Structuring laminar flows using annular magnetohydrodynamic actuation

Laminar flow behaviour is typically observed when transporting fluids in micron-scale channels. Here, cross channel mass transport occurs only by molecular diffusion and mixing adjacent fluid streams becomes problematic. A parabolic velocity profile is also observed with pressure-driven laminar flow in a conduit. This property can be exploited by circulating fluid in an annulus such that two initially separated liquids are forced to pass through each other resulting in massive increases in the interfacial area to promote conditions for mass transfer. Miniature machined and micromachined prototypes with an integrated magnetohydrodynamic (MHD) micropump for fluid circulation were fabricated and tested. Annular MHD micromixing was characterised using fluorescein, bromophenol blue and hydrogen ion solutes for a range of velocities and modelled to include both diffusive and convective components. Furthermore, a lateral partitioning mechanism was identified and examined.