An experimental investigation of single-phase forced convection in microchannels

Turbulent, single-phase forced convection of water in circular micro channels has been investigated Channel diameters of 0.76 mm and 1.09 mm have been used. Water inlet velocities range from 3 to 19 m/s, corresponding to Reynolds numbers of 3.2 x 10(3) to 23 x 10(4), while the Prandtl numbers range from 4.21 to 6.43. The data show that the Nusselt numbers for the 0.76 mm channel are significantly higher than those predicted by traditional large channel cor-relations, such as the Gnielinski correlation, for the same Reynolds and Prandtl numbers. This result is in agreement with earlier research for circular microchannels with considerably smaller diameters (similar to 0.102 mm). The data for the 1.09 mm diameter channel show significantly less deviation from the predicted behavior using the Gnielinski correlation, with only slight increases in the Nusselt numbers. The research provides further support for the notion that conventional correlations for turbulent single phase convection are not applicable for channels with small (submillimeter) hydraulic diameters. It also provides experimental evidence about the channel size at which the deviation becomes insignificant. Based on the data obtained in this investigation, along with earlier data for smaller diameter channels, a generalized correlation for the Nusselt number for turbulent, singlephase, forced convection in circular microchannels has been developed. The diameter Reynolds number, and Prandtl number ranges are 0.102-1.09 mm, 2.6 x 10(3)-2.3 x 10(4), and 1.53-6.43, respectively. With a confidence level of greater than 95%, differences between experimental and predicted Nusselt number values are less than +/-18.6%.