(77b) Experimental and Simulated Trajectories of Electrically Charged Drops in Non-Newtonian Liquid – Liquid Systems

Process
Intensification of solvent extraction processes for biological products,
production of biodiesel from raw feedstocks, and of phase separations is an
area for the potential small-scale applications of DC electric fields to
liquid-liquid contacting. Simulated design of possible configurations of electrically
enhanced reactors would be important in this context. The aim of this work was
to validate a novel finite element algorithm for the prediction of three-dimensional
trajectories for electrically charged drops. Earlier work had shown
accurate prediction for newtonian liquid-liquid system and for a range of
different contactor geometries. The current work sought to extend this to
non-newtonian liquids. The results of trajectory studies of electrically
charged non-Newtonian liquid drops dispersed into a non-Newtonian, immiscible
continuous phase in an electrically enhanced rectangular glass column are
presented here. Only the electrohydrodynamics of the droplets are studied and
other modes of transport process are not considered. In this study, the
continuous phase was selected on the basis of low electrical conductivity
values (< 10^-10 S/m), a non-Newtonian rheology and optical
transparency. The liquids used as the continuous phase were mixtures of polyisobutylene
in mineral oil. Dispersed phases having a range of rheological properties were
also studied. These included newtonian aqueous solutions, non-newtonian aqueous
solutions of carboxymethyl cellulose (CMC) and aqueous Blanose. The motion of
the droplets in three-dimensional space was videoed using a Sony digital
camera. Image analysis software Image J was used to digitize the videos and to
determine the time dependent xyz trajectory, the velocity data for the droplets
and the corresponding drop sizes. The discrete drop and electrostatic
dispersion regimes were studied. Physical parameters included, interfacial
tension, viscosity, the density of both phases, and electrical conductivity of
the dispersed phases. These were measured to physically explain the droplet
behavior and also to model the system accurately. The effects of the applied D
C electric field, the polarity of the electric field, the nozzle dimensions,
the dispersed phase flow rate, the nozzle insertion depth, and inter electrode
distance upon the trajectories will be presented. Some interesting phenomena
associated with falling drops were observed. These included droplet breakup,
coalescence, and oscillations occurring at higher DC electric fields. These
effects were simulated with the finite element modeling. An initial good match
between the experimental and simulated data was observed.

Keywords: electrically charged drops, D C electric field,
non-newtonian, three dimensional trajectory, finite element analysis