Correlation of mean drop size and minimum drop size with the turbulence energy dissipation and the flow in an agitated tank

摘要

Previous correlations have focused on the relationship between the mean drop size and the physical properties of the fluids (interfacial tension, density and viscosity), the volume fraction of the dispersed phase and the average power input per unit mass of fluids. This investigation relates the mean drop size to both the maximum turbulence energy dissipation rate and the turbulent how in an agitated tank. Four impellers with varying diameters and clearances were used. The maximum turbulence energy dissipation rate was first estimated in the continuous phase (water) using a laser Doppler anemometer (LDA). Then the dispersed phase (silicone oil) was introduced. Drop sizes were measured using a phase Doppler particle analyzer (PDPA). Examination of the smallest drops showed that use of the Kolmogoroff length scale (eta = (nu(3)/epsilon)(1/4)) to estimate the minimum drop.size in liquid-liquid dispersions is not accurate. In some cases, more than 30% of the droplets have diameters smaller than the Kolmogoroff length; It was found that the mean drop size is better correlated to the maximum turbulence energy dissipation rate than to either the average power input per unit mass of fluids, or the tip speed of the impeller. Scale-up of liquid-liquid dispersions can be improved when; both the energy dissipation and the flow are considered (C) 1998 Elsevier Science Ltd. All rights reserved. [References: 43]