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 vapour 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. Results show that the entire film morphology depends on a subcooling parameter (H) and characteristic number (ΥN). Here, ΥN is the ratio of relative Froude number and film Reynolds number, which increases continuously from falling to rising configurations. Our analysis shows that 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.