Abstract: We performed a transient numerical investigation on a microchannel heat sink with multiple impinging jets (MHSMIJ) to explore the effects on the fluid flow and heat transfer characteristics of the MHSMIJ of an unsteady impinging jet and heat flux imposed upon the substrate surface by using a computational fluid dynamics method. The heat fluxes being imposed upon the substrate surface and the inlet velocities of the jet were all set as sinusoidal functions with different amplitudes and periods with time. The effects of the amplitudes and periods of the functions on the substrate properties were analyzed. Cooling performance was evaluated by calculating the periodic average surface heat transfer coefficient, average temperature uniformity, and temperature variation of the target surfaces over a period. The results indicated that the surface heat transfer coefficient and average temperature of the cooled surface oscillated with the periodic heat fluxes, accompanied by obvious phase lags. The phase lag has a significant dependence on the periods, but little dependence on the amplitudes. The material properties of the substrate have complex influences on the transient behavior of the MHSMIJ. The periodic heat flux and periodic jet velocity significantly affected the transient thermal performance of the MHSMIJ, but had less effect on its overall performance. Further, transient heat flux and jet velocity caused non-uniform and transient temperature distributions, which will cause thermal fatigue phenomenon, and thereby have effect on the longevity of the MHSMIJ.

Key words: Microchannel heat sink with impinging jets, Heat transfer, Sinusoidal heat flux, Sinusoidal inlet velocity, Phase lag

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