Electrohydrodynamically induced pumping and mixing of multifluid systems in microchannels

Abstract

We investigate electrostatically induced hydrodynamics in stratified flows. Vertical electric fields are used to destabilise stably stratified systems in channel geometries and generate interfacial motion. Efficient electrohydrodynamically actuated control processes are studied theoretically and shown to induce time dependent flows in small scale confined geometries without requiring an imposed velocity field or moving parts. Using linear stability theory, the most unstable wavenumbers for a given microscale geometry are identified in order to deduce electric field strengths that can be utilised to produce a required wave pattern. Starting from simple mechanisms, such as uniform field on-off protocols, promising results are presented in this context. Two-dimensional computations using the volume-of-fluid (VOF) method are conducted to fully validate the linear stability theory. Practical optimisation possibilities such as distributions of field strengths and time intervals between on and off positions are examined numerically in the nonlinear regime. We also propose a mechanism to induce pumping by generating a travelling wave voltage distribution on one or both of the electrodes. The generated flux allows for further improvement of the microfluidic mixing process and could have numerous other relevant ramifications. The analytical and numerical tools constructed enable the study of competitive alternatives in a broad spectrum of applications, from microfluidic mixing to electrostatically induced soft lithography.