An experimental study on fully developed laminar flow and heat transfer in rectangular microchannels

An empirical study has been performed to explore the validity of theoretical correlations based on conventional sized channels for predicting fluid flow and heat transfer characteristics in microchannels. The flow resistance and thermal behavior of laminar flow through 10 different rectangular microchannels with hydraulic diameters of 155-580 µm and aspect ratios of 0.25-3.8 at Reynolds numbers ranging from 30 to 2500 were investigated. The single-phase laminar friction factors in the microchannels conformed to the conventional Poiseuille flow theory. The critical Reynolds number increased from 1700 to 2400 with a decrease in the aspect ratio from 1.0 to 0.25. The existence of two heat transfer regimes was verified. At Re< 180, the experimental Nusselt numbers were lower than the theoretical values and increased rapidly with the Reynolds number. The Nusselt numbers began to exceed the theoretical values for Re> 180; however, its rate of increase with the Reynolds number slowed considerably. In this region, the theoretical value of the Nusselt number was assessed to be reasonable as an estimate for rectangular microchannels when the aspect ratio was greater than 1.0.