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Two component fluidization.

University of British Columbia

Studies were made of the distribution of components, when two materials are fluidized in a liquid. The hypothesis tested was that the distribution of material is a function of the bulk density difference of the component beds. The component bed having the greatest bulk density will occupy the bottom of the total bed. It is possible for the bulk density of one material to be greater than the other at low velocities, and less than the other at high velocities. At some intermediate condition the bulk density difference between the two beds must be zero. This situation, called the inversion point, produces homogeneous mixing of the two components. Mixtures of two materials for which an inversion was predicted by the stated hypothesis were tested. In the intermediate and turbulent flow regions inversions did not occur because macroscopic mixing destroyed the bulk density gradients being established. However, in the laminar flow region, where mixing was negligible, inversions did occur. The quality of the inversion was affected as follows. For a sharp clear inversion of the two materials at the predicted velocity, the diameter ratio of the two groups of particles must be much greater than one and the density ratio (corrected for buoyancy) of the two groups of particles must be much less than one. Also of importance is the absolute density (corrected for buoyancy) of the particles. Particle size distribution also appeared to strongly affect the quality of the inversion. These distributions set up balk density gradients within the single component beds. This appeared to cause mixing of the two components and in some cases even formation of the two inverted beds before the predicted inversion velocity was reached. The prediction of the bed expansion of mixtures was also studied. A correlation was developed on the assumption that each component of the mixture could be treated separately. The overall expansion thus would be the sum of the expansions of the individual components. There was very good agreement between values predicted by this method and experimental data. The method predicted expansion well for all degrees of mixing of the two components, but did not predict well when one of the components was near its minimum porosity for fluidization. The empirical equations of Richardson and Zaki (4) for single component liquid fluidization expansions were checked. The values of the index "n" Obtained from experimental data agreed within ± 5% of those calculated using the correlations. The equation developed by Richardson and Zaki for determining the free settling velocity of a single particle from extrapolated expansion data gave results which were within ± 15% of those obtained using the standard drag coefficient-Reynolds number plot for an isolated sphere.

Text

2011-10-04

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http://hdl.handle.net/2429/37772

Chemical and Biological Engineering

University of British Columbia

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