Flow condensation in horizontal tubes

Abstract

This study examines condensation heat transfer in horizontal channels. Two separate condensation modules are tested using FC-72 as condensing fluid and water as coolant. The first module is dedicated to obtaining detailed heat transfer measurements of the condensing flow, and the second to video capture of the condensation film’s interfacial behavior. Four dominant flow regimes are identified: smooth-annular, wavy-annular, stratified-wavy and stratified, whose boundaries show fair agreement with published flow regime maps. The film’s interface is observed to feature an array of small ripples and relatively large waves, with the largest waves tending to merge into yet larger waves having greater liquid mass, amplitude and speed. This behavior is believed to influence condensation heat transfer, especially downstream. The local condensation heat transfer coefficient is highest near the inlet, where quality is near unity and the film thinnest, and decreases monotonically in the axial direction in response to the film thickening. This variation is very sensitive to the mass velocity of FC-72, and the heat transfer coefficient decreases sharply in the inlet region but this decrease slows significantly in the downstream region because of the combined effects of turbulence and interfacial waviness. The measured condensation heat transfer coefficient shows good agreement with a select number of correlations.