Membrane-driven flow

Here is our poster on driving flows with metal-coated membranes in AC electric fields from the 2018 APS DFD conference. It is a recap of group alum Dr. Jaz Beharic’s membrane pumping work with newer results on the flow rate. (Related video). Such membranes could potentially drive flows in lab-on-a-chip devices or when stacked to build up more pressure, drive robotic actuators. The poster discusses bulk measurements of pressure and flow rate, but the small diameter of the pores (0.4 to 3 micron), combined with the through-surface flow orientation, makes it challenging to visualize the flow structure in a microscope using tracer particles. Particle image velocimetry can map out streamlines, vortices and “dead zones” where the fluid doesn’t move very fast. As in most AC electrokinetic experiments, the simplest version of the theory explains the direction but overpredicts the flow velocity by a lot (a factor of 4 to 20). Close-up images of these flow patterns have given researchers a chance to compare experiments with computer simulations and improve the results. Fortunately, we have seen the effect at larger pore diameters (video here) and others have managed to get side-view images of tracer particles at a different kind of membrane, so it should be possible to get streamlines that can show what’s going on here in more detail.