EXPERIMENTAL AND COMPUTATIONAL INVESTIGATION OF PLANAR ION DRAG MICROPUMP GEOMETRICAL DESIGN PARAMETERS
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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.