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Abstract
Condensation in microchannels has applications in a wide variety of advanced microthermal devices. Presented here is a review of both experimental and theoretical analyses of condensation in these microchannels, with special attention given to the effects of channel diameter and surface conditions on the flow regimes of condensing flows occurring in these channels. This review suggests that surface tension, rather than body or buoyancy forces, is the dominant force that governs the condensation and two-phase flow in these microchannels. Recent experimental results indicate that with decreases in the channel diameter, the dominant condensing flow pattern is intermittent injection/slug/bubble flow, as opposed to stratified or annular flow, which is typically found in two-phase flows in larger one-g channel flows. As a result, existing annular flow condensation models cannot be used to accurately represent or predict the actual physical mechanisms that occur in these condensing flows in microchannels. This therefore necessitates the use of semitheoretical models or correlations based upon experimental data. Since wettability and surface roughness play an important role in the condensing flow in microchannels, an optimization of these effects may provide a mechanism by which very high condensation heat fluxes can be achieved.
The authors gratefully acknowledge the support provided by the NASA, the Key Project of the Chinese Ministry of Education No. 105082, Fok Ying Tung Young Teacher Education Foundation No.101055, and Outstanding Young Teacher Foundation at Southeast University. The partial support of this work by Natural National Science Foundation of China through grant No. 50536010 is also gratefully acknowledged.