STUDIES ON MULTIPHASE AGITATION

Abstract

The present study deals with the determination of minimum impeller speed for complete liquid-liquid-gas (three-phase) dispersion, Ncdg , in a mechanically agitated baffled vessel of 0.2038m i.d. using a turbine impeller. Mineral oil (diesel and kerosene) and water were used as the dispersed and continuous phases respectively. Compressed air was used as the gas phase passed through a ring sparger. Ncdg was determined visually and also by sampling method. The method is based on the analysis of the curve generated when the values of the dispersed phase fraction in samples collected from the bulk of the mixing vessel are plotted against the corresponding agitation speeds. The results of this work show an excellent agreement between the values of Ncdg so obtained and those obtained using this visual method. Additionally, the results of this study indicate that the proposed method is independent of the position of the sampling point, air sparging rate, volume fraction of dispersed phase and off-bottom clearance of the impeller. This indicates that no isokinetic sampling is required for the method to correctly derive NCd9 from the_ experimental data. It was observed that Nrdg decreases with the increase in -superficial velocity of air, in the given range. A correlation has been proposed for three-phase (liquid-liquid-gas) system for different volume fractions of dispersed phase. Nedg =K D1.97 μc/9 μd 1/9 G 0.3 ('NP) us Us — where, K= 160 andA=-0.114when4=0.1 K=208 andA=-0.074when4=0.15 Deviation between predicted and experimental values was observed to be ± 15%.