Performance Characterization of a Traveling-Wave Electrohydrodynamic Micropump

Microscale fluidic manipulation using traveling-wave, induction electrohydrodynamics is demonstrated. A three-phase traveling-wave device fabricated for the experiments provides a temporally and spatially varying electric field which helps induce ions in a fluid subject to a temperature gradient. These ions are moved as the traveling wave propagates, resulting in a drag force being exerted on the surrounding fluid. Repulsiontype electrohydrodynamic flow is visualized in a microchannel of depth 50 μm, and results are presented in terms of velocity measurements using particle image velocimetry. INTRODUCTION Microfluidics as a means to facilitate the transfer of heat and mass, as well as varied driving mechanisms for microfluidic flows, have received much attention in recent years [1, 2]. Microchannels have gained acceptance in the thermal community as a viable option for electronics cooling [3, 4]. Reduction of package size, weight and cost while maintaining high heat transfer coefficients for removal of increasing power densities have been the driving concerns. Significant attention has also been given to use of fluids to transport biological materials [5]. Portability, disposability, cost, and sample and reagent volume reduction have been compelling reasons for the use of microdevices for biological materials handling. Micropumping solutions are an important research area to facilitate broader use of microfluidics. Among the different methods of flow actuation, electrohydrodynamics (EHD) has been used to effectively exploit the existing temperature gradient in thermal systems for flow generation. Although EHD has been studied for many years [6-10], it has more recently emerged as a potential micropump driving mechanism due to its miniaturization potential [11, 12]. Traveling-wave, induction EHD is one method of flow actuation in which a gradient in the electrical properties of the fluid is established through the depth of the microchannel in response to a thermal gradient. Ions are induced near the electrode boundary that relax in time but can be manipulated with a traveling-wave voltage boundary condition. Repulsion-type induction EHD occurs when the applied heat and traveling wave are on the same side of the channel and results in the fluid being repulsed in a direction opposite to that of the traveling wave (Figure 1). As opposed to the more common method of electroosmosis in silica-based channels, EHD does not require a charged surface resulting from spontaneous deprotonation. Further, existing temperature gradients present in cooling applications can be exploited to produce the EHD driving force. Heat Flux Increasing Electrical Conductivity Temperature Gradient Sinusoidal Potential Velocity Profile Channel walls