Residence Time Distributions in a Co-Current Electrically Enhanced Liquid–Liquid Contactor

Abstract

This paper describes an experimental study of the mixing and residence time behaviour in an electrically enhanced liquid–liquid contactor. A pair of laboratory-scale contactors were designed in which water was electrostatically sprayed co-currently into a continuous immiscible liquid phase. The residence time distribution of the continuous phase was determined using a classical pulse response technique involving injection of inert red dye into the continuous phase inlet region. Residence time distribution data were determined as a function of the electrical field applied across each contactor. The experimental data were fitted to a number of classical single and multi-parameter models in order to gauge the effect of applied field upon mixing. The classical single parameter models based on stirred-tanks-in-series and on a dispersion coefficient did not fit the data very well except at high nominal electrical field strength. A better fit was obtained using a combined model based on a single plug flow/single continuous stirred tank reactor combination with by-pass flow. Another model was developed using the advection-dispersion differential equation and this gave the best comparison with the experimental observations. In all cases the experimental observations and the conclusions from each model fitting were consistent. The model based on the advection–dispersion differential equation was also validated using an alternative geometry in the second contactor and gave an accurate description. A more rigorous approach based on continuum mechanics to predict the velocity field in the continuous phase may be considered in future, in particular to quantify the influence of dispersed charged drop motion upon continuous phase mixing.