Displacements of miscible magnetic fluids in a capillary tube

Displacements of miscible magnetic fluids in a capillary tube under a moving ring-shaped magnet are studied numerically. The magnet is adjusted dynamically to maintain a constant distance from the mixing tip on the centerline. Control parameters, such as magnetic pulling force, effective viscosity variation due to magnetization and the position of the magnet, are analyzed systematically. Mass transfer performance is evaluated by several quantitative measurements. In general, a stronger magnetic effect leads to a better performance, except for the global amount of transferred mass that varies insignificantly. An asymptotic tip velocity is reached if the magnetic strength is beyond a certain value. A less effective viscosity leads to a higher finger velocity but a shorter transferable distance. Unlike the monotonic influences of magnetic pulling force and effective viscosity variation, there exists a potential optimal magnet position for the best effective mass transfer.