The development of ultrasound techniques for the characterisation of dispersed liquid-liquid flows in small and large channels

This paper presents the development and application of non-intrusive ultrasound techniques for measuring velocity profiles, drop size, and volume fraction distributions in two-phase liquid-liquid flows. These flows are essential in industrial sectors, including energy, chemicals, and pharmaceuticals. Ultrasound waves can penetrate any material, are harmless and less expensive than other techniques such as X-ray, particle image velocimetry (PIV) or NMR, while they can be used in non-transparent test sections. The ultrasound techniques were applied to small (2mm diameter) and large (26mm diameter) test channels. The techniques were based on the measurement of the attenuation coefficient, sound speed, and frequency shift of the propagated sound wave. Signal post-processing methods were developed to obtain drop velocity profiles, drop size distributions, and volume fractions. In the small channel, kerosene was dispersed in glycerol/water flow. In the large test channel, silicone oil was dispersed in either a single-phase water flow or in the water layer of stratified oil-water flows. To validate the ultrasound results, drop size measurements and interface heights were compared against high speed images, while drop velocity profiles were compared against PIV results. The good agreement between techniques shows that ultrasound is a powerful technique for characterizing liquid-liquid dispersions.