The power of sound: Thermoacoustic mixture separation process moves from science to application
LOS ALAMOS, N.M., September 2002 -- Acoustic scientists are somewhat astonished that until recently no one had ever discovered that if you put a mixture of two gases in a tube and send a sound wave – a pure tone, not a cacophony – through the mixture, it partially separates with one end of the tube being enriched with one kind of gas and the opposite end enriched with the other.
The discovery came at Los Alamos by accident and now research into the physics of this phenomenon is turning the discovery into more than just simply a scientific curiosity.
Called thermoacoustic mixture separation, the phenomenon is turning out to have a number of potential practical applications, the depth and breadth of which are only now beginning to be explored.
Nature has always been doing thermoacoustic mixture separation in a simple form. For ordinary sound in air, however, the effect is too weak and the re-mixing processes (e.g., the little breezes wafting around your office) too strong that you have never noticed anything as extreme as the oxygen moving to one end of your office and the nitrogen to the other end. It was only due to a design geometry and sound intensity that enhanced the separation process, and suppressed re-mixing, that allowed Los Alamos researcher Philip Spoor to detect the small anomaly in an acoustics experiment that lead to the discovery of the phenomenon.
Practical applications
One of the places where this phenomenon may have the most practical application is in mixture separation in industry. Mixture separation is an enormous business that includes such areas as petroleum refining (i.e., separating crude oil into its various components) and air separation to produce oxygen, nitrogen and argon.
Although the thermoacoustic mixture separation is relatively inefficient compared with the current distillation methods widely used in industries, it might find a critical use in either niche applications, where the simplicity and reliability of the separation process might be more important than energy efficiency, or in difficult separations – such as the separation of isotopes and isomers – where separations are notoriously inefficient even with the best existing technology.
One area where Los Alamos researchers are considering applying thermoacoustic separation is in the separation of hydrogen isotopes. Here, reliability, tritium inventory and cleanliness are the most important issues. Another area under consideration is the enrichment of uranium isotopes where the energy efficiency of thermoacoustic separation seems equal to that of gaseous diffusion. Thermoacoustics might also enable small-scale purification of krypton and xenon radioisotopes at locations close where they are produced and used. Finally, it also may be possible in the future to develop small-scale thermoacoustic separation devices for producing stable isotopes for biological and medical use.
To further investigate the thermoacoustic mixture separation process and determine whether any unexpected difficulties might arise in a practical separation system, Los Alamos researchers have built a thermoacoustic separator to test the process on neon isotopes.
Research support
The Department of Energy's Office of Science, through the Division of Materials Science in the Office of Basic Energy Sciences, has supported this research, as well as much of the research leading to the discovery of thermoacoustic mixture separation.
Los Alamos National Laboratory is operated by the University of California for the National Nuclear Security Administration (NNSA) of the U.S. Department of Energy and works in partnership with NNSA's Sandia and Lawrence Livermore national laboratories to support NNSA in its mission.
Los Alamos enhances global security by ensuring the safety and reliability of the U.S. nuclear stockpile, developing technologies to reduce threats from weapons of mass destruction, and solving problems related to energy, environment, infrastructure, health and national security concerns.
For more Los Alamos news, visit www.lanl.gov.
By Todd Hanson