As the field of microfluidics continues to grow, it is becoming increasingly important to understand the mechanisms involved with heat transfer in two-phase flow through microgeometries. This importance is reiterated by the increasing number of applications which use phase change as the principal mechanism to conduct or remove heat. The purpose of this study was to investigate fluid mechanic and heat transfer characteristics of two-phase two-component flow in rectangular microchannels. Experiments were conducted using rectangular aluminum channels with hydraulic diameters ranging between 56 μm and 256 μm and aspect ratios which varied from 0.5 to 1.5. Both single- and two-phase tests yielded excellent correlations of the friction factor. Reynolds number and the combination of Reynolds number and Prandtl number were the dominant parameters in the prediction of pressure drop and heat transfer rate, respectively. The pressure drop predictions, based on available semi-empirical relations for two-phase flows, were shown to substantially over predict the measured pressure drop.

Other findings showed that for single-phase flow, the transition from laminar to turbulent regimes of the friction factor was suppressed as the channel hydraulic diameter decreased. Two-phase friction factor data indicated a definite transition from laminar to turbulent regimes at a Reynolds number of 3,000 for all channel configurations tested. It is believed that the transition was due to the intense pressure fluctuations associated with two-phase flows. In both single- and two-phase experiments, Nusselt number data exhibited a trend similar to the macroscale turbulent regime correlations; however, the data were somewhat less than the macroscale predictions. In contrast to the friction factor data, both single- and two-phase Nusselt number data suggested no change in flow regimes occurred.

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