Abstract
The potential of using a full shield or partial shield with a guide plate to control the bypass cooling air flowing above a heat sink is numerically modeled using two different scenarios of inlet conditions – fixed mass flow rate and specified fan curve. Excellent agreement is observed when the simulation results are compared with available experimental data in the literature. Under the first inlet condition, the Nusselt numbers associated with the full shield installation are significantly higher than those without a shield, but with a significant pressure drop penalty. Friction factor increases with partial shield height till it reaches a maximum value with the full-shield configuration. Using an inclined guide plate with a partial shield alters the flow direction, forcing the air to impinge on the heat sink. This adds an extra cooling effect but without causing a considerable increase in the friction factor. In the case of fixed inlet mass flow rate, most of the partial shield and guide plate cases show the lowest pressure drop when the ratio of the partial shield height to the total bypass height Hs/HBP is between 0.35 and 0.5. The case with an inclination angle of θP = 15° has the highest thermal performance and the highest pressure drop. Correlations for the average Nusselt number and friction factor are developed to include the effect of Reynolds number, shield height, bypass height and guide plate inclination angle. For the second inlet condition, the test cases are repeated using a selected fan characteristic curve as an alternate to the fixed mass flow rate condition. The specified fan curve case shows that a short partial shield with a slightly inclined guide plate has a better thermal performance than the full shield case. Furthermore, using a guide plate only with a small inclination angle has a superior thermal performance. Changing the position of the guide plate is investigated as well and the optimal location is obtained.
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