The objective of this effort is to pursue artificial microscale surface roughness features in the form of dimples, on the walls of an air-cooled heat sink channel, as a passive option to energy-efficiently augment heat transfer in forced convection flows. High fidelity numerical simulations were employed for realizing an optimized dimple configuration and to comprehend the behavior of microsized dimples under high velocity (∼17 m/s) transitional flow conditions. Fully developed flow simulations were performed, and design of experiments with response surface methodology was employed for the numerical optimization. The results showed ∼30% heat transfer improvement and ∼15% pressure drop increase in the fully developed region compared to a smooth-walled channel. Practicability of manufacturing 200 μm deep dimples on a 600 μm thin aluminum fin was demonstrated. Experiments were also carried out to assess the performance of the aforementioned optimized configuration in a custom built setup in the laboratory, which showed up to 10.5% heat transfer improvement and ∼12% pressure drop increase over a corresponding smooth-walled channel. The above results indicate that the performance of dimples is allied with the flow development characteristics. In addition, experiments performed at Reynolds numbers other than one at which the dimples were optimized showed inferior performance showing that application-specific optimization of dimples is crucial. With further exploration of shape and design parameters, dimples might have the potential to improve thermal performance passively and form an attractive candidate to realize high-performance air-cooled heat sinks in the future.

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