Advances in film condensation including surface tension effect in extended surface passages

Theoretical investigations of film condensation heat transfer started in 1916 by Nusselt. Initially, only the gravity and viscous force effects were taken into consideration in the condensate film, followed by the investigations of the vapor shear effect at the liquid-vapor interface. The importance of the effect of surface tension force on film condensation phenomena has been realized since 1940s (Armstrong, 1945) with the first analytical investigation by Gregorig in 1954. Surface tension drains the condensate film from the fin crest and interfin base regions into fin corner regions, thus creating thinner films and more effective condensation surfaces in these regions. On the other hand, surface tension causes the retention of the condensate in the finned tube bottom which results in a decrease of the effective heat transfer surface and in deterioration of film condensation heat transfer. The objective of this paper is to review the literature on film condensation heat transfer that emphasizes the study of surface tension and its effect on film condensation phenomena. Primary emphasis is given to condensation in extended heat transfer surfaces focusing on three fin geometries: integral-fin, longitudinal fin, and microfin tubes. The most important correlations and analytical models reported in the literature are compared and compiled in a single table. We have summarized our assessment of the influence of surface tension on condensation heat transfer in the geometries covered, and how and where it has beneficial effects. Based on this assessment, specific areas of future research for film condensation heat transfer are outlined.