title: Influence of acoustic pressure and bubble sizes on the coalescence of two contacting bubbles in an acoustic field.
abstract: In this study, the coalescence time between two contacting sub-resonance size bubbles was measured experimentally under an acoustic pressure ranging from 10kPa to 120kPa, driven at a frequency of 22.4kHz. The coalescence time obtained under sonication was much longer compared to that calculated by the film drainage theory for a free bubble surface without surfactants. It was found that under the influence of an acoustic field, the coalescence time could be probabilistic in nature, exhibiting upper and lower limits of coalescence times which are prolonged when both the maximum surface approach velocity and secondary Bjerknes force increases. The size of the two contacting bubbles is also important. For a given acoustic pressure, bubbles having a larger average size and size difference were observed to exhibit longer coalescence times. This could be caused by the phase difference between the volume oscillations of the two bubbles, which in turn affects the minimum film thickness reached between the bubbles and the film drainage time. These results will have important implications for developing film drainage theory to account for the effect of bubble translational and volumetric oscillations, bubble surface fluctuations and microstreaming.
authors.affiliation: Department of Mechanical Engineering, Nanjing University of Science and Technology, Jiangsu, China; Particulate Fluids Processing Centre, School of Chemistry, University of Melbourne, Parkville, VIC 3010, Australia.
authors.forename: Junjie
authors.initials: J
authors.lastname: Jiao
authors.affiliation: Department of Mechanical Engineering, Nanjing University of Science and Technology, Jiangsu, China. Electronic address: yhe1964@mail.njust.edu.cn.
authors.forename: Yong
authors.initials: Y
authors.lastname: He
authors.affiliation: National Institute of Advanced Industrial Science and Technology (AIST), 2266-98 Anagahora, Shimoshidami, Moriyama-ku, Nagoya 463-8560, Japan.
authors.forename: Kyuichi
authors.initials: K
authors.lastname: Yasui
authors.affiliation: Particulate Fluids Processing Centre, Chemical and Biomolecular Engineering, University of Melbourne, Parkville, VIC 3010, Australia.
authors.forename: Sandra E
authors.initials: SE
authors.lastname: Kentish
authors.affiliation: Particulate Fluids Processing Centre, School of Chemistry, University of Melbourne, Parkville, VIC 3010, Australia.
authors.forename: Muthupandian
authors.initials: M
authors.lastname: Ashokkumar
authors.affiliation: Mechanical and Product Design Engineering, Faculty of Science, Engineering & Technology, Swinburne University of Technology, Hawthorn, VIC 3122, Australia.
authors.forename: Richard
authors.initials: R
authors.lastname: Manasseh
authors.affiliation: Particulate Fluids Processing Centre, Chemical and Biomolecular Engineering, University of Melbourne, Parkville, VIC 3010, Australia. Electronic address: jytlee@unimelb.edu.au.
authors.forename: Judy
authors.initials: J
authors.lastname: Lee
keywords: Acoustic pressure; Bubble size; Coalescence; Film drainage time; Secondary Bjerknes force; Volume oscillations