Experimental investigation of condensation heat transfer in microchannels.

Abstract

The thesis describes experiments aimed at measurement of heat-transfer coefficients for condensation in a multi micro channel tube. Experiments were performed with steam and R113, fluids chosen to cover a wide range of thermophysical properties, in particular, surface tension which plays an important role during condensation in small, non-circular channels. The aluminum extruded condenser tube used had cooled length 748 mm and 13 parallel channels each with height 1.38 mm and width 1.41 mm. The upper and lower outer surfaces were cooled separately by water in counter flow in channels above and below the test tube. The mass flow rates in the two channels were adjusted to be the same. Coolant temperatures were measured at 17 positions along each of the coolant channels as well as at inlet and exit. An accurate direct measurement of the overall inlet-to-outlet coolant temperature difference was also measured directly with a 10 junction thermopile for each of the two coolant streams with junctions downstream of mixers. Temperatures of the condenser tube wall were measured at 10 positions on each of the upper and lower surfaces using embedded thermocouples. Temperatures and pressures of the vapour were measured in chambers at the inlet and outlet of vapour stream. Pressures were also measured in the condenser channels just upstream and just downstream of the cooled section. Data have been obtained for cases where the vapour was saturated (for both steam and R113) at inlet. Runs were made for complete and incomplete condensation within the tube. Earlier investigations are critically reviewed and seen to exhibit wide scatter and disagreement. For reasons which will become clear in the thesis, the present results cannot, unfortunately, be claimed to have superior accuracy and generally fall within the ranges of earlier data. A new and innovative test section has been designed and will be used in forthcoming experiments.