Magnetoviscosity of Magnetic Fluids Under Oscillating and Rotating Magnetic Fields Obtained through Rotational Brownian Dynamics Simulations

The magnetic field dependent viscosity (magnetoviscosity) of dilute suspensions of magnetic spherical particles suspended in a Newtonian fluid subjected to both magnetic and shear flow fields was studied numerically. Brownian dynamics simulations were performed to compute the intrinsic magnetoviscosity of the suspension. Results are presented for the response of dilute suspensions of spherical particles to oscillating magnetic fields and magnetic fields that are co-rotating or counter-rotating with respect to the fluid vorticity. A decrease in the intrinsic magnetoviscosity is observed for oscillating and co-rotating magnetic fields. The frequency corresponding to zero viscosity and the minimum value in the negative viscosity are lower for co-rotating magnetic fields than for oscillating magnetic fields. In the case of counter-rotating magnetic field the results show a maximum in the intrinsic magnetoviscosity of the suspension. For both cases the frequency at which the viscosity achieves maximum or minimum values is dependent on the dimensionless shear rate, parameterized through the rotational Peclet number, and the dimensionless magnetic field strength, parameterized through the Langevin parameter.