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Umi-Umd-2588.Pdf ABSTRACT Title of Dissertation: EXPERIMENTAL AND COMPUTATIONAL INVESTIGATION OF PLANAR ION DRAG MICROPUMP GEOMETRICAL DESIGN PARAMETERS Vytenis Benetis, Doctor of Philosophy, 2005 Dissertation directed by: Professor Michael Ohadi Department of Mechanical Engineering To deal with increasing heat fluxes in electronic devices and sensors, innovative new thermal management systems are needed. Proper cooling is essential to increasing reliability, operating speeds, and signal-to-noise ratio. This can be achieved only with precise spatial and temporal temperature control. In addition, miniaturization of electric circuits in sensors and detectors limits the size of the associated cooling systems, thereby posing an added challenge. An innovative answer to the problem is to employ an electrohydrodynamic (EHD) pumping mechanism to remove heat from precise locations in a strictly controlled fashion. This can potentially be achieved by micro-cooling loops with micro-EHD pumps. Such pumps are easily manufactured using conventional microfabrication batch technologies. The present work investigates ion drag pumping for applications in reliable and cost effective EHD micropumps for spot cooling. The study examines the development, fabrication, and operation of micropumps under static and dynamic conditions. An optimization study is performed using the experimental data from the micropump prototype tests, and a numerical model is built using finite element methods. Many factors were involved in the optimization of the micropump design. A thorough analysis was performed of the major performance-controlling variables: electrode and inter-electrode pair spacing, electrode thickness and shape, and flow channel height. Electrode spacing was varied from 10 µm to 200 µm and channel heights from 50 µm to 500 µm. Also, degradation of the electrodes under the influence of an intense electric field was addressed. This design factor, though important in the reliability of EHD micropumps, has received little attention in the scientific and industrial applications literature. Experimental tests were conducted with prototype micropumps using the electronic liquid HFE7100 (3M®). Flow rates of up to 15 ml/min under 15 mW power consumption and static pumping heads up to 750 Pa were achieved. Such performance values are acceptable for some electronic cooling applications, where small but precise temperature gradients are required. EXPERIMENTAL AND COMPUTATIONAL INVESTIGATION OF PLANAR ION DRAG MICROPUMP GEOMETRICAL DESIGN PARAMETERS by Vytenis Benetis Dissertation submitted to the Faculty of the Graduate School of the University of Maryland, College Park in partial fulfillment of the requirements for the degree of Doctor of Philosophy 2005 Advisory Committee: Professor Michael Ohadi, Chair/Advisor Associate Professor Elisabeth Smela, Co-advisor Associate Professor Jungho Kim Professor Ugo Piomelli Professor Gary A. Pertmer ©Copyright by Vytenis Benetis 2005 ii Dedicated to Lina, my lifetime friend iii Acknowledgements First and foremost I would like to thank my advisor Dr. Michael Ohadi, who has put enormous faith and trust in me. He never stopped encouraging and guiding me during the entire length of my studies and research. I would also like to thank my co-advisor, Dr. Elisabeth Smela, for her continuous advice not only in her specialty area of MEMS but also for her guidance on the path of researcher (and extensive help with the final thesis). I also extend my appreciation to the other members of my advisory committee who have constantly provided constructive advice and guidance, Dr. Jungho Kim and Dr. Gary A. Pertmer. Especially I would like to thank another advisory committee member, Dr. Ugo Piomelli for his continuous support not only in the academic but also in many of the daily challenges associated with the life as a foreign student in the US. During the course of my research, I had the privilege of working with and being advised by several fellow scientists, including Dr. Jafar Darabi, Dr. Francis Franca, Dr. John Lawler, Dr. Serguei Dessiatoun and Dr. Jianwei Qi, to whom I wish to express my sincere gratitude. I am grateful to my many friends and colleagues at the Smart and Small Thermal Systems (S 2 TS) Laboratory for providing a stimulating, constructive and fun environment in which I learned and grew. I am especially thankful to Amir Shooshtari, Parisa Foroughi, Sourav Chowdhury, Guohua Kuang, Saeed Moghaddam, Arman Molki, Mihai Catalin Rada, Valentin Tudor, Jianlin Wu, Mohamed Al-Shehhi and Ebrahim Al- Hajri. iv I also wish to thank the AHX/EHD Consortium and ATEC Inc. for their long and invaluable financial support of this project. My dear parents have always supported me during the years of academic pursuits in the foreign countries. Their patience, love and care have provided me the strength to work harder and not to give up under the times of difficulties. For all of that I would like to send them my dearest thanks. Finally, I would like to express gratitude to my dearest friend Lina whom I dedicated this work to, and who had appeared in my life during this research, and helped me daily with her unmatched love and care. v TABLE OF CONTENTS LIST OF TABLES ..................................................................................................................................... IX NOMENCLATURE................................................................................................................................... XI CHAPTER 1 INTRODUCTION..................................................................................................................1 1.1 BACKGROUND...............................................................................................................................1 1.2 RESEARCH OBJECTIVES .................................................................................................................3 1.3 RESEARCH SEQUENCE ...................................................................................................................3 CHAPTER 2 FUNDAMENTALS OF ELECTROHYDRODYNAMIC (EHD) PUMPING PHENOMENA ..............................................................................................................................................7 2.1 INTRODUCTION .............................................................................................................................7 2.2 ELECTROHYDRODYNAMICS PUMPING FUNDAMENTALS.................................................................7 2.2.1 Electrohydrodynamics (EHD) definition.................................................................................7 2.2.2 Electric body forces.................................................................................................................8 2.3 GOVERNING EQUATIONS .............................................................................................................10 2.3.1 Electrical equations...............................................................................................................10 2.3.2 Fluid flow equations..............................................................................................................13 2.3.3 Nondimensional form of the governing equations.................................................................14 2.3.4 Application equations............................................................................................................15 2.4 ELECTRIC CHARGE BEHAVIOR IN THE EHD PHENOMENON..........................................................17 2.4.1 Charge generation in liquids.................................................................................................17 2.4.2 Polar and non-polar liquids ..................................................................................................18 2.4.3 Current density - electric field characteristic curve..............................................................18 2.4.4 Ion mobility............................................................................................................................20 2.4.5 Charge decay.........................................................................................................................21 2.4.6 Space charge limited current.................................................................................................23 2.4.7 Summary................................................................................................................................24 vi 2.5 LITERATURE REVIEW ..................................................................................................................25 2.5.1 Ion-drag pumps .....................................................................................................................25 2.5.2 Other EHD pumps .................................................................................................................36 2.6 SUMMARY...................................................................................................................................39 CHAPTER 3 ION DRAG MICROPUMP DESIGN, FABRICATION, AND TESTING.....................41 3.1 INTRODUCTION ...........................................................................................................................41 3.2 MICROPUMP DESIGN ...................................................................................................................42 3.2.1 Fabrication method and material selection...........................................................................44
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