Ferrofluid induced-field effects in inhomogeneous porous media under linear-gradient dc magnetic fields

Numerical simulations of ferrofluid flows through porous media with low column-to-grain diameter ratios are obtained for fluids experiencing external linear-gradient magnetic fields, ferrofluid self-consistent demagnetizing field and induced magnetic field in the non-magnetic granular phase. Analysis of the macroscopic volume-average ferrohydrodynamic model identified the conditions for decoupling magnetostatics from hydrodynamics. Order-of-magnitude calculations of the applied magnetic field versus the self-consistent demagnetizing field and the corresponding Kelvin body force densities showed that such decoupling is fulfilled only for large and positive gradient magnetic field.