Analysis of laminar mixed-convection condensation on isothermal plates using the full boundary-layer equations: mixtures of a vapor and a lighter gas

Laminar film condensation from mixtures of a vapor and a lighter noncondens able gas flowing downward along inclined isothermal plates is investigated numerically using the full boundary-layer equations for the liquid film and the mixture. The adverse net body force due to high concentration of the l ighter gas near the liquid-mixture interface gives rise to the possibility of boundary-layer separation. A numerical solution was developed based on a finite-control-volume method and it was marched along the plate up to the separation location. Results were obtained for three vapor-gas mixtures cov ering a wide range of liquid Prandtl numbers, high gas concentration and hi gh liquid subcooling. Comparisons with previous models (which included vari ous simplifying assumptions) showed that agreement is possible only for con ditions of low gas concentration and liquid subcooling. Results of the sepa ration distance exhibited interesting trends, which are discussed and expla ined. It is also demonstrated that lighter gases can have a more inhibiting effect on heat transfer than heavier gases. (C) 1998 Elsevier Science Ltd. All rights reserved.