Film condensation of saturated and superheated vapors along isothermal vertical surfaces in mixed convection

An analysis for condensation from an isothermal vertical flat plate in mired convection is reported. The entire mixed convection regime is divided into two regions. One region covers the forced-convection-dominated regime, and the other covers the-free-convection-dominated regime. The governing system of equations is first transformed into a dimensionless form by the nonsimilar transformation, separately for each regime, and then solved using the local nonsimilarity method along with a finite difference scheme. Two nonsimilarity parameters are introduced. The parameter xi(f) = Gr(x) / Re-x(2) characterizes the effect of buoyancy force on forced convection, while the parameter xi(f) = Re-x / Gr(x)(1/2) characterizes the effect of forced flow on free convection. Numerical results for pure steam and refrigerant R-134a are presented for both saturated and superheated cases. If is found that the buoyancy force significantly increases the wall shear stress and condensate mass flux To a lesser degree, the buoyancy force also increases the wad heat flux. Superheating is found to have an insignificant effect on wall heat flux for a pure vapor.