Introduction

Synthetic Jet Systems For Fan Augmentation for Localized Spot Cooling, Server Cooling, and Computer Server Rack Cooling

The rise in power dissipation levels of microprocessors accompanied by a shrinking thermal budget has resulted in the need for advanced server cooling technologies. The most common method of improving air-side heat transfer has been to use larger and more efficient fans driving higher flow rates. Since the power dissipation requirements have necessitated placing fans closer to the heat sink, the associated noise levels due to the flow-structure interaction have become an issue. Also, while fans are capable of supplying ample volume flow rate, they may be hindered by long-term reliability.

Fan based cooling systems are relatively inefficient in terms of the heat removed at a given volume flow rate. Air-jets typically have higher heat transfer coefficients and thermal effectiveness, but conventional air-jets are not very useful for consumer products, due to requirements of pressure supplies and conduits for directing the jets to the heat sink. Synthetic jets systems, unlike conventional jets, require no mass addition to the system, and thus provide means of efficiently directing airflow across a heated surface.

Abstract

Paper Examines Localized Spot Cooling Using Synthetic Jet Systems For Server Cooling.

This paper focuses on an implementation of synthetic jet ejectors for enhancing existing fan performance by controlling the bypass flow and imparting additional momentum to the flow. Wind tunnel tests are used to characterize the performance of an array of localized synthetic jet systems cooling two high density heat sinks in the presence of varying mean flows. The increased flow rate and heat dissipation due to the jets is measured. Results show that the percentage improvement in spot cooling due to the SynJets depends strongly on the relative flow rates of the SynJet and the mean flow. A NEWISYS server chassis was retrofitted with a synthetic jet module such that no changes to the mechanicals of the chassis were necessary. Two AMD processors in the server were stressed for high heat dissipation.

It is shown that operating a synthetic jet in conjunction with a fan enables higher heat dissipation due to localized spot cooling by the synthetic jets without impeding the flow of the fan. The high momentum SynJets enable the entrainment of significantly higher flows and heat dissipation through the heat sink than the fan alone. It is also shown the adding the SynJets enables a reduction in fan RPM for equivalent thermal performance, thus resulting in significant reduction in the sound pressure levels.

Applications

Server Cooling and Computer Server Rack Cooling

Fans alone cannot meet server microprocessor and computer server rack cooling needs. Synthetic jet systems provide fan augmentation to optimize localized spot cooling.

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