The cooling impact of a pair of confined angled air jets impinging on a printed circuit board

The unsteady laminar flow and heat transfer characteristics for a pair of angled confined impinging air jets centered in a channel were studied numerically. The time-averaged heat transfer coefficient for a pair of heat sources centered in the channel was determined, as well as the oscillating jet frequency for the unsteady cases. The present study is a continuation of the authors\´ previous investigations, which emphasized the hydrodynamic interaction between two adjacent and parallel jets and the impact of the small heat source spacing leading to a reduction in heat transfer when increasing the flow Reynolds number in the unsteady regime. This study examines the interaction between the angled jets and the associated impact on the cooling of the heat sources placed on the board at a jet Reynolds number of 300 and 600. Maintaining the inlet jet width, W, at 1 cm, as in the previous studied cases, the interaction between the 30° angled jets leads to the formation of a single steady jet that impinges on the two heat sources placed on the board at a Reynolds number of 300. A second case investigates the hydrodynamic interaction between the 30° angled jets at a Reynolds number of 600. In this case, the jets form a single unsteady jet that sweeps the target board and the heated components placed on it. The nature of this unsteadiness depends on the proximity of the jet inlets, the channel dimensions and the jet Reynolds number. The jet unsteadiness causes the stagnation point locations to sweep back and forth over the impingement region causing the jets to "wash" a larger surface area on the target wall. A third and final case investigates 30° angled jets with inlet widths halved but with an increased velocity to maintain a Reynolds number of 600. A prior study indicated that in the range of Reynolds numbers studied a fixed stagnation "bubble" was formed on the target wall between the two jets. The "bubble" reduced the heat transfer removal from that region, leading in fact to a quasi-independence of the local heat transfer on flow conditions. In the present study, due to the peculiar interaction between the angled jets and the formation of a single jet, the "bubble" between the heat sources that previously diminished the heat transfer will- not occur. A comparison with alternative designs and their impact on the heat source thermal performance is further investigated.