This manuscript has been reproduced from the microfilm master. UMI films the text directly from the original or copy submitted. Thus, some thesis and dissertation copies are in typewriter face, while others may be from any type of computer printer.The quality of this reproduction is dependent upon the quaiity of the copy submitted. Broken or indistinct print, colored or poor quality illustrations and photographs, print bleedthrough, substandard margins, and improper alignment can adversely affect reproduction.In the unlikely event that the author did not send UMI a complete manuscript and there are missing pages, these will be noted. Also, if unauthorized copyright material had to be removed, a note will indicate the deletion.Oversize materials (e.g., maps, drawings, charts) are reproduced by sectioning the original, beginning at the upper left-hand comer and continuing from left to right in equal sections with small overiaps.Photographs included in the original manuscript have been reproduced xerographically in this copy. Higher quality 6" x 9' black and white photographic prints are available for any photographs or illustrations appearing in this copy for an addittonal charge. Contact UMI directly to order. STATEMENT BY AUTHORThis dissertation has been submitted in partial fulfillment of requirements for an advanced degree at The University of Arizona and is deposited in the University Library to be made available to borrowers under rules of the Library.Brief quotations from this dissertation are allowable without special permission, provided that accurate acknowledgement of source is made. Requests for permission for extended quotation from or reproduction of this manuscript in whole or in part may be granted by the head of the major department or the Dean of the Graduate College when in his or her judgment the proposed use of the material is in the interests of scholarship. In all other instances, however, permission must be obtained from the author. SIGNED:4 ACKNOWLEDGEMENT I would like to take this opportunity to sincerely express my gratitude and appreciation to my advisor Professor Chuan F. Chen. During the entirety of studying the degree of Doctor Philosophy, he kindly provided many valuable teachings, advice, and unconditional help and support in many aspects, as like as finance, publishing two papers on the Journal of Fluid Mechanics, and very kindly correcting my disser tation writing such that the important points are evident and easy to understand. I am very grateful to Professor Thomas F. Balsa for his awarding me numerous times of Registration and Tuition Scholarship, and Graduate Fellowship. I am also thankful to Dr. Cholik Chan for his financial support.It would be impossible to complete the graduate studies without the help and support as described in above. I would like to share the honor and delight with my Ph.D. advisor. Dr. Chuan F. Chen, and the members of my comm.ttee, Dr. Thomas F. Balsa and Dr. Cholik Chan, and with my parents. I am very grateful to my parents for their love, and fait...
Air-cooled heat sinks prevail in microelectronics cooling due to their high reliability, low cost, and simplicity. But, their heat transfer performance must be enhanced if they are to compete for high-flux applications with liquid or phase-change cooling. Piezoelectrically-driven agitators and synthetic jets have been reported as good options in enhancing heat transfer of surfaces close to them. This study proposes that agitators and synthetic jets be integrated within air-cooled heat sinks to significantly raise heat transfer performance. A proposed integrated heat sink has been investigated experimentally and with CFD simulations in a single channel heat sink geometry with an agitator and two arrays of synthetic jets. The single channel unit is a precursor to a full scale, multichannel array. The agitator and the jet arrays are separately driven by three piezoelectric stacks at their individual resonant frequencies. The experiments show that the combination of the agitator and synthetic jets raises the heat transfer coefficient of the heat sink by 80%, compared with channel flow only. The 3D computations show similar enhancement and agree well with the experiments. The numerical simulations attribute the heat transfer enhancement to the additional air movement generated by the oscillatory motion of the agitator and the pulsating flow from the synthetic jets. The component studies reveal that the heat transfer enhancement by the agitator is significant on the fin side and base surfaces and the synthetic jets are most effective on the fin tips.
Convective heat transfer enhancement on a wall of a narrow channel enhanced by high-frequency, translational oscillation of a thin agitator plate is described. The oscillation is realized using a piezoelectric stack actuator. Small amplitudes of the piezoelectric stack actuator were amplified through oval loop shell structures so that large translational amplitudes are provided to the thin plate agitator. Heat transfer tests were conducted with three operating frequencies resulting from three oval loop shell structures operating at their resonance frequencies. For each operating frequency, four different amplitudes (corresponding to different applied voltages to the piezoelectric stacks) were investigated. Three channel flow rates were tested. They represent laminar, transition, and turbulent flow regimes for a non-agitated channel. Running with agitation and channel flow allows a study of the agitation effect with different channel flow rates. The results show that the oscillating plate with a frequency of about 1,140 Hz raises the convective heat transfer coefficient on the heated surface by 93%, compared to a case with channel flow only. The flow rate was 45 LPM, corresponding to the transitional flow regime in an un-agitated channel. The amplitude of oscillation was about 1.1 mm, peak-to-peak. It was found that the effect of cross flow is minimized with high oscillation frequency agitation regardless of channel flow velocity and flow regime of the un-agitated flow. In addition, numerical simulations were performed to support the experimental results and understand underlying phenomena of translational agitation. Numerical simulation results match well with the experiments and provided good explanations of heat transfer enhancement from the translational agitator. The piezoelectrically-driven oscillating agitator plate coupled with traditional fan cooling shows promising potential for advanced air cooling applications.
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