Torque measurements in spin-up flow of ferrofluids

Measurements of magnetic-field-induced torque in applied uniform rotating magnetic fields are presented and compared to theoretical analyses for water- and oil-based ferrofluids. These experiments measure the viscous torque on the inner wall of a stationary, hollow polycarbonate spindle that is completely filled with ferrofluid and attached to a viscometer functioning as a torque meter. The spindle remains stationary and is centered inside a three-phase AC 2-pole motor stator winding, creating uniform time-varying rotating magnetic fields. The viscous torque is measured as a function of magnetic field amplitude, frequency, and direction of rotation. These measurements demonstrate that ferrofluid flow and torque art present even in the absence of free surfaces and agree with a recently derived analysis of the torque during spin-up flow of ferrofluids.