Acoustic expanders for use in recuperative cryocoolers

An acoustic expander has been developed for use in recuperative cryocoolers. The acoustic expander uses reed-valves to generate a standing acoustic wave from a continuously expanding flow. The mechanical energy from the wave is passively dissipated to the ambient environment. The acoustic expander does not require complex moving parts or control mechanisms at low-temperature; in contrast to piston- or turbo-expanders that require moving displacers or spinning shafts. This expander has demonstrated isentropic expansion efficiencies of 50% for a pressure ratio of 1.4 and expansion efficiencies of 40% for a pressure ratio of 1.9 with air as the working fluid.