Peculiarities of diffusive and convective mixing in gas mixtures with fine dust in isobaric-isothermal conditions

Abstract

This paper presents a numerical study of diffusive–convective mixing in gas–solid systems under isothermal and isobaric conditions. Two model systems, CO₂ + Si – N₂ and H₂O + C – Air, were investigated to analyze the transport of gas components and dispersed solid particles. Simulations were performed in the ANSYS Fluent environment using the Species Transport and Eulerian Multiphase Flow models, enabling the coupled description of gas-phase diffusion and particle motion. Calculations were carried out for a two dimensional vertical channel geometry previously employed in studies of gas–gas mixing, where instability of mechanical equilibrium in the diffusion layer was observed. The results show that the dispersed solid phase forms localized regions of increased density that subsequently undergo gravitational displacement, leading to the development of convective structures and intensive mixing. At later stages, the system evolves toward a quasi-stationary concentration distribution. The study extends a previously validated numerical approach for gas mixtures to gas–solid media with different physicochemical properties and demonstrates the formation of Rayleigh Taylor-type structures in the absence of thermal and chemical effects. The proposed methodology provides an effective tool for modeling diffusion–convective processes in multiphase systems and may be applied to the analysis of aerosol transport and dust particle dynamics in both atmospheric and technological environments.

Key words: diffusion, convection, instability, Eulerian model, numerical modeling, ANSYS Fluent, Rayleigh-Taylor instability.