Condensation of vapour mixtures .1.

Two substantial differences exist between the condensation of flowing vapour mixtures and pure vapours. Firstly, in the case of a mixture, the compositional and thus the physical properties of both vapour and liquid phase change along the condensation path. Secondly, the mass transfer in the vapour between phase determines in the most cases the whole condensation kinetic. On the contrary, the condensation of pure vapours is controled only by heat transfer in the liquid phase. The present paper deals with the simultaneous heat and mass transfer processes during multicomponent condensation using the film model. The interaction between the components and the mass transfer in the vapour phase are analysed on the basis of the Maxwell-Stefan-equations. In addition to the exact matrix solution of these equations, some of their approximate solutions are also included into the considerations and compared with experiments. The results obtained with the film model are mostly in good agreement with experimental data, especially for simple flow geometry, e.g. condensation in a vertical tube. The exact solution of the Maxwell-Stefan-equations leads to a better agreement between the calculations and the experiments than the simple approximate methods. The agreement is generally less satisfactory for complex flow configurations as for example of a condensation in a horizontal shell-and-tube condenser with baffels. Here improvements seem to be necessary not only with regard to the interactions between the mixture components, but also with regard to the calculations of binary mass transfer coefficients which are necessary for the use of the film model.