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Electronics Cooling Designs: Synthetic Jets

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Electronics Cooling Designs: Synthetic Jets

Electronics Cooling continued

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Over the past few weeks, we have looked at different types of electronics cooling and thermal management methods utilized within the electronics fields. Previous devices we discussed included, Heat Pipes, Heat Sinks, Peltier cooling plates and Electronic Fluid Accelerators. To continue the series, we examine possibly the most complex device from a fluid mechanics perspective,  known as a synthetic jet, a device that uses alternating suction and ejection to create to a high heat transfer coefficient.  While we have presented these for electronics cooling, they may be used in other applications.

How a Synthetic Jet Works

Utilizing a synthetic jet forced air method into electronics cooling is not completely new but it does have its advantages for continued development.  The ability to increase the effectiveness on air powered cooling methods is appealing due to the fact that these methods are more reliable and cost effective. By creating an extended area, or pocket, of air cooling, they allow for a higher heat transfer while maintaining lower flow rates. synthetic jets are formed by alternating suction and ejection of a fluid from a hole or vent by the motion of a diaphragm on the wall of the system. As the diaphragm makes its move down, it violently ejects a pulse of air into a heat sink. The pulse is then ejected with such high velocity that a secondary flow is generated. Once the initial pulse has been ejected, the diaphragm moves up and pulls in cool air at a much lower velocity. Over time, this repeated process creates a vortex. Once the vortex is formed, the flow is unsteady and turbulent. Turbulent flow is generally defined as the Reynold number being above 2000.  Turbulent flow may be contrasted with laminar flow. This type of flow results in a much higher heat transfer coefficient as, we discussed above, and then lower airflows are needed to cool the same amount of dissipated power. Alternatively, given the same size of device, there can be greater cooling. The use of synthetic jets as the primary jet is an attractive option because the only input is electrical and requires no plumbing or pressure supplies.  As the technology to reduce the size of jets advances, engineering firms have begun developing a two-dimensional synthetic jet. The two-dimensional jet creates a similar vortex to a conventional jet, and is achieved using piezoelectric and electromagnetic drivers, and electrostatic or mechanical driven pistons. Piezoelectric driven diaphragms hold an advantage by weighing less and using less power while electromagnetic ones tend to have better noise control and are deemed more reliable.

Thermal Management uses

The ability to locate synthetic jets for hot spot placement allows for a more direct cooling method on smaller applications. While some devices such as heat sinks require a small fan for optimal performance, the synthetic jet can replace cooling fans for devices such as microprocessors, memory chips, graphics chips, radio frequency components and high-powered LEDs.  However, when a synthetic jet is integrated with heat sinks, it allows for the heat sink to be much smaller which allows more design and engineering freedom. To decrease the noise while increasing reliability as well as lowering the thermal resistance of a synthetic jet, it can be used in conjunction with a fan.

Engineers utilize technology to further design electronics cooling

Today’s engineers make use of  the different types of tools available to them as we have discussed previously, to design and create more efficient and effective ways to improve thermal management. By using CAD to create 3D models, they can effectively create the area of conditions for testing. A licensed engineer using FEA and CFD software can then take these models and produce the test results needed to determine the feasibility of a project without having to build many prototypes, which is a major factor in cost control.[/fusion_builder_column][/fusion_builder_row][/fusion_builder_container]

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