An elliptic two-phase numerical model of laminar film condensation from a steam-air mixture flowing over a horizontal tube

A complete two-phase numerical model of film condensation from a steam-air mixture flowing downward over an isothermal horizontal tube is presented. The model uses the full 2D elliptic Navier-Stokes equations and predicts the full viscous flow and heat and mass transfer in the mixture and in the entire condensate film from the top of the tube to the falling film below the tube. The numerical model implements a dynamically moving non-orthogonal computational grid that tracks the phase interface sharply. An adaptive-grid Eulerian method is followed in which the phase interface is moved at the end of each time step. The model uses a segregated solution method based on a finite volume approach in which fundamental balances of mass, energy, and force are enforced accurately at the phase interface. The results from the new model are compared with available theoretical studies. Finally, new results are presented on the effects of free stream gas mass fraction, free-stream-to-tube temperature difference, upstream Reynolds number, and free-stream pressure on the condensate film development, the local and average heat transfer coefficients, and the total liquid mass flow rate.