Cavitation clusters in lipid systems – surface effects, local heating and streamer formation

Abstract

Cavitation clusters and streamers are characterised in lipid materials (specifically sunflower oil) and compared to water systems. The lipid systems, which are important in food processing, are studied with high-speed camera imaging, laser scattering and pressure measurements. In these oils, clusters formed at an aged (roughened) tip of the sound source (a piston like emitter, PLE) are shown to collapse with varied periodicity in relation to the drive amplitude employed. A distinct streamer (an area of increased flow emanating from the cavitation cluster) is seen in the lipid media which is collimated directly away from the tip of the PLE source whereas in water the cavitation plume is visually less distinct. The velocity of bubbles in the lipid streamer near the cluster on the order of 10 m s -1. Local heating effects, within the streamer, are detected using a dual thermocouple measurement at extended distances. Viscosity, temperature and the outgassing within the oils are suggested to play a key role in the streamer formation in these systems.

Potential Effect of Cavitation on the Physical Properties of Interesterified Soybean Oil Using High‐Intensity Ultrasound: A Long‐Term Storage Study

“…7. These results showed that the number of subharmonics generated during sonication were not affected by the temperature of the samples and that the number of subharmonics is only dependent on the power level employed as previously shown by Birkin et al (2017, 2019). Fig.…”

“…This was recorded by an in-house program (Visual Studio 2010, including Measurement Studio 2012 and USB-204 DAQ card [National Instruments]). A detailed description of the experimental setup can be found in Birkin et al (2017Birkin et al ( , 2019.…”

“…The frequency of subharmonics can be defined as f/N. f indicates the frequency of the HIU and N is an integer value (Birkin et al, 2017(Birkin et al, , 2019.…”

“…7 and 8 show the hydrophone and laser scattering data obtained during HIU application at temperatures of 24 and 34 C, respectively. Previous studies (Birkin et al, 2017(Birkin et al, , 2019 showed that during sonication a cluster of bubbles is formed closed to the tip with a streamer of bubbles that move away from the tip are generated. Cavitation clusters forming and collapsing at various periodicities in oil systems were studied and results showed that these clusters oscillate at a specific frequency and periodicity depending on the levels of HIU amplitude (power level).…”

“…Cavitation itself involves the formation, motion, and collapse of bubbles while exposed to suitable pressure changes (e.g., the ultrasonic waves), resulting in shockwave emission and high localized temperatures (particularly in the gas phase of the collapsing bubbles) (Barcikowski et al, 2019) that can change the physical properties in the resulting media (Abdullah and Chin, 2014;Hosseini et al, 2015;Silva et al, 2017). Cavitation and bubble dynamics have been vastly studied in aqueous systems, but fewer studies have been performed in lipid systems (Birkin et al, 2017(Birkin et al, , 2019. Previous research in our laboratory has reported the presence of bubbles in interesterified soybean oil during high-intensity sonication (Martini et al, 2012).…”