The Importance of Coupling between Thermal and Molar Fluxes in a Nitrogen-Oxygen Distillation Column

A model for the transfer of mass and thermal energy in a vapour-liquid region is used to investigate the influence of neglecting coupling on the transfer rates. As an example, we studied a nitrogen-oxygen distillation column. Using a combination of stage and point boundary conditions, a nitrogen transfer profile is obtained that shows the same trend as a profile based on an equilibrium stage distillation model. The distribution of the total transfer over the two column halves is not in agreement, however. This disagreement can be expected to decrease when the dependency of the vapour film thickness on the vapour flow rate and the vapour viscosity is included in the model. The effect of neglecting coupling on the calculated transfer rates changes along the length of the column. The total effect is considerable and should be taken into account in models for the transfer of mass and thermal energy through an interface