Dynamics of condensate film in the vicinity of a pulling vapor stream

Abstract

This article introduces eight possible film configurations that appear when a rising vapor stream condenses on a vertical surface. These configurations include hanging film, falling film, falling film with zero interface velocity, partly falling film, bidirectional film, partly rising film, transition film, and rising film. We develop a theoretical framework to predict condensate dynamics and heat transfer. The results show that the entire film morphology depends on a subcooling parameter (H) and a characteristic number (ϒN). Here, ϒN is the ratio of the relative Froude number and the film Reynolds number, which increases continuously from falling to rising configurations. Our analysis shows that a falling film's heat transfer and condensation rates increase as subcooling (H) increases. However, increasing H for partly falling films reduces the condensation rate, hindering the overall heat transfer. We demonstrate that the falling films produce the maximum condensate within a particular range of H; however, the maximum shifts to transition films beyond this range. As H increases, the transition films are attained at a smaller ϒN. We have identified five physical mechanisms that subtly govern the film dynamics: gravity, wall shear, interfacial shear, near wall mass-flux deficit, and interfacial mass entrainment. Concurrent participation of these mechanisms yields complex streamlines and spiral vortices.