Body-Couple Induced Flows and Torques in Ferrofluids

Carlos Rinaldi Department of Chemical Engineering, University of Puerto Rico, MayagŸez

Suspensions of magnetic nanoparticles, commonly referred to as ferrofluids, are a commercially relevant example of structured fluids where a magnetic body couple, resulting from non-collinear local magnetic field and magnetization vectors, produces a state of asymmetric stress. Such stresses result in forces and torques on surfaces in contact with these suspensions, even in the absence of bulk flow. Alternatively, the internal angular momentum that enters the system due to the action of the magnetic body couple may be transformed into vorticity and result in bulk flow. In this talk, we will discuss measurements of the bulk flow and torques generated in a cylinder filled with ferrofluid and in the annular gap between two co-axial cylinders with a rotating magnetic field perpendicular to the cylinder axes. These torque and velocity measurements are compared to an asymptotic solution of the ferrohydrodynamic flow problem in zero spin viscosity and linear magnetization limits.

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