Meier, J. A. and Jewell, J. S. and Brennen, C. E. and Imberger, J. (2011) Bubbles emerging from a submerged granular bed. Journal of Fluid Mechanics, 666 . pp. 189-203. ISSN 0022-1120 http://resolver.caltech.edu/CaltechAUTHORS:20110307-145641113
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This paper explores the phenomena associated with the emergence of gas bubbles from a submerged granular bed. While there are many natural and industrial applications, we focus on the particular circumstances and consequences associated with the emergence of methane bubbles from the beds of lakes and reservoirs since there are significant implications for the dynamics of lakes and reservoirs and for global warming. This paper describes an experimental study of the processes of bubble emergence from a granular bed. Two distinct emergence modes are identified, mode 1 being simply the percolation of small bubbles through the interstices of the bed, while mode 2 involves the cumulative growth of a larger bubble until its buoyancy overcomes the surface tension effects. We demonstrate the conditions dividing the two modes (primarily the grain size) and show that this accords with simple analytical evaluations. These observations are consistent with previous studies of the dynamics of bubbles within porous beds. The two emergence modes also induce quite different particle fluidization levels. The latter are measured and correlated with a diffusion model similar to that originally employed in river sedimentation models by Vanoni and others. Both the particle diffusivity and the particle flux at the surface of the granular bed are measured and compared with a simple analytical model. These mixing processes can be consider applicable not only to the grains themselves, but also to the nutrients and/or contaminants within the bed. In this respect they are shown to be much more powerful than other mixing processes (such as the turbulence in the benthic boundary layer) and could, therefore, play a dominant role in the dynamics of lakes and reservoirs.
|Additional Information:||© 2011 Cambridge University Press. Received 3 December 2009; revised 16 August 2010; accepted 16 August 2010. C.E.B. would like to acknowledge the financial support from CWR for a three month visit in 2009 to the Centre for Water Research, University of Western Australia. This paper also forms publication 2282 JM in the CWR publications series.|
|Subject Keywords:||bubble dynamics; geophysical and geological flows; granular media|
|Usage Policy:||No commercial reproduction, distribution, display or performance rights in this work are provided.|
|Deposited By:||Tony Diaz|
|Deposited On:||08 Mar 2011 18:10|
|Last Modified:||26 Dec 2012 13:00|
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