Proceedings of IMECE2006: 2006 ASME International Mechanical Engineering Congress and Exposition November 5-10, 2006, Chicago, Illinois, USA DRAFT IMECE2006-13264 ENHANCED ELECTROHYDRODYNAMIC PUMPING AT THE MICROSCALE Lorenzo Cremaschi, Brian D. Iverson and Suresh V. Garimella Cooling Technologies Research Center School of Mechanical Engineering Purdue University West Lafayette, Indiana 47907-2088 USA (765) 494-5621; sureshg@ecn.purdue.edu ABSTRACT An enhanced electrohydrodynamic micropump for use in small-scale liquid pumping applications is developed. The micropump can be incorporated into an integrated circuit chip to provide active cooling. Liquid flow is achieved by combining two actuation mechanisms: electrohydrodynamics (EHD) and the action of a vibrating diaphragm. Heat generated by active devices creates a thermal gradient in the fluid allowing induction of ions to be driven by EHD. The vibrating diaphragm enhances the EHD efficiency allowing more pumping power to be transferred to the fluid. The design and operation of the micropump are discussed, and results are presented in terms of volume flow rates. INTRODUCTION Thermal management of electronic components is of increasing concern in the development of portable and reliable electronic devices. The need to reduce package weight and volume while increasing the functionality has received much attention in recent years. The reduction in transistor size and the increase in power density necessitate alternative cooling techniques to replace conventional air-cooled heat sinks. Liquid cooling provides a path to achieving higher heat removal rates, but has been limited by the requirement of large pumps to drive the flow. Micropumping solutions are thus an important research area to facilitate broader use of liquid cooling. A recent review of possible micropumping mechanisms is available in [1]. Although EHD has been studied for many years [2-6], it has recently emerged as a potential micropump driving mechanism due to its miniaturization potential [7, 8]. Combining two promising scalable pumping mechanisms – EHD with nozzle-diffuser elements and vibrating diaphragm actuation – Singhal and Garimella devised a micropump with the potential for direct integration into an active chip for heat removal [9]. Subsequent investigations led to a straight channel design (without converging/diverging elements) in which the EHD pumping mechanism is enhanced by the fluid motion from the diaphragm vibration [10, 11]. Building on these concepts, the present work describes the design and operation of a 1 cm × 1 cm enhanced EHD micropump. DEVICE DESIGN AND OPERATION A wide, straight channel design (similar to [10]) has been employed to simplify the fabrication. The channel is 8 mm wide by 10 mm long, with a 50 μm depth. The channel design incorporates a 54.7° side-wall angle typical of KOH chemical wet etching. Electrodes are patterned on the inside upper surface of the channel and cover the entire width and length of the channel upper wall. In order to capitalize on the scaling benefits resulting in a stronger electric field for EHD, an array of 6 μm wide electrodes and 12 μm spacing was considered. Every third electrode was connected to one phase of a 3-phase traveling potential (f = 122 kHz) wave with magnitude 200 V to induce ions in the fluid. A temperature difference of 10 K is established across the depth of the channel where the low temperature side corresponds to the top wall with electrodes. Thus, a gradient in the electrical properties of the fluid is established along the depth of the microchannel. The coldest fluid, which has low electrical conductivity, is closer to the electrodes, which is the region with the most intense electrical field in the microchannel. Such an orientation results in attraction-type induction EHD and the fluid follows the traveling potential wave in the same direction. The fluid properties used are the same as in Singhal and Garimella [9]. The piezoelectric patch covers the entire platform area of the pump such that the entire channel top wall vibrates with the piezo actuation at frequency of 10 kHz. Fabrication of this device is currently underway. The basic transport equations (mass, momentum, and energy) that govern the flow were solved using a finite element method in a numerical model employed to simulate the 1 Copyright © 2006 by ASME