An experimental investigation into the motion of a single drop in a pulsed DC electric field

It has been shown that the separation of high volume fraction water-in-oil dispersions is improved by the application of a pulsed DC electric field. It is thought that the improvement in the rate of separation could be due to the formation of dipoles in the aqueous drops, caused by the action of the electric field, but it is also possible that the drops acquire a charge from the continuous phase. At present there is a lack of fundamental experimental results to support these theories. By studying the motion of a single drop in a uniform pulsed DC field, it is possible to make some deductions about the charging mechanism of the drop. A de-ionized water drop, with a diameter of 100 mu to 400 mu, was positioned in n-dodecane between a pair of parallel plate electrodes, the positive electrode being insulated. The drop motion was recorded using a high-speed video camera. Image analysis enabled the x, y co-ordinates of the drop centre in a sequence of images to be obtained and hence the drop trajectory. The pulsed DC voltage applied across the electrodes was also recorded and could be superimposed onto the drop trajectory to enable any correlation between drop motion and the field applied to be observed. The relationship between the drop motion and the continuous phase conductivity was studied and it was found that as the conductivity was increased, the amplitude of the drop motion decreased. This decrease in drop motion was due to a reduction of the field strength in the n-dodecane as its conductivity was increased, relative to that of the insulation coating. Experiments without the insulation coating are shown to confirm this explanation.