MicroPIV and micromixing study of corona wind induced microcentrifugation flows in a cylindrical cavity

Recently, a novel way of driving rapid microcentrifugation was discovered using ionic wind via ionization of the atmosphere around a singular electrode tip, driving liquid recirculation in a small cylindrical cavity due to interfacial shear. In the original work, the primary azimuthal surface recirculation was speculated to drive a secondary flow in the bulk of the liquid which resembles a helical swirling flow that tapers toward a pseudo-stagnation point at the cavity floor, analogous to Batchelor flows between co-axially placed stationary and rotating disks. Here, we employ microParticle Image Velocimetry (microPIV) together with numerical simulations to verify this speculation. Good qualitative and reasonable quantitative agreements were obtained between the experiments and numerical simulations. In both, we were able to capture salient features of the three-dimensional flow; for the experiments, this was achieved by the reconstruction of the three-dimensional flow field from the planar two-dimensional velocity fields obtained in a confocal-like manner. In addition, we formally quantify the micromixing enhancement first demonstrated, but not quantified, in the original experiments. Our results show a mixing enhancement close to two orders of magnitude approaching vigorous mixing intensities as the surface vortices suffer from various instabilities leading towards their breakdown into subvortices at large applied voltages and AC frequencies, reminiscent of that in the original work.