Numerical solution of film condensation from turbulent flow of vapor–gas mixtures in vertical tubes

A complete two-phase model is presented for film condensation from turbulent downward flow of vapor–gas mixtures in a vertical tube. The model solves the complete parabolic governing equations in both phases including a model for turbulence in each phase, with no need for additional correlation equations for interfacial heat and mass transfer. A finite volume method is used to form the discretized mean flow equations for conservation of mass, momentum, and energy. A fully coupled solution approach is used with a mesh that automatically adapts to the changing film thickness. The results of using three turbulence models involving combinations of mixing length and k–e models in the film and mixture regions are compared. This new model is extensively compared with previous numerical and experimental studies. In the experimental comparisons, it was found that a model consisting of a k–e turbulence model for both the film and the mixture flows produced the best agreement. Results are also presented for a parametric study of condensation from steam-air mixtures. The effects of changes to the inlet Reynolds number, the inlet gas mass fraction, and the inlet-to-wall temperature difference on the film thickness and heat transfer are presented and discussed. Local profiles of axial velocity, temperature, and gas mass fraction are also presented.