Magnetofluidic spreading in circular chambers under a uniform magnetic field

Elucidating the microscale interaction between magnetism and fluid flow is of great importance for designing micro-magnetofluidic gradient generators, micromixers, and particle sorters. Co-flowing magnetic and non-magnetic fluids can lead to instability at their interface and subsequent rapid mixing. The mismatch in the magnetisation of the fluids leads to instabilities. The present study systematically investigates the magnetofluidic spreading phenomena of both magnetic nanoparticles and non-magnetic fluorescent dye in consecutive circular chambers. Numerical simulations and experimental investigations were conducted to thoroughly evaluate the physics of magnetofluidic spreading. We show that the presence of the consecutive chambers can enhance magnetofluidic spreading by slowing down the flow and increasing the mass transfer rate transversal to the flow direction. The numerical results reveal that the magnetic force, induced by the magnetic susceptibility gradient, generates cross-sectional secondary flows that steer particles toward both the top and bottom walls. The induced secondary flow also enhances the transport of fluorescent dye, thereby leading to a higher mass transfer rate as compared to pure molecular diffusion. The findings provide further insights into the microscale spreading phenomenon of magnetic and non-magnetic particles in a magnetic field.