Mixing of carbon dioxide dissolved in a multicomponent gas mixture at different pressures was researched. It was found that the mechanical equilibrium of the ternary gas mixture 0.4163H2 (1) + 0.5837CO2 (2) − N2 (3) is violated at a pressure of p = 0.7 MPa and structured flows appear in the system. The pressure area (from 0.7 to 1.5 MPa) at which the conditions of priority transfer of components with the highest molecular weight in the mixture are realised in the system is fixed. To analyse the effect of pressure on the process of changing “diffusion–convection” modes, a mathematical model, which takes into account the kinetic features of multicomponent mixing, was applied. It was shown that the change in the modes of mass transfer is associated with a significant difference in the diffusion ability of the components. It is noted that the difference in the diffusion coefficients of components results in the nonlinearity of the concentration distribution, which leads to the inversion of the density gradient of the gas mixture, which is the cause of convective flows.

The mixing of carbon dioxide dissolved in multicomponent gas mixtures at various pressures was studied. It was found that at a certain pressure the diffusion separation of components is violated and structured flows arise in the system. The pressure regions are fixed at which the conditions of priority transfer of the component with the highest molecular weight in the mixture are realized in the system. To analyze the effect of pressure on the process of changing the diffusion – convection modes, a mathematical model has been proposed that takes into account the kinetic features of multicomponent mixing. It is shown that the change in mass transfer modes is associated with a significant difference in the diffusion abilities of the components.

In isothermal three-component gas mixtures in quasi-stationary conditions the procedure of numerical solution of Stefan-Maxwell diffusion equations using the software package “MathCad” is considered. It is shown that one of the specific features of multicomponent diffusion is the appearance of nonlinear concentration distributions of components in vertical channels. Due to the difference in the coefficients of mutual diffusion of gases in some systems under certain conditions, nonlinear distributions of component concentrations lead to a non-monotonic distribution of the density of the gas mixture. By the example of hydrogen – nitrogen – methane and methane – n-butane – nitrogen systems at a constant temperature T = 298 K, the influence of the content of the component with the highest molecular weight in the triple gas mixture on the degree of nonlinearity of the density distribution in the diffusion channel is analyzed. It is suggested that the inversion of the density distribution of the mixture may be the cause of convective instability in triple gas systems. The results of calculations are compared with experimental data.

Using methods of numerical simulation, we studied the quasi-stationary mass transfer of isothermal ternary gas mixtures in the vertical and inclined channels for the zone of flow exit from a given channel into the lower flask of a diffusion cell. Convective mixing is considered under conditions involving an increase in the density of the mixture with the height of the channel. The characteristic features of structured flows were studied at a certain content of the component with the highest molecular weight in the mixture. The convective formations in the vertical and inclined channels are compared. The dynamics of structured convective flows at various inclination angles is analysed. Estimates of the lifetime of a structural formation consisting mainly of the component with the highest molecular weight moving in a gas mixture with a lower density value are given.

On the basis of the software package "MathCad", by solving the Stefan-Maxwell diffusion equations, the evolution of the features of mass transfer in a three-component gas mixture, depending on pressure changes, has been numerically studied. In this analysis, the mixing process is studied in a vertical cylindrical channel of a finite size and at the isothermal conditions. The governing equations are solved at the boundary conditions assuming the absence of matter transfer through the walls of diffusion channel. Through the Rayleigh partial numbers, the influence of the pressure change on the behaviour of diffusion and convective flows is examined. The numerical results reveal that an increase in the pressure leads to a change of modes in ternary gas mixture. The present results are in good agreement with the existing experimental data.