The prediction of voidage distribution in a non-uniform magnetically assisted fluidized bed : theory and experiment Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/0v838321q

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  • Previous studies in Magnetically Stabilized Fluidized Bed (MSFB) are well known for conventional two-phase, gas-solid or liquid-solid fluidization. Many researchers have investigated the fluid dynamic behavior of the MSFB, however, all of these studies are based on a uniform magnetic field that is constant throughout the bed column. Currently, there are no references in the open literature indicating either fundamental or applied research with a magnetically fluidized bed where a non-uniform magnetic field is used in a two-phase liquid-solid fluidization. In this study, the fluid dynamic behavior of a Magnetically Assisted Fluidized Bed (MAFB) in a non-uniform magnetic field is experimentally observed. In the MAFB, a magnetic force, F[sub m] , is created which acts on the ferromagnetic particles (20% ferrite) by varying the magnetic field intensity from the top to the bottom of the fluidization column. However, the field gradient is kept constant throughout the bed. Because of the differences in the magnetic field intensity at any location in the bed, the particle holdup, or inversely the bed voidage, has to change to accommodate the equilibrium of forces acting on the particles (drag force, gravitational force, buoyancy force, and magnetic force). In the laboratory experiments, performed magnetic field gradient, [see PDf for equation] Alm/m, -18,289 Alm/m, -20,543 Alm/m and -33,798 A/m/m) and fluid flow rate (U[sub 0] =0.0153 m/s, 0.0176 m/s, 0.0199 m/s and 0.0222 m/s) are varied. These experiments show that the increase in the magnetic field gradient and the magnetic field intensity results in the decrease in the height of the bed, and therefore, in the decrease of the bed voidage. The dynamic pressure drop, [delta]P[sub f][sub(d)], is also experimentally measured, then converted to a corresponding voidage. The relationship between the dynamic pressure drop and the bed voidage is given by the following equation:[see PDF for equation] The fluid dynamic behavior of the MAFB is described by the equation of motion and the equation of continuity for both liquid and solid phases. A mathematical model is developed and used to evaluate the voidage distribution in the MAFB. The resulting expression for the voidage distribution in the MAFB is given as [see PDF for equation]. Experimentally obtained bed voidage data in both, laboratory experiments (1g) and on board of the NASA KC-135 plane (0g) fit very well the above equation which does not have any adjustable parameter.
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