Wednesday, March 02, 2005
Toil and trouble
This week’s issue of Nature features some fascinating insights into the nature of bubble cavitation. Cavitation, for those of you like myself who are weakly versed in the world of physics, is the production of short-lived gas bubbles within a liquid as the result of pressure variation. At extreme velocities, the pressure of a liquid in flow can drop below the vapor pressure of the surrounding liquid, resulting in the formation and expansion of a gas “cavity.” The bubbles formed through this process collapse immediately, compressingly so quickly that energy focusing and a massive increase in temperature occur. The amount of heat in these bubbles has long been suspected as “enormous”, as water vapor bubbles will glow when collapsing. (The term “sonoluminescence” was coined to describe the light production that occurs when cavitation is induced by sound waves, as has been the case for most experimental work on the phenomenon.) Just how hot a single bubble can get has remained elusive, however (prior estimates of temperature have been based on multiple bubbles, where lots of energy is lost due to bubble interactions.) That is, until this week’s paper by David Flannigan and Kenneth Suslick of UIUC. Using noble gas bubbles in sulphuric acid, these authors found internal temperatures as high as 15,000 K. This is no everyday temperature, mind you, even for a physicist. We’re talking “surface of the sun” level heat here. Adding to the remarkable nature of this work, Flannigan and Suslick found that the collapsing bubbles have a plasma core. The fabled state of ionized matter, produced simply by a collapsing bubble.
Perhaps even more amazing, it has been known for some time that cavitating bubbles are produced naturally by the snapping shrimp Alpheus heterochaelis (I would direct the reader to the work of Detlef Lohse and colleagues on this topic). Per its common name, this tiny crustacean snaps its massive “snapper claws” together with such velocity as to propel its lifeless body all the way to Phoenix! And by that, of course, I mean to induce cavitation in the surrounding water. The associated flash of light has been dubbed (wait for it) “shrimpoluminescence”. Now, because this involves multiple bubbles in water rather than a single noble gas bubble, the temperatures are somewhat lower (~5000 K, still incredible, especially considering it’s being made by somebody’s appetizer). I’m not sure if the shrimp bubbles contain plasma, but I would tend to think not, considering that no previous sonoluminescence work (much of which used water) has demonstrated its presence. A pity, that—I would love to imagine that across the oceans, savage little shrimp are incapacitating their prey with honest-to-goodness plasma bursts.
This week’s issue of Nature features some fascinating insights into the nature of bubble cavitation. Cavitation, for those of you like myself who are weakly versed in the world of physics, is the production of short-lived gas bubbles within a liquid as the result of pressure variation. At extreme velocities, the pressure of a liquid in flow can drop below the vapor pressure of the surrounding liquid, resulting in the formation and expansion of a gas “cavity.” The bubbles formed through this process collapse immediately, compressingly so quickly that energy focusing and a massive increase in temperature occur. The amount of heat in these bubbles has long been suspected as “enormous”, as water vapor bubbles will glow when collapsing. (The term “sonoluminescence” was coined to describe the light production that occurs when cavitation is induced by sound waves, as has been the case for most experimental work on the phenomenon.) Just how hot a single bubble can get has remained elusive, however (prior estimates of temperature have been based on multiple bubbles, where lots of energy is lost due to bubble interactions.) That is, until this week’s paper by David Flannigan and Kenneth Suslick of UIUC. Using noble gas bubbles in sulphuric acid, these authors found internal temperatures as high as 15,000 K. This is no everyday temperature, mind you, even for a physicist. We’re talking “surface of the sun” level heat here. Adding to the remarkable nature of this work, Flannigan and Suslick found that the collapsing bubbles have a plasma core. The fabled state of ionized matter, produced simply by a collapsing bubble.
Perhaps even more amazing, it has been known for some time that cavitating bubbles are produced naturally by the snapping shrimp Alpheus heterochaelis (I would direct the reader to the work of Detlef Lohse and colleagues on this topic). Per its common name, this tiny crustacean snaps its massive “snapper claws” together with such velocity as to propel its lifeless body all the way to Phoenix! And by that, of course, I mean to induce cavitation in the surrounding water. The associated flash of light has been dubbed (wait for it) “shrimpoluminescence”. Now, because this involves multiple bubbles in water rather than a single noble gas bubble, the temperatures are somewhat lower (~5000 K, still incredible, especially considering it’s being made by somebody’s appetizer). I’m not sure if the shrimp bubbles contain plasma, but I would tend to think not, considering that no previous sonoluminescence work (much of which used water) has demonstrated its presence. A pity, that—I would love to imagine that across the oceans, savage little shrimp are incapacitating their prey with honest-to-goodness plasma bursts.
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