Modelling Annular Micromixers

Magnetohydrodynamic mixing of two fluids in an annular microchannel is modelled as a twodimensional, laminar, convection-diffusion problem, and examined using asymptotic analysis and numerical simulation. The time T required for mixing of a plug of solute depends on the Peclét number Pe, and on the geometry of the annulus. Three scaling regimes are identified: purely diffusive, Taylordispersive, and convection-dominated; each with a characteristic power-law dependence of T upon Pe. Consequences of these results for optimal micromixer design are discussed.