Thermoacoustics work both ways. Simply put, heat makes sound, sound makes heat.Thermoacoustics is heat that makes noise and noise that makes heat. More specifically sound oscillations that transport heat or cold, both of which can be used to generate sound oscillations. A definition is in order – it’s the study of phenomena influenced by thermodynamics and acoustics. Most regard a sound wave in gas as simply pressure and motion oscillations, but neglect to include temperature oscillation which is always present, too. The second law of thermodynamics comes into play when heat is transformed into sound waves, or using sound wave oscillations to transport heat. I read the account of a freelance writer trying to understand thermoacoustics as explained by a Los Alamos scientist in scientific terms. The author of the piece admitted he was totally lost. Anyway, I hope I haven’t lost you so far. If you want a strictly scientific explanation, go here. Or enter Thermoacoustics+Los Alamos, or NASA in your search engine. Basically, a student of the thermoacoustics effect will quickly discover the effect is useful as a heat engine. The prime mover of such a device is heat, with which sound is generated. In other words, the effect is the conversion of heat energy to acoustic energy and visa versa. Engines and refrigeration are both active applications of the effect. The main benefit is devices without any moving parts. See Figure 1 right. A tube and an assembly called the stack containing pressurized gas. 
The stack is a bundle of small tubes, better yet, a solid yet porous substance with many channels through which the gas can pass in either direction can also be used. The porous substance is analogous to the minute opening in tissue, like the skin of an animal. The pores serve as an outlet for perspiration, or in a plant leaf or stem, serving as a means of absorption and transpiration. Sound waves generated by (for example) a loud speaker, oscillate in the tubes, forcing the gas to move in and out through the stack at the resonate frequency of the sound, see Figure 2.
Therefore, a portion of gas thermally expands at high pressure and contracts at low pressures. This action amplifies the pressure oscillations of the reverberating sound waves. The process continues by transforming the heat energy into acoustic energy, and so on. Basically, the thermoacoustics principles are based upon the first law of thermodynamics; i.e., the conversion of one form of energy into another such as heat into motion. Moreover, thermodynamics deals with heat and its relation to macroscopic quantities such as volume, temperature and pressure which can be visually observed. In this case, sound oscillations and their conversion. However, sounds come from standing waves of a given wavelength. Its length is about twice that of the tube and is known as the fundamental frequency. The frequency is a product of fractional periods, repeating over regular intervals of time, making up the wavelength. The frequency of the wavelength relates to the resonance of the system.
Similar to sound waves traveling through water, the same applies to air and gas. Sound waves create pressure and motion in the gaseous medium. Along with these motions, temperature also oscillates. Then, should these oscillations travel through gas in small channels, heat flows to and from the passageways walls. When waves in water encounter narrow passages, as in air, the wavelets reverberate between the channel walls, except no heat is exchanged. Sound waves spatial relationship to small passageways transfer heat to and from the walls something like wavelets rebounding between the walls. The difference is the sound oscillations are not allowed to reach equilibrium, however they do convert heat to sound and visa versa, unlike water. Combined, these oscillations produce a smorgasbord of thermoacoustic effects. Pick the effect you wish to harness.
Now, in the familiar everyday world, these thermal effects go unnoticed. For instance, the amplitude of sound oscillation during ordinary conservation is only about 0.0001°C. On the other hand if an exceedingly powerful sound wave is generated in pressurized gas, the thermoacoustic effects can be harnessed to create powerful Stirling engines, pulsating combustion, heat pumps and efficient refrigeration. It appears that acoustic power is a reliable valuable asset in the arsenal of alternative energy sources, a technology that can produce a plethora of mechanical and electrical energy resources. The question is, just how can the power output of such devices be adjusted for practical use? Depending upon the application, the psi of the gas in a device will in large part determine its power output; i.e., a thermoacoustic generator will produce greater power as gas pressures are increased or decreased for a given generator size.
Or, take a look at the primitive heat flute tuba or clarinet depending on the length and diameter of the tube. The screen could be replaced with a wad of steel wool. Use a candle as the heat source - then listen up! See drawing right.As you look into this science, you will discover pulse tube refrigeration; a close cousin to thermoacoustic refrigeration. Pulse tube cooling was developed to provide extremely low - cryogenic temperatures.
Refrigeration generally uses old applied sciences. Thermoacoustics provides a fresh approach in the heating ventilation and air conditioning (HVAC) fields. This state of the art technology offers environmentally safe operation, low noise, low vibration, and low maintenance, no chemicals. Consumer potable water coolers, liquefaction of industrial gases, cooling sensitive electronics devices, energy star home cooling and freezing appliances. Even space telescopes such as Hubble Spitzer and XMM Newton; not to forget Ben and Jerry’s ice cream freezers. For more possibilities, see the list below. This technology - goes n goes, in fact the possibilities are virtually endless. The links below list just a few:
Links: Thermoacoustics is an exciting technology, check out what else is available.  Custom Search
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Then, if the temperature difference across the stack is large enough, the sound oscillations will compress and heat a portion of the gas which remains cooler than the stack resulting in absorption of some of its heat. Then when the oscillation shifts the gas to the other end expanding, it cools yet remains hotter than the stack releasing its heat.
