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

Abstract

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.