Date of Award

10-31-1993

Document Type

Thesis

Degree Name

Master of Science in Chemical Engineering - (M.S.)

Department

Chemical Engineering, Chemistry and Environmental Science

First Advisor

Piero M. Armenante

Second Advisor

Basil Baltzis

Third Advisor

Demetri P. Petrides

Abstract

A number of studies have been published in the literature on the determination of the agitation intensity at which two immiscible liquids become completely dispersed in mechanically agitated vessels. However, no information is currently available on the agitation intensity required for the complete dispersion of two liquids in the presence of an additional gas phase. Therefore, the main objective of this study was to experimentally determine the minimum agitation speed for complete liquid-liquid dispersion, Ncd, in liquid-liquid-gas systems as a function of gas flow rate, impeller type, impeller size, and impeller off-bottom clearance. The minimum agitation speed was first determined visually. In order to eliminate the ambiguity of the visual determination method, a novel observer-free method was developed. This method is based on the analysis of the content of dispersed phase in samples taken from the mixture at different agitation speeds. The results indicate that the values of Ncd obtained with the proposed method are in close agreement (within 4%) with those obtained visually. The minimum agitation speed, Ncd, was found to be strongly affected by the air sparging rate. Higher agitation speeds were required to attain the complete dispersion state at higher air sparging rates. Ncd, was also found to be strongly affected by impeller type, impeller size, and impeller clearance for both gassed and ungassed systems.

A mathematical model based on Kolmogoroffs theory of isotropic turbulence was developed to predict the results obtained experimentally under gassed conditions. Provided that the impeller was not flooded, good agreement was found between the experimental values of Ncd, and the corresponding values predicted by the model.

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