On the heat transfer in dropwise condensation

Abstract

A population balance model is used, for the case when no experimental data or theoretical formulae are available, to derive the drop size distribution of small drops which grow mainly by direct condensation. This is combined with the well-known size distribution for large drops which grow mainly by coalescence and with the growth rate of single drops to compute the heat flux during the process of dropwise condensation. The computation can be simplified by neglecting all the relatively unimportant resistances except the resistance to heat conduction through the drop body. The vapor-side heat transfer coefficient of dropwise condensation can be estimated sufficiently accurately by the simple equation ▪ where r e is half the mean spacing between the active nucleation sites on the substrate surface and r max is the maximum drop radius. A method of computing the drop nucleation rate that is independent of the classical approach is also presented; the heat flux can be estimated from the nucleation rate.