Date of Award
1990
Degree Type
Dissertation
Degree Name
Doctor of Philosophy
Abstract
Entrainment is an important consideration in the design of gas-solid fluidized beds. Particle fluxes are typically measured by a movable cone in the freeboard zone which samples the total gas-solid flow or pseudo-isokinetic sampling probes which measure local fluxes. A comparison of measurements obtained with these two methods is needed to reconcile data obtained in various scale equipment. The ability to predict entrainment flux and particle size distribution is crucial for modelling freeboard reactions and specifying equipment to control particle losses.;Coning and pseudo-isokinetic sampling were used to measure solids upflux for fine sand (d{dollar}\sb{lcub}\rm p{rcub}{dollar} = 80 {dollar}\mu{dollar}m), fluidized in an 0.61 m diameter fluidized bed at several superficial gas velocities. A novel probe was used to sample the local solids downflux. Sufficient air entered the probe to match the velocity at the probe exit with the superficial velocity and convey the sampled particles to the recovery system.;The total upflux measured with these two techniques was similar although the Sauter mean diameter above the TDH was lower for the coning technique. Fractional flux profiles revealed that the rapidly changing contour of the cone had de-entrained coarser particles.;Entrainment flux data is determined with constant percentage error indicating that weighted least squares fitting is appropriate. The precision of the parameter estimates improved when this approach was adopted.;An inverse height power law model provided the best fit of experimental upflux data. Independent confirmation of the superiority of this model was offered by the close agreement between measured downflux and downflux computed from a freeboard mass balance and the fitted upflux equation.;The experimentally observed entrainment profiles can be described as the sum of a height dependent cluster flux with the same size distribution as the bed material and a non-cluster flux which is constant throughout the freeboard.;Further development of this analysis revealed that an exponential distribution of bubble sizes at the bed surface leads to the exponential decay law that is in common use. A model based on a log-normal distribution of bubbles provided improved agreement with experimental data.
Recommended Citation
Hazlett, John David, "Entrainment From Gas-solid Fluidized Beds (volumes I And Ii)" (1990). Digitized Theses. 1884.
https://ir.lib.uwo.ca/digitizedtheses/1884