Fluid-Flow Analysis for a Novel Cylindrical Micromixer

Through computational fluid dynamics (CFD) and experiments, we studied the spiral flow and mixing process inside a novel cylindrical micromixer. Because mixing efficiency is generally poor in microflows, we expected spiral flow to enhance mixing. Parametric studies evaluated mixing efficiency in terms of flow rate and outer cylinder diameter (i.e., channel width). The patterns of streamlines and the concentration distribution obtained by CFD simulations agreed well with those obtained experimentally by flow observation and concentration measurements. Moreover, we found that the mixing efficiency was strongly influenced by the number of revolutions of the spiral flow. To predict the number of revolutions, we propose a simple equation derived by considering friction forces and angular momentum balance. Consequently, we found that when the distance between the inner and outer cylinders and/or the flow rate was increased, the number of revolutions in the spiral flow increased, which resulted in an enhanced mixing efficiency.