National Science Foundation
Cooling Technologies Research Center
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CTRC Breakthroughs

Electrically Actuated Microscale Flows

Enhanced Electrohydrodynamic Micropump

MEHD pump breakthroughs figure The enhanced electrohydrodynamic micropump design consists of a traveling-wave electrode array in contact with a fluid that moves ions induced in the fluid domain with the traveling electric field. Higher phase representations of the traveling-wave (for a given wavelength), in addition to an increase in electric field strength by electrode design modifications have been shown to increase flow rate by approximately 75%. A microfabricated pump has also been completed to benchmark modeling results. A peak in the velocity has been observed at a frequency that corresponds to the charge relaxation time of an ion in the fluid. Additionally, the effect of externally applied heat to increase the temperature gradient (necessary for ion induction) has been demonstrated experimentally. A velocity increase of approximately 50% was observed with an additional 0.3 W of heat flux applied on one boundary. Using the validated numerical model, the capability of removing heat with electrohydrodynamic micropumping has been evaluated. The figures show device layout and instrumentation of an electrohydrodynamic micropump.

Electrical Control of Liquid Droplet Motion and Morphology on Smooth and Microstructured Superhydrophobic Surfaces

Electrowetting breakthroughs figure A generic modeling framework was developed to predict the electrical actuation of low electrical conductivity and insulating liquid droplets using AC and DC voltages. Detailed and careful measurements of droplet velocities (of different types of liquids) under electrical actuation were carried out in a specially designed setup. Electrowetting-induced Cassie (nonwetting) to Wenzel (wetting) transition on superhydrophobic surfaces was studied analytically and experimentally. The microscale surface design enabled the first reported direct visual confirmation of the electrowetting-induced Cassie-Wenzel transition. A careful experimental study of heat transfer due to droplet motion on a hot inclined substrate was carried out as part of the FRS project. A numerical model was developed to calculate heat transfer coefficient due to droplet motion on a single plate and droplet motion sandwiched between two plates. Dynamic contact angle and contact radius were measured experimentally for a wide range of frequencies at different AC voltages. A numerical modeling technique was developed to predict droplet retention under gravitational forces.