Heat- and mass-transfer analysis for the condensing film flow along a vertical grooved tube

A three-dimensional heat-transfer analysis procedure for the coupled conden sing/evaporating films flowing down along the outer/inner walls of a vertic al grooved tube has been developed. It is quite complex as many important s olution elements such as the free-surface tracking, the conjugate heat tran sfer, and the phase change, need to be carefully incorporated. To effective ly treat the condensing flow along the grooved outer wall, where the free-s urface location is yet to be determined, a general nonorthogonal moving gri d technique is employed. Given the vapor properties on both sides, the full y elliptic Navier-Stokes and energy equations are solved for the temperatur e and velocity fields by using a SIMPLE-type finite volume method. The anal ysis is successful in capturing the free-surface location along with the am ount of condensate and other major three-dimensional characteristics. Most of the condensation is seen to take place on the bare portion of the groove surface and that clearly demonstrates how the heat transfer is enhanced by the grooved surface. The results are presented for various groove densitie s and operating conditions. The optimum groove number appears to vary with the temperature difference of the two sides. The effect of the surface tens ion is also discussed. (C) 2001 Elsevier Science Ltd. All rights reserved.