The paper reports calculations of friction pressure gradient for the special case of laminar annular flow condensation in microchannels. This is the only flow regime permitting theoretical solution without having recourse to experimental data. Comparisons are made with correlations based on experimental data for R134a. The correlations differ somewhat among themselves with the ratio of highest to lowest predicted friction pressure gradient typically around 1.4 and nearer to unity at high quality. The friction pressure gradients given by the laminar annular flow solutions are in fair agreement with the correlations at high quality and lower than the correlations at lower quality. Attention is drawn to the fact that the friction pressure gradient cannot be directly observed and its evaluation from measurements requires estimation of the nondissipative momentum or acceleration pressure gradient. Methods used to estimate the nondissipative pressure gradient require quality and void fraction together with equations which relate these and whose accuracy is difficult to quantify. Quality and void fraction can be readily found from the laminar annular flow solutions. Significant differences are found between these and values from approximate equations.
Pressure Drop During Condensation in Microchannels
Mile End Road,
London E1 4NS, UK;
Institute of Engineering Thermophysics,
Chinese Academy of Science,
Contributed by the Heat Transfer Division of ASME for publication in the Journal of Heat Transfer. Manuscript received June 26, 2012; final manuscript received January 26, 2013; published online July 26, 2013. Guest Editors: G. P. “Bud” Peterson and Zhuomin Zhang.
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Wang, H. S., Sun, J., and Rose, J. W. (July 26, 2013). "Pressure Drop During Condensation in Microchannels." ASME. J. Heat Transfer. September 2013; 135(9): 091602. https://doi.org/10.1115/1.4024465
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