Effect of nature and composition of inert gas on binary vapour condensation

Abstract

We consider the problem of binary vapour condensation in the presence of an inert gas and analyse the effect of the nature of the inert gas and its composition on the condensation process. The analysis of the simultaneous heat and mass transfer process is carried out with the aid of two basically different models for vapour phase transfer: (i) an interacting̲ model in which the diffusional interactions in the vapour phase are properly taken into account and (ii) a non - interacting̲ model in which the diffusion process in the vapour phase is modelled using effective pseudo-binary diffusivities. These two models are applied to specific cases involving the condensation of methanol-water vapour mixtures in the presence of air and also in the presence of helium. Two cases involving rich and lean vapour mixtures are considered. The results of the computations show that interaction effects in the vapour phase are significant for rich vapour mixtures (small concentrations of inert gas). Also, the interactions in the system methanol-water vapour-helium are much larger than in the corresponding system with air as inert gas. The enhanced effect of diffusional interactions in the helium system is attributable to larger differences in the constituent binary pair diffusivities.