Novel method for the experimental determination of the minimum agitation speed for complete liquid-liquid dispersion in agitated liquid-liquid-gas systems

A method was developed to determine the minimum agitation speed, N_cdg, for complete liquid-liquid dispersion in mechanically agitated liquid-liquid mixtures sparged with an additional gas phase. This method is an extension to three-phase liquid-liquid-gas mixtures of a method previously derived for two-phase liquid-liquid systems. The proposed 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 N_cdg so obtained and those obtained using the visual method. Additionally, the results of this study indicate that the proposed method is independent of the position of the sampling point as well as other variables, such as air sparging rate, and type, size and off-bottom clearance of the impeller. This indicates that no isokinetic sampling is required for the method to correctly derive N_cdg from the experimental data.