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Title: Study of granular temperatures in gas-solid fluidized bed by diffusing-wave spectroscopy
Author: Xie, Liansong
Awarding Body: University of Edinburgh
Current Institution: University of Edinburgh
Date of Award: 2004
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Experimental investigations have been carried out on hollow glass micro-spheres with average diameter 60μm in two dimensional rectangular air-fluidized beds. The particle bulk and effective densities were 110kg/m3 and 200 kg/m3 respectively. Fluidized bed expansion and pressure drop across the bed were studied. Despite theoretically belonging to Group C (cohesive, difficult to be fluidized) according to Geldart’s powder classification, these microspheres fluidized easily and the beds expansion was extremely high when the gas velocity was increased above the minimum fluidization value. Using diffusing-wave spectroscopy (DWS), granular temperatures were determined throughout the gas fluidised bed for superficial velocities up to and somewhat beyond the minimum bubbling velocity, which was more than 4 times the minimum fluidisation velocity. The granular temperature was found to increase smoothly with superficial velocity between the minimum fluidisation and minimum bubbling velocities, contrary to the results of earlier workers who also used DWS, but consistent with the results of other workers using less direct methods. It was found that the granular temperature at a set superficial velocity increased with height above the distributor whilst the pressure gradient remained constant. This, combined with increasing laser light transmission, suggested particle clustering with the cluster size decreasing with height. Granular temperature was found to vary symmetrically about the bed centreline where it was also maximal, corresponding to velocity profiles observed by others for similar bed geometries. Preliminary studies of particle microdynamics in a laboratory scale circulating fluidized bed were also made.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available