Surface tension-affected laminar film condensation problems

Abstract

Following Nusselt [1] there were few developments in the theory of laminar film condensation until the advent of digital computers in the 1950s. Approximations used by Nusselt, namely neglect of inertia, convection and surface shear stress (for the free convection case) were then found to give very accurate results for the normal practical range of vapour-to-surface temperature difference. Subsequent developments treated the gas phase and dealt with superheated vapour, condensation in the presence of a non-condensing gas and condensation of mixtures. The temperature discontinuity at the vapour-liquid interface has been studied experimentally and theoretically since the 19 th century and more recently in the 1960s by experiments using liquid metals.In the present paper the focus is on the condensate film and, in particular, the role played by surface tension which is important for condensation on finned surfaces and in microchannels, owing to abrupt changes in curvature of the condensing surface. The way in which surface tension affects condensation heat transfer and difficulties which arise are first illustrated by reference to condensation on a smooth horizontal tube, where the effect of surface tension on heat transfer is minimal. Practically more relevant cases of condensation in microchannels and on finned surfaces and are then discussed and recent results presented.