Magnetically assisted liquid-solid fluidization in a gradient magnetic field : Theory and application Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/pn89d905c

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  • Development of efficient methods for the destruction of solid wastes and recovery of valuable resources is needed to support long-duration manned missions in space. In particular, these technologies are required for deployment in hypogravity and microgravity environments, such as at the lunar or Martian surfaces. Gradient Magnetically Assisted Fluidized Bed (G-MAFB) technology is under development in this study to serve as an operating platform for fluidized bed operations in the space environments. The G-MAFB technology has been specifically tailored for microgravity, hypogravity and variable gravity operating conditions. In addition, this study also focuses on the feasibility of the G-MAFB operation as a renewable filter used in the solid waste destruction process. The fluid dynamic behavior of the G-MAFB in a non-uniform magnetic field is experimentally observed in this study. The magnetic field is designed to have a stronger field intensity at the bottom of the bed, and gradually decreases toward the top of the bed. The magnetic field gradient is kept constant throughout the bed. This change in the magnetic field strength along the fluidization column varies the magnitude of the magnetic force, Fm, from the bottom to the top of the column. As a result, the particle holdup, or inversely the bed voidage, at any location varies along the column to reflect the equilibrium of all the forces involved (drag force, gravitational force, buoyancy force, and magnetic force). These experimental investigations covering four different magnetic field gradients, (dHz/dz-=-14,663 A/m/m, -18,289 A/m/m, 20,543 A/m/m and 33,798 A/m/m) and three different fluid flow rates (U₀= 0.0176 m/s, 0.0199 m/s and 0.0222 m/s) have revealed that increases in magnetic field gradient and magnetic field intensity result in the decrease in height of the fluidized bed, and therefore, in the decrease of bed voidage. The experimentally observed dynamic pressure drop ΔPf(d) is measured, and then converted to the bed voidage. A Two- Continuum Phase (TCP) method mathematical model, based on the equations of motion and the equations of continuity for both liquid and solid phases, is developed with the help of Discrete Particle Method (DPM) algorithms to theoretically evaluate the voidage distribution in the G-MAFB. Experimentally obtained bed voidage data in both, laboratory experiments (1g) and on board of the NASA KC-135 aircraft (0g) indicate good agreement with the proposed model. As part of an effort to apply the G-MAFB in the solid waste destruction process in a closed-loop life support system, a series of filtration experiments is conducted using the G-MAFB with a fixed magnetic field gradient of -38,817 A/m/m and the flow velocities varying between 0.0054 and 0.0134 m/s. The biomass waste particles suspended in an aqueous stream are recirculated between a holding tank and the G-MAFB, and the particulate concentration in the holding tank is monitored by changes in optical density of the suspension. A mathematical model describing the filtration of micron-sized solid waste particles from a liquid stream is developed. The experimental data are in good agreement with the model predictions.
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