Vapor shear and pressure gradient effects during filmwise condensation from a flowing vapor onto a sphere

Abstract

A well-established extension to Nusselt-Rohsenow theory has been used by many investigators to model laminar filmwise condensation from quiescent pure vapors onto isothermal bodies. However, when there is a vapor velocity, shear at the liquid-vapor interface and pressure gradient effects can be important. Although these effects have been studied for some geometries (flat plates and circular cylinders), they have not been studied for the general axisymmetric case. The purpose of this work is to summarize an earlier analysis of condensation from flowing vapors onto axisymmetric bodies and report new experimental results. The experiment employed flowing trichlorotrifluorethane (CFC 113) vapor, which condensed onto a copper sphere. The apparatus, procedures, and data interpretation are discussed, and heat transfer results are compared to a correlation derived from the analytical approach. After correcting for the use of the asymptotic shear approximation, the theory underpredicts the experimental results by about 15%. However, these results do confirm the general utility of the approach and are the first reported for this geometry. It is conjectured that surface waves and boundary layer separation may be responsible for the underprediction. A correlation for practical use is proposed for condensation from a flowing vapor onto a sphere.