Heat transfer mechanisms in an impinging synthetic jet for a small jet-to-surface spacing

Abstract

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.

Heat transfer and air temperature measurements of an impinging synthetic air jet

“…Beyond this distance however the ambient air re-circulates and therefore a significant increase in air temperature is experienced. This is consistent with PIV flow measurements presented by McGuinn et al [22] and Valiorgue et al [10]. This does not occur at larger values of H/D as the slug flow no longer impinges directly on the heated surface.…”

“…This does not occur for the synthetic air jet at the lower value of H/D tested but is observed at the higher value of H/D = 6 as indicated in figure 3(a). For similar stroke length, Re = 1020 and H/D = 2, Valiorgue et al [10] show a small secondary peak around r/D = 3, although this study applies a constant wall flux boundary condition. By comparison with particle image velocimetry (PIV) measurements, the peak location coincides with the point where the vortex loses coherence and dissipates into turbulence.…”

“…A previous study by the authors [10], Valiorgue] has shown that the ratio of stroke length to nozzle-to-surface spacing L 0 /H determines different flow regimes and heat transfer mechanisms in impinging synthetic jets for low jet-to-surface spacing. A critical ratio of L 0 /H = 2.5 has been identified for H/D = 2, although this critical value is thought to be slightly dependent on H/D.…”

“…Kercher et al [1] investigated the applicability of miniaturized synthetic jet technology to the area of thermal management of microelectronic devices and directly compared the cooling performance of these microjets with standard cooling fans. Gillespie et al [4] investigated the effects of a small-scale, rectangular synthetic jet on the local convective heat transfer from a heated surface and also measured the velocity field between the jet orifice and the target plate [10,11].…”

Flow regime characterisation of an impinging axisymmetric synthetic jet

“…Valiorgue et al [8] and Smith and Glezer [9], however only Valiorgue et al [8] It has been shown for impinging continuous jets how turbulent mixing of the flow can enhance heat surface transfer [10]. Since the nature of the synthetic jet flow is highly transient, it is reasonable to infer that its turbulent characteristics may depend not only on Reynolds number, but also on stroke length.…”