameters at which a transition from a diffusive state to a convective is possible. However, this approach does not allow the researchers to investigate the dynamics of the process. Therefore, this work aims to describe emergence and evolution of convective flows in threecomponent systems and assess the influence of the initial composition on the occurrence of concentration gravitational convection. The main part of the work presents a mathematical model describing the occurrence of convective flows based on the splitting scheme according to physical parameters. Numerical data on the concentration fields of the gas with the highest molecular weight at various time points is obtained. It is established that curvature of the isoconcentration lines of the diffusing components can be associated with instability of the mechanical equilibrium of the system. Degree of curvature is determined by the initial concentration of components of the mixture. The obtained data can be used to determine the main characteristics of mass transfer used in calculations related to combined heat and mass transfer in a wide range of thermophysical parameters.