Numerical analysis of competing methods for acoustic field adjustment in a looped-tube thermoacoustic engine with a single stage

Abstract

Looped-tube thermoacoustic engines have shown to be operational with low temperatures. When equipped with multiple stages, preferable acoustic conditions are inherently achieved, leading to high efficiency. However, engines with only a single stage are able to achieve a similar performance, when acoustic disturbances are properly matched by implementation of an additional, acoustically effective element. Furthermore, acoustic conditions in the regenerator can be accurately tuned by adjusting the element’s volume (i. e. impedance) and position in respect to the regenerator. The present work compares three different methods for acoustic field adjustment: a side-branched stub, a compliant segment and an inertial segment. The last two are widened or narrowed sections of the feedback loop, respectively. The influence of different general positions is considered. All configurations are analysed and compared with each other regarding their acoustic tuning capabilities and possible side effects to the acoustic field. As a result, superior engine performance is achieved by use of a compliant segment, closely followed by use of a stub. Furthermore, the length of a compliant or inertial segment has a major impact on performance. While extending a compliant segment slightly improves power, it can be crucial for an inertial segment. The comprehensive analysis is carried out numerically under identical conditions for each configuration. DeltaEC (Design Environment for Low-amplitude Thermoacoustic Energy Conversion) is used as simulation software.