A Study of MHD-Induced Mixing in Microfluidics Using CFD Simulations

A comprehensive study of a two dimensional MHD (magnetohydrodynamics) micro stirrer with different electrode configurations covering a wide parameter space has been conducted by using computational fluid dynamics simulations. The wall of the circular cavity stirrer acts as the counter electrode. Cylindrical rods ranging in number from one to four, placed inside the cavity act as working electrodes. When two fluids are placed initially in the two halves of the cavity separated by an axial plane, the periodic flow reversal causes stretching, folding and breaking of the interface between the two fluids; an increase in the interfacial area; and enhanced mixing. Parametric studies conducted by varying the time period of the potential difference and the magnitude of the magnetic field intensity show that both significantly influence mixing quality. By having more complex geometries by increasing the number of working electrodes and choosing their locations inside the cavity, and by implementing specific switching schemes for the potential difference on the electrode pairs, secondary flows could be generated which introduced complex chaotic advection and enhanced mixing compared to the configuration with a single working electrode. This work adds to the relatively small body of work that relies on numerical simulations to study MHD microfluidic mixing problems. It also establishes numerical simulations as a tool for optimal design of MHD-based lab-on-a-chip applications.