Determination of the Boundary of the “Diffusion–Gravitational Convection” Regimes Change in Three-Component Gas Mixtures Containing Real Gases, Taking into Account the Compressibility Factor of the Components Under Isothermal Conditions

The stability analysis for isothermal three-component gas mixtures, in which one of the components exhibits real properties in the considered pressure range, is performed. The system of Navier–Stokes and diffusion equations in the Boussinesq approximation is considered, taking into account analogs of buoyancy effects in a density-stratified medium. The presented solution is obtained by the small-perturbation method using the principle of diffusion independence, while maintaining the condition of neutrality of convective perturbations. Expressions for the boundary between the “diffusion–gravitational convection” regimes are obtained in terms of partial Rayleigh numbers that account for the compressibility factor of the mixing components. The stability cartograms show that on the stability maps, the position of the boundary of the regimes change depends on the variation in the compressibility factor with a pressure change. When the compressibility factor changes, the values of the critical Rayleigh numbers, which are the intersection points of the boundary of the regimes change and the coordinate axes, decrease. It is established that the behavior of the partial Rayleigh numbers on the plane (Ra1, Ra2) is nonlinear for isothermal ternary mixtures, which have the general form H2 + N2O–N2 and He + CO2–N2, He + R12–Ar, at T = 298.0 K and elevated pressures. It is revealed that when taking into account the compressibility factor of the components, the partial Rayleigh numbers of the components decrease.