Diffusion instability in three-component gas mixtures containing greenhouse gas

Abstract

The work discusses the influence of pressure and composition of a ternary gas mixture on the possibility of the occurrence of convective instability under isothermal conditions due to differences in the diffusion abilities of the components. The change in “diffusion – concentration gravitational convection” regimes in isothermal ternary gas mixtures CH4 + R12 – Ar, N2 + R12 – n-C4H10 was experimentally studied. It has been shown that instability in the systems under study can occur at a certain content of the component with the highest molecular weight in the mixture. Its further increment in the initial composition of the mixture leads to the emergence of convective flows and an increase in the intensity of mixing. Experiments have confirmed that pressure also determines the transition from a diffusion state to a convective one. A growth in pressure contributes to an increase in the intensity of convective mixing. For a flat vertical channel at certain values of composition and pressure, nonmonotonic concentration distributions causing a significantly nonlinear density distribution with an extremum, which is unusual from the point of view of diffusion, were recorded. The regions of stable and unstable behavior of the system for a wide range of mixture composition and pressure are studied in terms of Rayleigh numbers. The location of the areas where diffusion and instability occur is compared with the results of the experiments.

Keywords

• Diffusion
• Convection
• Diffusion instability
• Concentration distribution
• Greenhouse gas
• Stability map