NONSIMILAR SOLUTIONS FOR LAMINAR FILM CONDENSATION ON A VERTICAL SURFACE

A general computer program has been developed which solves the finite difference analogue of the conservation equations in boundary layer form for laminar film condensation. In addition, closed form analytical solutions based on the Nusselt assumptions have been extended to include the effect of a nonisothermal condenser wall. In so doing, a reference temperature for evaluating locally variable fluid properties is defined in the form Tr = Tw + α(Ts - Tw) and accounts for both the effects of fluid property variations and minor errors introduced by the Nusselt assumptions. In the numerical as well as the analytical developments, vapor drag was accounted for by means of an asymptotic solution of the vapor boundary layer under strong suction which is valid for most engineering situations. This paper evaluates the validity of the extended Nusselt result in terms of the effects of (i) forced vapor flow, (ii) variable wall temperature, and (iii) variable fluid properties. Ten fluids were investigated, including water, all having Prandtl numbers greater than unity. It was found, except for severe wall temperature variations, that a value of α dependent only on fluid specie led to a less than 2 per cent discrepancy between the analytical predictions and the numerical results. © 1969.