An Experimental Study of Impinging Synthetic Jets for Heat Transfer Augmentation

Abstract

According to recent trends in the field of miniature electronics, the need for compact cooling solutions compatible with very thin profiles and small footprint areas is inevitable. Impinging synthetic jets are recognized as a promising technique for cooling miniature surfaces like laptops, tablets, smart phones and slim TV systems. Effect of jet to cooled surface spacing is crucial in cooling performance as well as predicting Nusselt number for such spacing. An experimental study has been performed to investigate the cooling performance of two different synthetic jets actuated with piezoelectric actuators cooling over a vertical surface. Results showed that a major degradation of heat transfer when jets are close to the surface is occurred. Slot synthetic jets showed a better performance in terms of coefficient of performance (COP) than semi-confined circular jets for small jet to surface spacing. Later, a correlation is proposed for predicting Nu number for a semi-confined circular synthetic jet accounting the effects of Re number ([Formula: see text]), jet-to-surface spacing ([Formula: see text] and [Formula: see text]) and the stroke length ([Formula: see text] and [Formula: see text]). It is found that correlation can provide predictions with an [Formula: see text] value of over 98%.

An investigation into flow and heat transfer of an ultrasonic micro-blower device for electronics cooling applications

“…Fig. 3 shows the test fixture, which is described in detail in previous publications [2,10]. The jet is placed on a traverse, which is used to fix its position to micron-scale accuracy.…”

“…Ideally, thermal management solution should be economical, low volume, and localized on the powered devices. Fortunately, some recent advances in synthetic jet devices [1,2] may provide a potential solution in both air and liquids cooling.…”

“…Unlike traditional impingement cooling, the jet is supplied by ambient fluid, as opposed to an additional coolant. Newer actuators also have more compact structures [2], potentially reducing volume further.…”

“…Early studies with pulsating jets increased convection by a factor of four [3,4], while later piezoelectric devices produced similar performance in a smaller planform [5]. Improved actuator structures led to higher jet speeds, leading to heat transfer enhancement by 10-15 times [2,6,7]. Most synthetic jets have used circular exits, while a recent design by Ghaffari et al [2] applied a slot jet with an aspect ratio of 8:1 and a rectangular cross section.…”

“…Improved actuator structures led to higher jet speeds, leading to heat transfer enhancement by 10-15 times [2,6,7]. Most synthetic jets have used circular exits, while a recent design by Ghaffari et al [2] applied a slot jet with an aspect ratio of 8:1 and a rectangular cross section. In addition, the driving piezoelectric disk was aligned in-line with the jet axis, resulting in high speeds while remaining at a compact size.…”