Effect of molecular weight ratio on diffusion of light gases into air

Abstract

We propose a numerical study on the effect of density of light gases on the behavior of a gas mixture (gas–air) in confined spaces and subjected to gradients of temperature and concentration. The diffusion of light gases requires the use of an appropriate model called low Mach number instead of the Boussinesq approximation which is not valid in such a situation. To solve the coupled momentum, energy, and concentration equations, an iterative methodology based on finite volume method using the low Mach number approximation was required. Representative results illustrating the effects of molecular weight ratio on the thermophysical and thermodynamic properties are reported. The average thermal and mass transfer rates on the active wall are presented and discussed. The results show that the hydrogen–air diffusion exhibits a particular behavior toward the compressibility of the binary mixtures. It is also found that the Boussinesq model is not sufficient to simulate diffusion of very light gases into air.