Among the few assumptions that Nusselt made in deriving his widely used equation for the condensate film heat transfer coefficient was the one which stated that the condensate film offers the only resistance to the heat transfer. Thİs means that the effect of the vapour pbase on the heat. transfer is negligible and that the surface temparature of the condensate is equal to the saturation temperature of condensing vapour. However, there are practical situations where this assumption is not valid in which case one has to take the so-called interfacial resistance into account.