Year

1993

Degree Name

Master of Engineering (Hons.)

Department

Department of Mechanical Engineering

Abstract

In this work a mathematical model initially developed for a counter-current bubble column gas-liquid contactor was examined. The model was developed by a lumped parameter approach to mass transfer with chemical reaction occurring completely within the liquid phase. ' An extensive literature review was carried out on gas-liquid mass transfer and in particular ozone-water mass transfer in co-current down flow. There are large gaps in the literature on this phenomenon, which indicated the need for this kind of study. The mathematical model was applied to study the behaviour of a jet pump contactor. Limited experimentation was carried out to examine some of the important characteristics of the reactor. The co-current downflow reactor was found to operate completely in annular flow with very high gas to liquid volumetric flow ratios (9 to 19). Experimental and model of determination of volumetric mass transfer coefficient revealed an extremely high value (kLa=230 sec"^), which was nearly independent of flows or flow ratios. Limited reactor flow pattern modelling, and mass transfer modelling have provided a large scope for future research. The flow pattern modelling of annular flow shows that velocities of the phases in the reactor are very high, and this leads to vastly decreased residence times. The velocities are 10 times those expected fi-om superficial velocity calculations. Modelling has shown that for the jet pump to become successful in microbiol disinfection in cooling tower water, that the residual liquid ozone concentration and/or the reactor residence time needs to be significantly increased to provide adequate CT disinfection criteria. This study has provided useful information on the jet pump, and shown that high mass transfer coefficients, high gas hold-ups and high gas to liquid flow ratios occur. The models provide a framework for further work with all hydrodynamic and chemical properties easily adjusted.

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