Thermoacoustic hot air engine

Thermoacoustic hot air engines (Sonic heat pump and refrigeration or thermoacoustic heat pump and refrigeration) of which nearly all are thermoacoustic stirling engines is a technology that uses high-amplitude sound waves in a pressurized gas to pump heat from one place to another - or uses a heat temperature difference to induce sound, which can be converted to electricity with high efficiency, with a (piezoelectric) loudspeaker.

Operation

This type of heat pump or refrigerator has no ozone-depleting or toxic coolant and few moving parts. A device consisting of a series of small parallel channels, referred to as a ‘stack’, is fixed in place at a set location inside the tube. In a standing wave thermoacoustic engine, the pressure and velocity fluctuations through the stack are such that heat is given to the oscillating gas at high pressure and removed at low pressure; this satisfies Rayleigh’s criterion [Not in the sense of angular resolution: See cite journal | author=Lord Rayleigh | title=The explanation of certain acoustical phenomena | journal=Nature (London) | year=1878 | volume=18 | pages=319–321] [Rayleigh's thermoacoustic criterion: "If heat be given to the air at the moment of greatest condensation, or be taken from it at the moment of greatest rarefaction, the vibration is encouraged. On the other hand, if heat be given at the moment of greatest rarefaction, or abstracted at the moment of greatest condensation, the vibration is discouraged." John Wm. Strutt, Baron Rayleigh, "The Theory of Sound," 2nd ed. (London: Macmillan, 1896) (reprinted by Dover Publications (N.Y., N.Y.) in 1945), vol. 2, page 226.] for self-sustained oscillation and by this process heat is converted into acoustic power. For thermoacoustic pumps, the process is reversed. By using thermal delays in the stack, this process approximates the highly efficient Stirling Cycle, but without the cranks, sliding seals or excess weight found in Stirling engines. Ceperley (1979) [cite journal | author=Ceperley, P. | title=A pistonless Stirling engine – the travelling wave heat engine | journal=J. Acoust. Soc. Am. | year=1979 | volume=66 | pages=1508–1513 | doi=10.1121/1.383505]

Modern research and development of thermoacoustic systems is largely based upon the work of Rott (1980) [cite journal | author=Rott, N. | title=Thermoacoustics | journal=Adv. Appl. Mech. | year=1980 | volume=20 | issue=135] and later Steven Garrett, and Greg Swift (1988) [cite journal | author=Swift, G.W. | title=Thermoacoustic engines | journal=J. Acoust. Soc. Am. | year=1988 | volume=84 | pages=1145–1180 | doi=10.1121/1.396617] , in which linear thermoacoustic models were developed to form a basic quantitative understanding, while commercial interest has resulted in niche applications such as small to medium scale cryogenic applications. The technology is also suitable for air-conditioning for homes, commercial buildings, vehicles and other cooling and heating applications.

Efficiency

The "most" efficient thermoacoustic devices built to date have an efficiency approaching 40% of the Carnot limit, or about 20% to 30% overall (depending on the heat engine temperatures). The efficiency of high-end TA engine is comparable with an average internal combustion engine, or with low-end domestic vapor compression systems (a high-end compressor by itself will yield efficiencies of up to 65% for the compression process alone, however the overall cycle efficiency will be much less, due to the Carnot limit).

Higher hot-end temperatures may be possible with TA devices because there are no moving parts, thus allowing the Carnot efficiency to be higher. This may partially offset their lower efficiency, compared to conventional heat engines, as a percentage of Carnot, thus yielding overall efficiencies similar to conventional heat engines.

"...the engine's 30% [absolute] efficiency and high reliability may make medium-sized natural-gas liquefaction plants (with a capacity of up to a million gallons per day) and residential cogeneration economically feasible..." [ [http://www.lanl.gov/mst/engine/ lanl.gov: More Efficient than Other No-Moving-Parts Heat Engines] ]

Historical

The history of thermoacoustic hot air engines start about 1887, where Lord Rayleigh discusses the possibility of pumping heat with sound. Little further research occurred until Rott's work in 1969. [ [http://uw.physics.wisc.edu/~timbie/P325/Fahey_thermoacoustic_oscillations.pdf Thermoacoustic Oscillations, Donald Fahey, Wave Motion & Optics, Spring 2006, Prof. Peter Timbie] ]

A very simple thermoacoustic hot air engine is the Rijke tube invented/discovered by Pieter Rijke, that converts some heat into acoustic energy. [P. L. Rijke (1859) Philosophical Magazine, 17, 419-422.]

An older thermoacoustic hot air engine, where the speaker is replaced by a working piston, is the "Lamina Flow engine" or Lamina Flow Beta Stirling engine. [ [http://www.stirlingengines.org.uk/thermo/lamina.html Robert Sier. 2002: A Simple Lamina Flow Engine] Quote: "... In practice the layout is not so simple as a true acoustical heat engine requires a resonate gas circuit... The engine bears some resemblance to the thermoacoustic engine but differs in not using resonate tubes. Also unlike the Tailer "thermal lag" engine its operation requires a regenerator stack....", [http://www.stirlingengines.org.uk/thermo/lamina2.html images] ] [Videos from Youtube: [http://www.youtube.com/watch?v=Dc2QoP0JQSA Twin cylinder thermo-acoustic Stirling Engine #2] , [http://www.youtube.com/watch?v=cjjkj-UGboM Lamina Flow Stirling Engine] , [http://www.youtube.com/watch?v=BdDQCdfGfYY Mystery Engine] , [http://www.youtube.com/watch?v=TWbMTk1rQ0g Solar powered thermo-acoustic Stirling Engine] ]

Event(s)

Orest Symko began a research project in 2005 called "Thermal Acoustic Piezo Energy Conversion" (TAPEC). The research group has built several prototypes, including a ring-shaped model designed by student Ivan Rodriguez that currently has the highest efficiency. [ [http://www.physorg.com/pdf100141616.pdf physorg.com: A sound way to turn heat into electricity (pdf)] Quote: "...Symko says the devices won’t create noise pollution...Symko says the ring-shaped device is twice as efficient as cylindrical devices in converting heat into sound and electricity. That is because the pressure and speed of air in the ring-shaped device are always in sync, unlike in cylinder-shaped devices..."]

The development of a combined electrical generator, refrigerator based on two coupled thermoacoustic Stirling engines, has recently been disclosed. The name is "SCORE" ("Stove for Cooking, Refrigeration and Electricity"). [ [http://arstechnica.com/news.ars/post/20070527-new-stove-generator-refrigerator-combo-aimed-at-developing-nations.html May 27, 2007, Cooking with sound: new stove/generator/refrigerator combo aimed at developing nations] ] [ [http://www.score.uk.com/research/ SCORE (Stove for Cooking, Refrigeration and Electricity)] , [http://www.score.uk.com/research/Scorepics/Forms/DispForm.aspx?ID=11 illustration] ] Score was awarded £2M in March 2007 to research a cooking Stove that will produce electricity and cooling using the Thermo-acoustic effect for use in developing countries. The consortium comprises: The University of Nottingham (lead), The University of Manchester, Queen Mary University of London, Imperial College London, City University London and the Charity Practical Action (all in based the UK) and is supported by Los Alamos Laboratories in the USA. They expect to have a prototype developed at the end of 2008 with large scale production due in 2012.

Cool Sound Industries, Inc. (CSI) is engaged in a high-tech development effort to commercialize a new line of environmentally safe Air-conditioning and Heating equipment that is not dependent upon any ozone-destroying or planet-warming fluids used by most vapor-compression systems today. The company's patents cover the USA, Canada, Mexico, Great Britain, Italy, Japan and the Netherlands. Thermoacoustics can increase air-conditioning and heating efficiencies up to 80% when using electricity from the power grid and up to 100% using solar during daylight hours when cooling demands are always the highestFact|date=May 2008. The technology was developed in conjunction with the Department of Energy, NASA, Los Alamos National Lab and their related Universities. The technology also conforms to the new standards set by the United Nations and the Montreal Protocol for cooling and heating. [ [http://www.coolsound.us Cool Sound Industries, Inc.] ]

Ben and Jerry's ice cream employed the researchers at Penn State to test and develop a working prototype of a thermoacoustic refrigerator to be unveiled at Earth Day 2004. [ [http://www.benjerry.com/assets/flash/our_company/sounds_cool/soundsCool.cfm Ben and Jerry's (flash)] , [http://www.benjerry.com/our_company/sounds_cool/ Ben & Jerry's] ]

References

*
* Frank Wighard "Double Acting Pulse Tube Electroacoustic System" US Patent 5,813,234

See also

*Sound Amplification by Stimulated Emission of Radiation

External links

* [http://www.lanl.gov/thermoacoustics/ Los Alamos National Laboratory, New Mexico, USA]
* [http://www.acs.psu.edu/thermoacoustics/ Penn State University, USA]
* [http://www.americanscientist.org/template/AssetDetail/assetid/21006?fulltext=true&print=yes The Power of Sound] , "American Scientist Online"
* [http://www.mecheng.adelaide.edu.au/anvc/thermoacoustics/ Thermoacoustics at the University of Adelaide, Australia] , [http://www.mecheng.adelaide.edu.au/anvc/thermoacoustics/forum/ Discussion Forum]
* [http://www.qdrive.com/ Clever Fellows Innovation Consortium]
* [http://www.coolsound.us/ Cool Sound Industries, Inc.]
* [http://www.mecheng.adelaide.edu.au/anvc/publications/public_papers/2005/preprint_bamman_aas2005.pdf ]