Single-phase convective heat transfer performance of wavy microchannels in macro geometry

The feasibility of attaining microscale heat transfer effects using macro geometries has been demonstrated. The concentric superposition of two macro geometries, manufactured through conventional machining, yielded an annular microchannel with a microscale gap of 300 μm. In this paper, sinusoidal wave geometrical profiles were introduced on the inner cylinder's surface to enhance convective heat transfer and the overall energy efficiency, for a given heat transfer area. Experimental and numerical studies were conducted on steady-state, single-phase heat transfer, using distilled water as the coolant, with an operating Reynolds number range of 1300-4600. Results showed that the enhanced microchannels with higher wave amplitudes and shorter wavelengths performed better in terms of heat transfer, at the expense of heightened pressure losses. Overall, the highest-performing enhanced microchannel is capable of removing 51 percent more heat than the plain annular channel at a given pumping power. In addition, large wave amplitudes coupled with low operating Reynolds number yielded optimal heat transfer efficiency and vice versa. The wavy profiles promote heat transfer efficiency through flow perturbation and the reinitialization of boundary layers along the peaks while keeping pressure losses relatively low. New correlations for the average Nusselt number and friction factor were proposed for the wavy annular microchannels, which can be utilised for future compact heat exchanger designs, exhibiting enhanced microscale heat removal capabilities while employing relatively economical fabrication processes.