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.

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Operation

This type of heat pump or refrigerator has no ozone-depleting or toxic coolant and has 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 ^[1] 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) ^[2]

Modern research and development of thermoacoustic systems is largely based upon the work of Rott (1980) ^[3] and later Steven Garrett, and Greg Swift (1988) ^[4], 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 a relative Carnot efficiency approaching 40%, which is comparable with low end domestic vapor compression systems today (high end compressors have efficiencies up to 65%) and heat engines are in most cases superior to automotive internal combustion engines. ^[5]

Demonstration and DIY

It is possible to make your own thermoacoustic hot air heat pump. Here is a recipe, that use available and inexpensive materials. ^[6]

Historical

The history of thermoacoustic hot air engines start about 1887, where Lord Rayleigh discusses the possibility of pumping heat with sound. Thereafter there is only small amount of research. In 1969 Rott broke the research silence. ^[7]

A very simple thermoacoustic hot air engine is the Rijke tube invented/discovered by Pieter Rijke, that converts some heat into acoustic energy. ^[8]

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. ^{[9] [10]}

Major 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. ^[11]

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). ^{[12] [13]}

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. CSI has an Exclusive License Agreement with the U.S. Government for this patented technology. The company's patents cover the USA, Canada, Mexico, England (UK?), Italy, Japan and the Netherlands. Thermoacoustics can reduce your air-conditioning and heating bills up to 80% when using electricity from the power grid and save 100% using solar during daylight hours when cooling demands are always the highest. 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. ^[14]

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. ^[15]

References

1. ^ Not in the sense of angular resolution: See Lord Rayleigh (1878). "The explanation of certain acoustical phenomena". Nature (London) 18: 319-321.
2. ^ Ceperley, P. (1979). "A pistonless Stirling engine – the travelling wave heat engine". J. Acoust. Soc. Am. 66: 1508-1513.
3. ^ Rott, N. (1980). "Thermoacoustics". Adv. Appl. Mech. 20 (135).
4. ^ Swift, G.W. (1988). "Thermoacoustic engines". J. Acoust. Soc. Am. 84: 1145-1180.
5. ^ lanl.gov: More Efficient than Other No-Moving-Parts Heat Engines Quote: "...Already the engine's 30% efficiency [Comment: Absolute] 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..."
6. ^ 2001, Tabletop thermoacoustic refrigerator for demonstrations, Daniel A. Russell and Pontus Weibull (pdf) Quote: "...An inexpensive less than $25 tabletop thermoacoustic refrigerator for demonstration purposes was built from a boxed loudspeaker, acrylic tubing and sheet, a roll of 35 mm film, fishing line, an aluminum plug, and two homemade thermocouples..."
7. ^ Thermoacoustic Oscillations, Donald Fahey, Wave Motion & Optics, Spring 2006, Prof. Peter Timbie
8. ^ P. L. Rijke (1859) Philosophical Magazine, 17, 419-422.
9. ^ 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....", images
10. ^ Videos from Youtube: Twin cylinder thermo-acoustic Stirling Engine #2, Lamina Flow Stirling Engine, Mystery Engine, Solar powered thermo-acoustic Stirling Engine
11. ^ 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..."
12. ^ May 27, 2007, Cooking with sound: new stove/generator/refrigerator combo aimed at developing nations
13. ^ SCORE (Stove for Cooking, Refrigeration and Electricity), illustration
14. ^ Cool Sound Industries, Inc.
15. ^ Ben and Jerry's (flash), Ben & Jerry's

• Gardner, D. & Swift, G. (2003). "A cascade thermoacoustic engine". J. Acoust. Soc. Am. 114 (4): 1905–1919.
• Frank Wighard "Double Acting Pulse Tube Electroacoustic System" US Patent 5,813,234
• Pavement "Coolin' By Sound" B-Side of "Range Life" single - 1994