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Solid Suspension in Rotary-Stirred and in Liquid-Jet Stirred Vessels

Zolfagharian, Akramolmoolouk; (1990) Solid Suspension in Rotary-Stirred and in Liquid-Jet Stirred Vessels. Doctoral thesis (Ph.D), UCL (University College London). Green open access

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Experimental data are provided on the just-suspension conditions for two types of mechanically-stirred units, namely rotary-agitated vessels and liquid jet-stirred tanks. Results for the conventional rotary-stirred vessels (propellers and 4-blade 45°-pitch turbines) are presented in terms of the well-established just-suspension speed, Nje, based on the 1-2 seconds criterion. Data on the liquid-jet stirred tanks are presented as the minimum liquid jet velocity through the nozzle at the point of just suspension of particles, Uje, for a range of nozzle diameters (0.005m to 0.0127m) in five flat-bottom geometrically similar cylindrical vessels with diameter in the range 0.15m to 0.3m. Experimental data on Nje and Uje. are interpreted in terms of a new model developed in this work. The general model equation is based on a balance of the hydrodynamics and body forces acting on the particles at various states of suspension and on the energy requirements for particle suspension. The form of the final equation depends on the geometrical configuration and on the source of agitation. Two equations are developed in this work: one for Nje, and the other for Uje. These are as follows: For propellers and turbines with D/T < 0.5 and: Predictions of the effect on Nje and Uje of the various physical and geometrical parameters are in reasonable agreement with corresponding experimental data obtained in this work and those reported in the literature, with the exception of the effect of particle diameter. Limited experimental observations suggest that the effect of particle diameter on just-suspension state can not be described by a single expression over the whole range of dp, as predicted by the model equations. Data obtained in this work with rotary agitation indicate that a downward-pumping propeller with D/T < 0.5 is the most energy efficient impeller of all the agitators examined. A comparison of the propeller- and jet-stirred vessels suggests that at just-suspension conditions, the power input into a propeller is about the same as the power input into a liquid-jet stirred unit operating under otherwise identical conditions, and provided that the ratio of nozzle diameter to vessel diameter is in the range 1/20–1/25.

Type: Thesis (Doctoral)
Qualification: Ph.D
Title: Solid Suspension in Rotary-Stirred and in Liquid-Jet Stirred Vessels
Open access status: An open access version is available from UCL Discovery
Language: English
Additional information: Thesis digitised by ProQuest.
URI: https://discovery.ucl.ac.uk/id/eprint/10122127
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