A thermoacoustic-Stirling heat engine: Detailed study

TLDR

Acoustic streaming can degrade the engine’s efficiency. The study introduces a traveling‑wave thermoacoustic engine and analyzes its irreversibilities to identify components needing further research for higher efficiency. The engine uses traveling waves with reversible heat transfer, suppressing acoustic streaming through surface tapering and nonlinear pressure differences. Measurements show the engine outperforms standing‑wave designs by over 50 %, delivering 710 W at 30 % thermal efficiency (41 % of Carnot) and 890 W at 22 % efficiency, with nearly complete elimination of streaming heat loads and well‑understood dynamics, though streaming suppression details remain qualitative.

Abstract

A new type of thermoacoustic engine based on traveling waves and ideally reversible heat transfer is described. Measurements and analysis of its performance are presented. This new engine outperforms previous thermoacoustic engines, which are based on standing waves and intrinsically irreversible heat transfer, by more than 50%. At its most efficient operating point, it delivers 710 W of acoustic power to its resonator with a thermal efficiency of 0.30, corresponding to 41% of the Carnot efficiency. At its most powerful operating point, it delivers 890 W to its resonator with a thermal efficiency of 0.22. The efficiency of this engine can be degraded by two types of acoustic streaming. These are suppressed by appropriate tapering of crucial surfaces in the engine and by using additional nonlinearity to induce an opposing time-averaged pressure difference. Data are presented which show the nearly complete elimination of the streaming convective heat loads. Analysis of these and other irreversibilities show which components of the engine require further research to achieve higher efficiency. Additionally, these data show that the dynamics and acoustic power flows are well understood, but the details of the streaming suppression and associated heat convection are only qualitatively understood.