Experimental improvements to the acoustic expander with applications to cryogenic refrigeration

Abstract The acoustic expander is an innovative cryogenic component that uses pressure waves for work transfer as part of a continuous flow, recuperative cycle refrigerator. This expander uses passive reed-valves coupled to an acoustic resonator to produce refrigeration. The passive reed-valves are pressure-controlled by the imposed, static pressure difference across the expander and the natural oscillating pressure in the resonator. The resonator is a series of tubes and cones. The practical implications of these simple components are that the acoustic expander does not require controlled valving or close-tolerance sliding seals at low-temperature, unlike existing piston- or turbo-expanders. This work compares two resonator designs, a harmonic resonator and a non-harmonic resonator. The non-harmonic resonator is excited by a single-frequency allowing for operation at an expansion pressure-ratio of 2.4. These expanders are expected to be useful in medium-scale refrigeration applications that are not well served by current small-scale Stirling cryocoolers or large-scale turbo-expander refrigerators.