|Abstract:||An experimental study of friction and heat transfer characteristics for single-phase
flow in microchannel condenser tubes was conducted. Data were collected for the
adiabatic flow of nitrogen, and also for the diabatic flow of single-phase R134a w.ith air
in cross-flow. The nitrogen data were analyzed to obtain friction factors in the Reynolds
number range of 500-20000, and the R134a data were analyzed to obtain Nusselt
numbers 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 critical
Reynolds numbers for the noncircular tubes are all smaller than the value of 2100 found
for the circular-port tube. In the turbulent regime, microchannel tube friction. factors
follow a correlation for smooth tubes given by Churchill. Accordingly, there is no
evidence of surface roughness or small length scale effects. Finally, Nusselt numbers
in the range of 10000-70000, obtained from superheated vapor data, are within 10% of
the correlation given by Gnielinski. The heat transfer data in the range of 1000-7000,
obtained from subcooled liquid, are inconclusive.