Date of Award
Doctor of Philosophy
G. M. Colver
The mechanisms for controlling elutriation and bubbling effect in a fluidized bed are largely unexplored. Increased understanding of these hydrodynamic effects will help to improve both fluidized bed design and operation;In the present study, an electric field was used as an independent parameter to control the formation of bubbles and the elutriation of fines in a fluidized bed. Various forces which acted on the particles were compared. It was concluded that both the current constriction force and hydrodynamic force dominated the behavior of the bed;The bed expansion increased as much as 15% of the bed height at the incipient fluidization with the application of an electric field, as compared to an increase of only 2 to 3% without an electric field. The field significantly improved bubble control. Various parameters that influenced bubble control, included relative humidity, electric field strength, and frequency of the electric field. The effect of bed resistivity and bed temperature were also studied and correlations have been proposed relating to the above variables;Criteria for bubble control for both DC and AC electrical field models were proposed and the ratio of hydrodynamic to electric forces were calculated. The predicted effective electric field strength was in agreement with experimental data;A stability analysis for bed expansion using an elasticity modulus of the bed was also studied. The elasticity modulus at minimum bubbling condition under different situations which were determined both theoretically and experimentally. Good agreements were found between the theoretical and experimental results. Various parameters affecting the bed stability were also studied. Bubbles could easily form with a lower bed elasticity modulus. Scale-up parameters were also derived based on non-dimensional analysis.
Digital Repository @ Iowa State University, http://lib.dr.iastate.edu/
Wang, Jiun-Shen, "Bubble and elutriation control in fluidized beds with electric fields " (1995). Retrospective Theses and Dissertations. 10735.