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Air jet impingement is one of the effective cooling techniques employed in micro-electronic industry. To enhance the heat transfer performance, a cooling system with air jet impingement on a finned heat sink is evaluated via the computational fluid dynamics method. A 2-D confined slot air impinging jet on a finned flat plate is modeled. The numerical model is validated by comparison of the computed Nusselt number distribution on the impingement target with published experimental results. The flow characteristics and heat transfer performance of jet impingement on both of smooth and finned heat sinks are compared. It is observed that jet impingement over finned target plate improves the cooling performance significantly. A dimensionless heat transfer enhancement factor is introduced to quantify the effect of jet flow Reynolds number on the finned surface. The effect of rectangular fin dimensions on impingement heat transfer rate is discussed in order to optimize the cooling system. Also, the computed flow and thermal fields of the air impingement system are examined to explore the physical mechanisms for heat transfer enhancement.

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A numerical study has been made to examine the thermal fields of rectangular impinging jets with different duty cycle(DC), which is defined as the ratio of pulse cycle on-time to off cycle time in one period, inlet Reynolds number and frequency. The Nusselt numbers show best enhancement with DC=1:3, Re=22000 and f=40Hz. The possible reason for this is that the instantaneous velocity change in this case from off to on and on to off, especially when the velocity changes from on to off, is more severe than other cases.