|Bubbles under acoustic excitation can grow or dissolve due to the mass transfer into/out of the bubbles, termed as rectified (mass) diffusion. As a fundamental phenomenon of acoustic cavitation, rectified diffusion also serves as a paramount effect in many applications, such as bubble sonoluminescence and sonochemistry. For details of this phenomenon, readers are referred to Fyrillas and Szeri (1994, p.381).
Bubble response under acoustic fields with different amplitudes. Adapted from Crum (1980, Fig.4).
Growth of bubble through rectified diffusion. Adapted from Lee (2005, Fig.1).
Recently, the rectified diffusion phenomenon has been investigated during my Ph.D. program with a focus on high-frequency region and near resonance. For example, an improved approach has been proposed for much accurate predictions of rectified diffusion phenomenon near resonance (Zhang and Li, 2011). A dynamic-frequency technique for speeding bubble growth has also been demonstrated and compared with constant-frequency technique (Li and Zhang, 2011). More work has been delivered in my Ph.D. thesis with applications in biomedical engineering.
References
Crum, L. A. (1980). “Measurements of the growth of air bubbles by rectified diffusion,” J. Acoust. Soc. Am., 68, 203-211.
Fyrillas, M. and Szeri, A. J. (1994). "Dissolution or growth of soluble spherical oscillating bubbles," J. Fluid Mech., 277, 381-407.
Lee, J. Kentish, S. and Ashokkumar, M. (2005). “Effect of surfactants on the rate of growth of an air bubble by rectified diffusion,” J. Phys. Chem. B, 109, 14595-14598.
Li, S. C. and Zhang, Y. (2011). “Dynamic-frequency technique for speeding up bubble growth,” Proceedings of WIMRC 3rd International Cavitation Forum, University of Warwick, Coventry, UK, July 4-6, 2011.
Zhang, Y. and Li, S. C. (2011). “Improved theory for near-resonance bubble rectified diffusion with applications,” 2011 IEEE International Ultrasonics Symposium, Orlando, Florida, USA, October 18-21, 2011 (Poster).
Zhang, Y. and Li, S. C. (2011). “Improved theory for near-resonance bubble rectified diffusion with applications,” 2011 IEEE International Ultrasonics Symposium, Orlando, Florida, USA, October 18-21, 2011 (Poster).
Hi Yuning,
ReplyDeleteI have a question for you on rectified diffusion, if it strikes your interest:
Say you have a a cavity with trapped gas, in which the the interface is concave rather than convex like a bubble, i.e., one whereby surface tension points outwards rather than inwards. Would exposure to ultrasound still induce the gas pocket to grow or would it shrink?
It depends. Is there real examples for this?
DeleteCould you please mark out the acoustic frequency applied to the liquid on your plot?
ReplyDeleteHello Yuning,
ReplyDeleteThanks for your post.
Lets consider a bubble inside a droplet of a solution of organic solvent. The solution has a dissolved polymer which acts as a surfactant and is saturated at 1atm with air. Why as the concentration of the polymer increases, the bubble size increases as well?
This is not for a class. I ask because:
1. As diffusion of the droplet takes place, the polymer concentration inside the droplet increases, thus when a bubble (air) nucleates because of solvent diffusion, I think that the prescence of PLA stabilizes it inmediately and thus the bubble can not grow neither can dissolve back. Therefore the average bubble radius in a highly concentrated solution of polymer should not increase. Yet I noticed that the more polymer I add the bigger the bubbles inside the solution.
2. I thought that viscosity also dampens bubble growth
If you can shed some light onto this phenomena Ill greatly appreciate it.
Thank you very much