Single phase pressure drop in microchannels

This article focuses on investigating fully developed liquid and vapor flow through rectangular microchannels with hydraulic diameters varying from 69.5 to 304.7 μm and with aspect ratios changing from 0.09 to 0.24. R134a liquid and vapor were used as the testing fluids. During the experiments, the Reynolds numbers were varied between 112 and 9180. Pressure drop data are used to characterize the friction factor in the laminar region, the transition region and the turbulent region. When the channel surface roughness was low, both the laminar friction factor and the critical Reynolds number approached the conventional values, even for the smallest channel tested. Hence, there was no indication of deviation from the Navier–Stokes flow theory for rectangular microchannels. The friction factor data in the turbulent region were larger than the predictions from the [Churchill, S.W., 1977, Friction factor equations spans all fluid-flow regimes, Chemical Engineering 45, 91–92] equation for smooth tubes, even for the smoothest channel tested (Ra/Dh = 0.14%). In addition, it was likely that surface roughness was responsible for higher laminar flow friction and earlier transition to turbulent flow in one of the channels tested.