Cross diffusion effects in the interfacial mass and heat transfer of multicomponent droplets

Abstract

Realistic mathematical modeling of multicomponent mixtures is highly complex due to diffusive phenomena (cross diffusion effects) not described by Fick’s law. The Maxwell–Stefan equations and generalized Fick’s law can represent all possible interactions in multicomponent mixtures and, thus, the effects of cross diffusion are considered. The present work was planned to study the interfacial heat and mass transfer and cross diffusion effects in a multicomponent mixture. For this purpose, three computational routines based on a constant diffusion coefficient model, on the effective diffusivity model and on the Maxwell–Stefan equations along with the generalized Fick’s law were developed. The models were applied to study mass and heat transfer in a binary air–water mixture and in a multicomponent mixture composed of methane, n-pentane, n-hexane and n-octane. The equilibrium achieved in the CFD studies was verified with data obtained from a psychrometric chart, (for the binary mixture), and the values obtained by the process simulator PRO/II® (for the multicomponent mixture). It was found that the cross diffusion effects were not significant in the mixture studied, leading to the conclusion that simpler approaches, such as the effective diffusivity model, can be used to describe the mass transfer in ideal multicomponent mixtures.