(543b) Motion of Charged Drops in a Non-Newtonian Liquid-Liquid System

The design of liquid-liquid contacting equipment requires knowledge of drop size and distribution in order that rate equations can be formulated. The context here is intensive liquid-liquid contacting in which the dispersion of an aqueous phase into a solvent phase is achieved by electrostatic spraying. An electrical charge is placed upon drops as they emerge from a nozzle into an immiscible second liquid phase. This is achieved by connecting the nozzle to a high tension electrical source and simultaneously placing an electrical field across the continuous phase. The drops move under the influence of the field and may be accelerated. The advantages of electrostatic dispersion include significant reduction in drop size, enhancement of mass transfer, and enhanced rates of phase separation. The reduction in drop size can be very significant and is one of the principal factors in the intensification of mass transfer. There is also evidence that electrically enhanced contacting is beneficial in the presence of impurities such as surface-active agents, non-Newtonian rheology, and in the presence of biopolymers. For example viscous biologically active media can be dispersed electrostatically with relative ease and in a manner which gives rise to an unstable dispersion which is readily coalesced. Earlier studies have accurately predicted charged droplet motion in Newtonian systems as a function of charge, external geometry and physical properties using novel finite element techniques. Here we present a preliminary study of the motion of charged drops comprising viscous Newtonian fluids (solutions of sugar), and viscous non-Newtonian fluids (solutions of carboxy-methyl cellulose). In both cases the continuous phase was n-decanol. The goal of the work was to determine the effect of electrical charge and electrical field upon the drop motion of discrete charged drops. The results showed that increases in drop viscosity, and the presence of non-Newtonian rheology inhibits drop motion in electrically charged liquid-liquid systems. There is potential for enhancing liquid-liquid contacting by imposing an electrical charge on the dispersed phase and there are potential advantages when the dispersed phase is viscous or exhibits non-Newtonian behaviour. The ability to spray drops of viscous liquids is evident and mass transfer can be increased. Enhanced acceleration of charged drops following dispersion was not consistently observed and the motion is influenced by a combination of factors including rheological properties, changes in oscillation behaviour, electrical relaxation, and non-linearities in the local electrical field to which the drops are exposed. Further experimentation is required to quantify the effect of a range of electrical field strengths upon drop motion in non-Newtonian system, including an examination of the effect of the properties of the continuous phase and a detailed comparison with uncharged drops of different sizes and rheological properties.