Prediction of electrokinetic and pressure flow in a microchannel T-junction

Abstract

It is generally accepted that in simple microchannel flows the electrical double layer at walls is thin enough for “slip velocity” boundary conditions to be used with good approximation. Recent theoretical work by one of the authors has considered the limits of this approach in cases characterized by nonuniform liquid properties and complex channel geometries. In that work, the chemically reacting flow in an arbitrary channel geometry produced by electric potential and pressure differences with heat transfer and electrophoresis is considered. The present work undertakes a broad test of the model approach in a complex channel network geometry, in the case of nonreacting uniform-property liquid. Velocity is measured by particle tracking with correction for electrophoretic motion. Measured and predicted velocities in a three-dimensional experimental T-junction within a network of five channel segments are compared for three cases of steady flow including electrically driven flow, pressure-driven flow, and mixed pressure and electrical flow. All conditions of the experiment required to determine the flow uniquely have been measured. The computational methodology used combines local three-dimensional representation with overall circuit analysis of the channel network. Comparisons are found to be within the 5% experimental scatter of the velocity measurement method used. The work emphasizes the care required in fabrication, measurement, flow control, and numerical solution if prediction of actual fabricated devices is to be achieved.