Simple models and measurements of magnetically induced heating effects in ferromagnetic fluids

This paper discusses several approximate analytic techniques for calculating power dissipation and forces in ferromagnetic fluids subjected to a spatially uniform but time varying magnetic field. This power dissipation results in a rising temperature in a ferrofluid sample. Several possible heating mechanisms in magnetic fluids have been investigated, including electromagnetic and hydrodynamic processes, and a simple method for prediction of power dissipation in a sample has been developed. Experimental results are given for an induction heating problem where it is shown that the power dissipation in a sample of ferrofluid cannot be explained by induction heating of the individual suspended particles. A simple viscous drag model is introduced which shows better agreement with measured power dissipation in the sample than an eddy current model for excitation frequencies under 1 MHz.