Experimental studies on steam condensation in horizontal and vertical microtubes

Abstract

Microchannels have increasingly been used in the industry to miniaturize heat transfer equipment, improve energy efficiency, and minimize heat transfer fluid inventory. A fundamental understanding about condensation in microscale will yield far reaching benefits for the automotive and HVAC&R industries. In this study, the effect of microchannel diameter and orientation on condensation heat transfer is investigated. Steam is used as the working fluid, microtubes with inner diameters of 500 and 900 μm inner diameters, in horizontal and vertical orientations were used. The working fluid was pumped into the vapor generator from the reservoir after passing through a micro- filter. Saturated vapor was generated via electrical heating and was then led into the condensing section. Flow condensation occurred in the microtubes. The condensate leaving from the outlet of the condensing section was cooled in the cooler before flowing through the micro flow-meter. It was found that the condensation heat transfer coefficient increased with mass flux, heat flux, and vapor quality, while pressure drop increased with the mass flux and vapor quality. At low mass fluxes, it was found that the channel orientation had a considerable effect on heat transfer coefficient, while this difference diminished as mass flux increased. As mass velocity increased, differences in heat transfer coefficient are reduced.