Department: Mechanical & Aerospace Engineering
Faculty Advisor(s): Robert J. Cattolica

Primary Student
Name: Kevin Matthew Mandich
Email: kmandich@ucsd.edu
Phone: 858-534-2433
Grad Year: 2013

A temporal linear stability analysis is performed by introducing a three-dimensional disturbance into the continuum-averaged equations of motion for the fluid and dispersed particle phases which constitute a uniform fluidized bed. An additional mechanical energy conservation equation for the particle phase accounts for the spatiotemporal variation of particle velocity fluctuations, otherwise known as the granular temperature. The stability characteristics of the system are investigated at various combinations of fluidized bed parameters to obtain practical results. Findings include how a certain particle density or diameter yields the least stable flow for each combination of parameters. It is also shown that the disturbance frequency of the least stable mode approaches a constant as the fluidization velocity is increased, and that it generally drops as the voidage decreases. Results indicate that a 2D disturbance is always less stable than its 3D counterpart, and is sufficient to describe such a system. The new instability mechanisms are analyzed and compared to those from previous isothermal stability investigations. It is found that the growth constant generally increases with the base-state granular temperature field. The least stable mode is found to be purely transverse, although the vertical mode dominates in the limit of small wavenumbers. A large vertical wavelength expansion is performed on the simplified, one-dimensional analogue of the dispersion relation. One of the new mechanisms is found to dominate the flow stability over a large range of the solid volume concentration.

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