Unsteady state measurements of oxygen dissolution rates in water were carried out in a large baffled aerated mixing vessel (0.6 m8 capacity) at various gas flow rates and agitator power inputs for a variety of impeller types. A mathematical model accounting for the gas and liquid phase dynamics was formulated to evaluate the mass transfer product ()La). Measurements of the dispersion bubble properties (diameter, interfacial area and gas bold-up) were also made and correlation, for gas hold-up, interfacial area and aerated power dissipation were proposed. It is believed that valid values of kLa have been determined for the air-water system, using a correct mathematical model; most of the earlier studies using physical methods, reported in the literature, have made several unjustified assumptions in determining kLa. The order of merit of several different agitators in regard to effective use of power for gas-liquid mass transfer was established and a new type (the comb turbine) was found to be superior, under certain circumstances, to the conventionally used "Rushton turbine". The effect of scale-up on kLa in aerated mixing vessels was also experimentally examined by carrying out some experiments in a geometrically similar smaller tank (0.049 m). A deterioration in mass transfer rate is found on scale-up at constant power per unit volume of liquid and constant superficial gas velocity, but further work is required to establish the causes.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:649247 |
| Date | January 1978 |
| Creators | De Figueiredo, Maria Margarida Lopes |
| Publisher | University of Edinburgh |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://hdl.handle.net/1842/13600 |
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