Cavitation clusters in lipid systems - Ring-up, bubble population, and bifurcated streamer lifetime.

The processing of oils is vital to their ultimate use within the food industry. Control over the physical properties of such materials could be achieved through the application of high-intensity ultrasound (HIU). However, the exact mechanism, centred upon acoustic cavitation, is currently unclear. To investigate the cavitation environment in oils further, the ring-up of a HIU source in an oil media is studied in the presence and absence of a pre-existing bubble population. High-speed imaging and acoustic measurements within the system is demonstrated to be extremely useful in characterising the dynamics present under non steady-state conditions. The behaviour of the clusters generated in the first 1000 ms under these conditions is shown to be significantly different depending on the bubble population. A bifurcated streamer (BiS), originating from a unique bi-cluster event, is only observable in the presence of a bubble population during the ring-up process to higher cluster orders. In addition, the lifetime of this BiS event is highly temperature dependent and is shown to be a good marker for the viscosity of the oil employed.