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Whereas the heat transfer mechanisms in steady impinging jets are well understood, the available knowledge of heat transfer to impinging synthetic jets remains inconsistent. This paper provides an objective comparison of the stagnation point heat transfer performance of axisymmetric impinging synthetic jets versus established steady jet correlations. Furthermore, a general correlation for the stagnation point Nusselt number is proposed including the effect of all appropriate scaling parameters: Reynolds number (500 ≤ Re ≤ 1500), jet-to-surface spacing (2 ≤ H/D ≤ 16) and stroke length (2 ≤ /D ≤ 40). Based on the ratio of stroke length to jet-to-surface spacing L L 0 0 /H, four heat transfer regimes are identified.

Impinging synthetic jets have been identified as a promising technique for cooling miniature surfaces like electronic packages. This study investigates the relation between the convective heat transfer characteristics and the impinging synthetic jet flow structure, for a small jet-to-surface spacing H/D = 2, dimensionless stroke length 1 < L 0 /D < 22, and Reynolds number 1000 < Re < 4300. The heat transfer measurements show evidence for a power law relationship between the Reynolds and Nusselt number for a constant stroke length. A critical stroke length L 0 /H = 2.5 has been identified. Using phase-resolved particle image velocimetry, vortex quantification is applied to elucidate the influence of the impinging vortex on the timeaveraged heat transfer distribution.

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