Free-Convection Condensation of Air-Steam Mixture on A Vertical Surface : Comparison between Theory and Experiment

Abstract

The two-phase boundary layer equations for free-convection condensation of an air-steam mixure on a vertical flat surface are numerically solved in the bulk air concentration range from 0.18 to 0.98 at 100 kPa. From the results, two correlation equations for convection heat transfer from the bulk to the vapor-liquid interface are obtained; the one contains the effect of the enthalpy diffusion term in the energy equation, and the other is derived from the saturation temperature gradient corresponding to the mass concentration gradient at the vapor-liquid interface. By using these equations, two algebraic equation systems for evaluating the heat flux at the cooling surface and the condensation mass flux are derived. A comparison between the solutions of the algebraic equations and Fujii and Kato's experimental results yields the following conclusions: (1) the theory agrees with the experiment within an error of 10% for the condensation mass flux, and (2) in the case of large bulk air concentration, the heat flux at the cooling surface which is calculated by using the saturation temperature gradient for convection heat flux in the vapor phase agrees well with the experimental results.