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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.
Additional recommended knowledge
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  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) 
Modern research and development of thermoacoustic systems is largely based upon the work of Rott (1980)  and later Steven Garrett, and Greg Swift (1988) , 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.
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. 
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. 
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. 
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. 
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).  
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. 
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. 
|This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Thermoacoustic_hot_air_engine". A list of authors is available in Wikipedia.|