A new method for heat transfer coefficient measurements of single-phase fluids during laminar flow in microchannels

The measurement of heat transfer coefficients in microchannels is complicated due to the small sizes involved. Moreover, a heat transfer mechanism which is not usually considered, the axial conduction effect in the channel wall, must also be evaluated in micro-scale measurements. Previous heat transfer coefficient measurements have not accounted for the axial conduction effect, and those measurements showed the inconsistent result with the theory. In this paper, a new measurement method is developed to validate the theory that predicts a Nusselt number independent of Reynolds number in the laminar flow regime for microchannels. A numerical model is used to simulate heat transfer characteristics in a microchannel with wall conduction, and to predict the wall temperature difference between a location at the end of the heater and a location 3 mm away from the heater on the microchannel. The temperature difference is experimentally measured on a 160 mu m hydraulic diameter microchannel and compared with the numerical model. The comparison shows that the Nusselt number in the laminar flow regime for the microchannel is independent of Reynolds number at least down to Re=300. (C) 2020 Elsevier Ltd. All rights reserved.