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Improving Cooling System Acoustics, Power and Reliability Using Synjets for Fan Augmentation
Keywords: SynJets, Fan Augmentation, System Power Acoustics Reliability
Synjets have been shown to be very effective in control of mean flows in aerodynamic flow control applications. A similar principle can be applied to flow bypass control, where Synjets are used for controlling a fan induced flow passing over a heat sink. Adding an array of Synjets upstream of the inlet to the heat sink enables controlled re-entrainment of the inlet flow to reduce flow bypass while simultaneously breaking up the local boundary layers on the walls of the heat sink. To test the efficacy of this methodology, a Synjet assembly was retrofitted into a commercially available 4300 quad-socket, 3U, rack-mounted model server. Due to the space constraints and PCB layout within the server, two of the processors have reduced-height heat sinks, which conform to a 1U form factor, and two of the processors have full-height 3U heat sinks. The Synjet was located directly in front of these shorter heat sinks without modifying the existing server chassis architecture. The case to ambient thermal resistance of one of the CPU's with and without the jet augmentation at different fan speeds was measured. The inlet velocities vary in the range of 550 to 750LFM over the range of fan speeds. At the idling speed of 5500 RPM the thermal resistance drops from about 0.43 C/W to about 0.35 C/W, while at the full speed of 9000 RPM, the performance goes from 0.325 to 0.302 C/W. By operating the fans at lower speed, the SPL of the system dropped by about 9dBA and cooling power consumption was reduced from 108 to 62W. The addition of SynJets improves overall system reliability by enabling reduced fan speeds, thus reducing wear of mechanical fan components, the rate at which airborne contaminants foul the system and the fan.
Raghav Mahalingam, Chief Scientist
Austin, TX

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