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 mire d convection is reported. The entire mixed convection regime is divided int o two regions. One region covers the forced-convection-dominated regime, an d the other covers the-free-convection-dominated regime. The governing syst em of equations is first transformed into a dimensionless form by the nonsi milar transformation, separately for each regime, and then solved using the local nonsimilarity method along with a finite difference scheme. Two nons imilarity 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-134 a are presented for both saturated and superheated cases. If is found that the buoyancy force significantly increases the wall shear stress and conden sate mass flux To a lesser degree, the buoyancy force also increases the wa d heat flux. Superheating is found to have an insignificant effect on wall heat flux for a pure vapor.