Charged droplet and particle-mixing studies in liquid-liquid systems in the presence of non-linear electrical fields

This paper is concerned with the mixing and residence time distribution behaviour of an experimental electrically enhanced column contactor in which electrically charged drops of water were fed into an organic liquid phase of sunflower oil across which a non-linear electrical field was maintained. The effects of electrical field strength upon mixing in the continuous phase were determined and a significant increase in mixing was observed as the field strength was increased. A quantitative theoretical development describing the observed behaviour is also presented. The mixing is described by simultaneous consideration of the movement of the drop phase and the continuous liquid phase. The drop motion, after formation at the charged nozzle and during the subsequent trajectory motion under the influence of the non-linear electric field, is analysed. The interaction between the drop motion and the velocity field of the continuous phase is thus described. The paper describes theoretical prediction of the interactions between charged drops and the electrodes. These interactions can exert a strong influence on the overall residence time of drops passing through the column, and potentially on the velocity profile of the continuous phase. Description of both sets of interactions is used to predict mixing patterns in the continuous phase as a function of applied field strength. The predicted mixing patterns are compared with experimentally recorded images of tracer movement in the continuous phase obtained under the same conditions. The calculated patterns compare favourably with those measured by experiment. The modelling methodology was used afterwards with success for predicting the residence time distribution in the form of the normalised concentration (proportional to the exit function) versus time.