Meso Scale Pulsating Jets for Electronics Cooling

Abstract

Microfluid devices are conventionally used for boundary layer control in many aerospace applications. Synthetic jets are intense small-scale turbulent jets formed from periodic entrainment and expulsion of the fluid in which they are embedded. The jets can be made to impinge upon electronic components thereby providing forced convection impingement cooling. The small size of these devices accompanied by the high exit air velocity provides an exciting opportunity to significantly reduce the size of thermal management hardware in electronics. A proprietary meso scale synthetic jet designed at GE Global Research is able to provide a maximum air velocity of 90m∕s from a 0.85 mm hydraulic diameter rectangular orifice. An experimental study for determining the cooling performance of synthetic jets was carried out by using a single jet to cool a thin foil heater. The heat transfer augmentation caused by the jets depends on several parameters, such as, driving frequency, driving voltage, jet axial distance, heater size, and heat flux. During the experiments, the operating frequency for the jets was varied between 3.4 and 5.4 kHz, while the driving voltage was varied between 50 and 90VRMS. Two different heater powers, corresponding to approximately 50 and 80 °C, were tested. A square heater with a surface area of 156mm2 was used to mimic the hot component and detailed temperature measurements were obtained with a microscopic infrared thermal imaging technique. A maximum heat transfer enhancement of approximately 10 times over natural convection was measured. The maximum measured coefficient of performance was approximately 3.25 due to the low power consumption of the synthetic jets.

Recent Developments on Synthetic Jets (Review Paper)

“…Since the turbulent contents in the flow break the thermal boundary layer and penetrate much closer to the heated surface of the devices, SJ effectiveness is much higher than the continuous flow fans. By optimising driving frequency, amplitude, jet axial distance, heater size, and heat flux 40 , it was observed that the heat transfer of SJ was increased approximately 10 times over natural convection.…”

“…It was found that the thermal effectiveness of the heat sink increased close to 70 per cent which was more than twice that of a typical fan-heat-sink combination. Garg 40 , et al developed a 0.85 mm diameter rectangular SJ actuator at GE global research which produced 90 m/s jet velocity. They found that the heat transfer increased approximately 10 times over natural convection.…”

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

“…We use a series of experimental and computational analyses to determine the conduction, natural convection, and radiation losses, using methods explained in detail earlier [2,6,10]. Conduction and natural convection losses are examined using a three-step process, initially developed by Garg et al [6].…”

“…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.…”

Cold Zone Exploration Using Position of Maximum Nusselt Number for Inclined Air Jet Cooling

“…Normally, jets are established by pressurizing the fluid. Air jet produced by compressed air, water jet produced by water pump, but synthetic jets uses electromagnetic principle (by which micro-jets are produced) [16,17]. The structural exit cross-section of the jet gives varied flow patterns of the jet, which has an effect on cooling ability.…”