Whenever something does not have moving parts, engineers get excited. Absence of moving parts means less parts that require lubrication, or can break down, and therefore the system has less maintenance.
Heat engines such as the internal combustion engine, compression refrigeration cycles or steam turbine cycles are widely used, but have great mechanical complexity and require many parts. Is it possible to make heat engines without turbines, pumps, pistons or hydraulic seals?
Yes, one such technology are the so called thermoacoustic engines. They use a compressible gas that vibrates inside a cavity at a resonance frequency. Invented long ago, the first models had poor efficiency, but recent advances achieved increases in efficiency that make them more attractive.
They can operate in direct mode, producing work from a temperature difference, or in reverse mode, as coolers that transfer heat from a cold reservoir to a hot one at the expense of work.
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