CONVECTIVE INSTABILITY TRIGGERED BY A DILUTE SOLID PHASE IN THECO2−Si−N2GAS–AEROSOL SYSTEM AT LOW PARTICLE LOADING: ANUMERICAL STUDY

Venera Mukamedenkyzy, Aiya Tolepbergen

2026

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DOI 10.51889/ijapa.2026.1.1.003
Data confidence 70 medium
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Abstract

This paper reports a numerical investigation of diffusion-convective mass transfer in theCO2− Si− N2gas–aerosol system at a low dispersed-phase volume fraction of φ = 0.5% underisothermal and isobaric conditions(T = 300 K, p = 0.1 MPa). Computations were carried out inANSYS Fluent, combining the Species Transport formulation with the Eulerian Multiphase Flowframework, which together capture the coupled motion of gas components and solid microparti-cles with a diameter of 10 μ m. The results demonstrate that even at such a low particle loading,gravitational settling of Si particles generates a local density inversion near the bottom wall ofthe upper vessel – sufficient to trigger convective instability. The mixing evolves through a se-quence of well-defined stages: initial particle sedimentation, formation and subsequent breakupof a dense particle cluster, sustained downward transport through the connecting channel, and theemergence of a characteristic teardrop-shaped solid-phase structure in the lower vessel. Throughoutthis process, the two phases exhibit markedly different transport kinetics: CO2accumulates gradu-ally and continuously, whereas Si migrates in discrete pulses, producing pronounced oscillations inthe dispersed-phase volume fraction. The principal novelty of this work lies in demonstrating thatRayleigh–Taylor-type convective instability develops at φ = 0.5% – a loading level at which anysolid-phase influence on the mass transfer mechanism would not be expected a priori. This find-ing points to the existence of a lower concentration threshold below which the system transitionsfrom gas–like diffusive behavior to a qualitatively different convection-driven regime. The com-bined Species Transport and Eulerian Multiphase approach proves capable of reproducing diffusion– convective dynamics in dilute gas–solid systems without recourse to empirical fitting parameters.The outcomes of this study are relevant to modeling aerosol particle behavior under atmosphericand industrial conditions, and may inform the design of experiments aimed at measuring mutualdiffusion coefficients in gas–aerosol systems.