Flow of a ferrofluid down a tube in an oscillating magnetic field

The magnetoviscosity of a ferrofluid flowing down a circular tube in the presence of a magnetic field oscillating in the direction of the axis is studied on the basis of ferrohydrodynamics, Maxwell's equations of magnetostatics, and a relaxation equation for the magnetization. Three different relaxation equations, proposed in the literature, are considered. For large amplitude of the oscillating field the three equations lead to different values of the magnetoviscosity. For large magnetic permeability the self-consistent magnetic field generated by the magnetization has significant effect.