Use of high gradient magnetic fields for separation of macromolecules

High gradient magnetic field separation has been used in such diverse applications as separation of ore tailings, red blood cells, and sewage. The majority of studies have been carried out using a single ferromagnetic wire or a wire mesh to produce the field gradient necessary for particle capture. Most of these cases involved the capture of ferromagnetic or paramagnetic entities. Few studies have addressed the interactions of diamagnetic particles with single ferromagnetic spheres or columns packed with spheres. In this thesis, particle trajectory equations have been extended to include effects of particle charge on capture of paramagnetic and diamagnetic particles by ferromagnetic spheres. In addition, magnetic field and field-gradient behavior have been examined for two closely placed spheres in order to ascertain possible effects of close-sphere-packing in columns on particle capture. The effect of particle charge can be quantified by a dimensionless group (E) which is proportional to the particle charge and background magnetic field and inversely proportional to fluid viscosity and particle radius. Magnetic field strengths were varied from 3 to 50 tesla while utilizing both parallel and perpendicular magnetic field-fluid flow orientations. Both field-flow geometries yielded similar results. Interaction between charge and the magnetic field increases the time required for capture as the value of E approaches unity. The increase for the perpendicular case was substantially larger than the parallel case because the magnitude of the cross product between magnetic field and flow streamlines is much larger. Addition of an electrical charge term leads to a possible particle stagnation point for the perpendicular case, located several particle diameters away from the surface of the ferromagnetic sphere. The effect of two closely spaced spheres was quantified by looking at the absolute value of the magnetic field and magnetic force term for several sphere spacings. It was found that the maximum values of the magnetic field and force term were larger than that for a single sphere. Also the magnetic force term is larger over the entire surface of the sphere. In a packed bed of spheres the distance between spheres is minimized so with the enhanced magnetic field and force terms the capture of particles could be enhanced in a packed bed.