Experiments on ultrasonic separation of a model water-in-oil emulsion

Abstract

The dynamics of model water-in-oil emulsions based on PMS-5 and PMS-100 silicone oils in the field of a standing ultrasonic wave is studied experimentally. In the experiments, a resonator cell with transparent walls is used. The ultrasonic transducer is installed in the cell’s vertical wall; its radiation axis is directed horizontally, across the working layer. Experiments are performed at an ultrasonic exposure frequency of ~ 80 kHz and a dispersed phase concentration of 5%. Photo-video recording of the images of the liquid layer in transmitted light is carried out, with their subsequent digital processing. The brightness levels of the patterns of the working fluid layer in the transmitted scattered light are measured. An ultrasonic wave leads to a redistribution of the liquids, which can be distinguished by a change in the brightness patterns of the light passing through the working layer. This is evidence of ultrasonic separation due to acoustophoresis. Two main effects caused by ultrasonic action and preventing the separation of the emulsions are experimentally demonstrated. Ultrasonic oscillations cause cavitation in the liquid volume and also acoustic streaming (primarily the ‘quartz wind’), which become noticeable at a relatively high intensity of ultrasonic exposure. Experiments show that the integral brightness of images varies non-monotonically with change in the intensity of ultrasonic exposure. The nature of this dependence correlates with the manifestation of acoustic streaming and is consistent with the results of other authors.