Thermoacoustic heat engine

[2] In the 1850s experiments showed that a temperature differential drove the phenomenon, and that acoustic volume and intensity vary with tube length and bulb size.

Further experiments showed that cooling the air at its points of minimal pressure produced a similar amplifying effect.

[2] Orest Symko at University of Utah began a research project in 2005 called Thermal Acoustic Piezo Energy Conversion (TAPEC).

Score Ltd. was awarded £2M in March 2007 to research a cooking stove that also delivers electricity and cooling for use in developing countries.

[8][9] A radioisotope-heated thermoacoustic system was proposed and prototyped for deep space exploration missions by Airbus.

[2] A thermoacoustic device takes advantages of the fact that in a sound wave parcels of gas adiabatically alternatively compress and expand, and pressure and temperature change simultaneously; when pressure reaches a maximum or minimum, so does the temperature.

In a tube closed at both ends, interference can occur between two waves traveling in opposite directions at certain frequencies.

A counter-clockwise Brayton cycle for a refrigerator consists of four processes that affect a parcel of gas between two plates of a stack.

The critical temperature gradient is a value that depends on characteristics of the device such as frequency, cross-sectional area and gas properties.

This may partially offset their lower efficiency, compared to conventional heat engines, as a percentage of Carnot.

However, the narrower pores required to give good thermal contact in a travelling wave device, as compared to a standing wave stack which requires deliberately imperfect thermal contact, also gives rise to greater frictional losses, reducing practical efficiency.