Ferrofluid surface and volume flows in uniform rotating magnetic fields

摘要: Ferrofluid surface and volume effects in uniform dc rotating magnetic fields are studied. Theory corroborating measurements presented for meniscus shapes resulting driven flows, spin-up Hele-Shaw cell flows instabilities. To characterize the water-based oil-based ferrofluids used experiments, were made of magnetization curve, tension, viscosity, density, speed sound. Extensive height shape ferrofluid menisci applied show that increases vertical fields, whereas horizontal decrease height. An approximate energy minimization analysis agrees with observed trends The curvature on flow modeled under simplified assumptions. Analytical solutions derived two dimensional low Reynolds number extended results obtained numerically using COMSOL's Multiphysics finite element software package (FEMLAB) to solve three recirculating at higher numbers. Familiar magnetostatic expressions linear media non-linear relations. These study instabilities cells simultaneously in-plane axial fields. Ultrasound velocimetry bulk region conclusively demonstrates co-rotation field without a free surface. Careful ultrasound investigation profiles different heights uncovered cylinders showed direction reversal between counter-rotating top co-rotating ferrofluid. A framework numerical solution coupled governing equations conservation angular momentum considers all terms first Shliomis relaxation equation was formulated solved. Previous literature which decouple fluid mechanical dynamics by neglecting spin velocities result no absence diffusion effects. Contrary commonly held view literature, develop even Including velocity non-zero flow. Numerical FEMLAB shown zero viscosity. Fitting simulations profile allows estimation time viscosity Ferrotec Corp.'s MSG W11 EMG705 ferrofluids. (Copies available exclusively from MIT Libraries, Rm. 14-0551, Cambridge, MA 02139-4307. Ph. 617-253-5668; Fax 617-253-1690.)