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Thermo Acoustic Refrigeration (TAR)
The idea that sound waves could be used for refrigeration or engines came from the Stirling cycle. The Stirling cycle was based on two cylinders that oscillated 90 degrees out of phase with each other. It was noticed that sound waves actually had this same property, and the concept of the thermoacoustic refrigerator was born.
Generally 130 to 135 Hz under 10 to 30 bar pressure is used in normal TARs.
Since the discovery by Merkli and Thomann that cooling can be produced by the thermoacoustic effect in a resonance tube, research has concentrated on developing the effect for practical applications. One approach in the art has been to increase the audio pumping rate. While the experiments of Merkli and Thomann used frequencies of around 100 Hz, Wheatley et al. successfully raised the operating frequency to around 500 Hz and achieved impressive cooling rates in their refrigerator.
Utilizing a driver that operates at a high frequency allows the device to be made smaller in size as the wavelength at such a frequency is short.
- Review PDF
- Ceramic Substrate Stacks in TARs
- High Frequency (4KHz to Ultrasonics) TAR Patent: A thermoacoustic refrigerator having a relatively small size which utilizes one or more piezoelectric drivers to generate high frequency sound within a resonator at a frequency of between about 4000 Hz and ultrasonic frequencies. The interaction of the high frequency sound with one or more stacks create a temperature gradient across the stack which is conducted through a pair of heat exchangers located on opposite sides of each stack.