Study of Condensation of Refrigerants in Micro-channels for Development of Future Compact Micro-channel Condensers

Title of Dissertation: STUDY OF CONDENSATION OF REFRIGERANTS IN MICRO-CHANNELS FOR DEVELOPMENT OF FUTURE COMPACT MICRO-CHANNEL CONDENSERS Sourav Chowdhury, Doctor of Philosophy, 2008 Directed By: Professor Michael Ohadi, Department of Mechanical Engineering Miniand microchannel technology has gained considerable ground in the recent years in industry and is favored due to its several advantages stemming from its high surface to volume ratio and high values of proof pressure it can withstand. Micro-channel technology has paved the way to development of highly compact heat exchangers with low cost and mass penalties. In the present work, the issues related to the sizing of compact micro-channel condensers have been explored. The considered designs encompass both the conventional and MEMS fabrication techniques. In case of MEMSfabricated micro-channel condenser, wet etching of the micro-channel structures, followed by bonding of two such wafers with silicon nitride layers at the interface was attempted. It was concluded that the silicon nitride bonding requires great care in terms of high degree of surface flatness and absence of roughness and also high degree of surface purity and thus cannot be recommended for mass fabrication. Following this investigation, a carefully prepared experimental setup and test micro-channel with hydraulic diameter 700 μm and aspect ratio 7:1 was fabricated and overall heat transfer and pressure drop aspects of two condensing refrigerants, R134a and R245fa were studied at a variety of test conditions. To the best of author’s knowledge, so far no data has been reported in the