Zhiyuan Shen

Date of Award


Degree Type


Degree Name

Doctor of Philosophy


Downward gas jets can be found in many important process fluidized bed reactors, but design and operation data are scarce in the literature. The need for an understanding of such reactors led to a study, for this project, of hydrodynamics and mass transfer of a single downward air jet in a 2D fluidized bed of sand particles.;The jet issuing from a downward nozzle shifted between the two sides of the nozzle through a cyclic sequence of left-central-right-central-left positions. While the jet flowed along one side of the nozzle, a small fraction of the nozzle air split out to the other side and formed satellite bubbles rising through the bed. The jet cycling time was a random variable which could be described by a log-normal probability distribution. Its average reached a minimum at the aspect ratio 1.58. Both the increase in the jet velocity and the presence of internals had an increasing effect on the average jet cycling time. A proposed wave model interpreted that the jet cyclic motion was caused by the sloshing of the fluidized bed. This was supported by the fact that the cyclic motion was in synchronism with the change in the pressure difference between the two sides of a nozzle. A lower pressure was found on the side of the jet flow and a higher pressure on the side of satellite bubbles.;The jet also fluctuated in width and there was no fixed position for the jet boundary. This led to a successful approach using the concept of the jet presence probability. The gas dispersion coefficient from the nozzle gas zone to the emulsion phase was further determined from tracer experiments. It increased with the jet velocity and was about one fifth of that reported in the literature for upward jets.



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