FREE AND FORCED-CONVECTION LAMINAR-FILM CONDENSATION ON HORIZONTAL ELLIPTIC TUBES

Laminar film condensation on a horizontal elliptical tube in a pure sa turated vapor was analyzed for conditions of Free and forced convectio n. For free convection, a simple Nusselt type analysis was used. For f orced convection, estimation of the interfacial shear stress was made in two ways: the first used an asymptotic value of the shear stress un der conditions of infinite condensation rate and the second was based on simultaneously solving the two-phase vapor boundary-layer and conde nsate equations. Effects of surface tension and pressure gradient in t he condensate film were also included. For free convection, an ellipti cal tube with the major axis vertical showed an improvement of nearly 11% in the mean heat-transfer coefficient when compared to a circular tube of equivalent surface area. For forced convection with the same a pproach velocity as for a circular tube, a small decrease (approximate to 2%) in the mean heat-transfer coefficient resulted. However, for t he same pressure drop, heat transfer performance for an elliptical tub e increased by up to 16%. (C) 1997 Elsevier Science Ltd.