An experimental study of friction and heat transfer characteristics for single-phaseflow in microchannel condenser tubes was conducted. Data were collected for theadiabatic flow of nitrogen, and also for the diabatic flow of single-phase R134a w.ith airin cross-flow. The nitrogen data were analyzed to obtain friction factors in the Reynoldsnumber range of 500-20000, and the R134a data were analyzed to obtain Nusseltnumbers in the Reynolds number ranges of 1000-7000 and 10000-70000.Several types of microchannel tubes were considered, including those with circular,square, enhanced square, and equilateral triangular ports. For each tube geometry,friction factors in the laminar regime follow the known analytical solution, but the criticalReynolds numbers for the noncircular tubes are all smaller than the value of 2100 foundfor the circular-port tube. In the turbulent regime, microchannel tube friction. factorsfollow a correlation for smooth tubes given by Churchill. Accordingly, there is noevidence of surface roughness or small length scale effects. Finally, Nusselt numbersin the range of 10000-70000, obtained from superheated vapor data, are within 10% ofthe correlation given by Gnielinski. The heat transfer data in the range of 1000-7000,obtained from subcooled liquid, are inconclusive.
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