As heat dissipation from electronic components dramatically increases due to the rapid development of integrated circuits with micro-nano fabrication, the need increases for powerful cooling facilities. Different cooling schemes such as liquid cooling, direct sprays, boiling heat transfer, etc. have been developed to meet the needs of heat removal. Air cooling still has potential for improvement and continues to hold many advantages over liquid cooling in terms of simplicity, reliability, cost, etc. Conventional heat sink systems with blowers or fans are approaching maximum thermal management capability due to dramatically increased heat dissipation from the chips of high power electronics. In order to increase thermal performance of air-cooled heat sink systems, more active or passive cooling components are continually being considered.
One technique is to agitate the flow in the heat sinks to replace or aid conventional blowers. In the present study, an active heat sink system that is coupled with a piezoelectric translational agitator and micro pin fin arrays on the heat sink surfaces is considered. The piezoelectric translational agitator generates high frequency and large displacement motion to a blade. It is driven by an oval loop shell that amplifies the small displacement of the piezo stack actuator to the several-millimeter range. Detailed vibration characteristics were studied through theoretical and experimental analyses. Dynamic operating frequency and displacement were estimated through the theoretical analysis. The blade, made of carbon fiber composite, is easily extended to a multiple-blade system without adding much mass. The micro pin fin arrays were created with the LIGA photolithography technique. The cooling performance of the heat sink system was demonstrated in single-channel and multiple-channel test facilities employing either plain or micro pin-fin surfaces. Intensive heat transfer experimental results are provided. A total Reynolds number was defined to characterize the combined effects of cross flow and agitation. The Stanton number developed from the relationship between the total Reynolds number and heat transfer coefficients enables predicting operating performance. Different configurations of the translational agitator with multiple blades were fabricated and tested in a 26-channel, full-size heat sink. The experimental results showed that the proposed active air cooling has a promising potential for the thermal management of high power electronics.
University of Minnesota Ph.D. dissertation. August 2012. Major:Mechanical Engineering. Advisors:Prof. Tianhong Cui and Prof. Terry Simon. 1 computer file (PDF); xii, 175 pages
A piezoelectric translational flow agitator for active air cooling of electronics..
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