Experimental validation of a looped-tube thermoacoustic engine with a stub for tuning acoustic conditions

Abstract

Thermoacoustic engines with a looped-tube structure and multiple thermoacoustic stages are able to efficiently utilize low-grade heat. If additional measures to counteract acoustic reflections are taken, similar results can be achieved by using only one single stage. The implementation of a stub, which is a compliant duct closed on one side and T-branched to the engine’s loop on the other side, allows a precise tuning of acoustic conditions. By only changing position and length of the stub, phase difference and normalized impedance in the regenerator can be adjusted over a wide range. The method is experimentally validated by this paper. A test-rig is introduced that works with argon at atmospheric pressure. Measurements of thermal and acoustic conditions were conducted for several configurations of the stub. Afterwards, results are used to adjust a numerical DeltaEC-model. The proposed procedure employs simple and reasonable correction parameters. They take minor acoustic losses, non-linear effects and geometrical errors into account. Eventually, the simulated acoustic field is in very good agreement with experimental results. The stub’s acoustic tuning capability is verified. Further, the results show a large mismatch of thermal quantities. Gedeon streaming is expected to be responsible. It is later eliminated by use of a jet pump with a novel design. Hence, a major discrepancy is still observable being related to other effects of thermoacoustic streaming. Eventually, impacts of the jet pump to the acoustic field on system level are analyzed.