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ECN publication
Lycklama a Nijeholt, J.A.; Tijani, M.E.H.; Spoelstra, S.; Loginov, M.S.; Kuczaj, A.K.
Published by: Publication date:
ECN Biomass & Energy Efficiency 17-7-2012
ECN report number: Document type:
ECN-M--12-030 Conference Paper
Number of pages: Full text:
9 Download PDF  

A thermoacoustic engine converts heat into acoustic energy that can be used to drive the reverse cycle in a thermoacoustic heat pump or a linear generator for the production of electrical power. Relatively high acoustic pressure amplitudes are employed in these sys-tems to obtain sufficient power density and power output. Streaming effects will occur due to these high acoustic pressure amplitudes and due to geometry effects. Streaming is a net steady flow pattern resulting from asymmetric oscillations of the acoustic wave. Streaming leads to undesired convective heat flows, in particular in the thermal buffer zone (TBZ), which strongly limits the efficiency of the engine. Linear acoustic simulation tools cannot be used to predict the effect of streaming. Therefore, Computational Fluid Dynamics (CFD) is utilized to simulate streaming in a torus-shaped thermoacoustic engine. The time-dependent, fully compressible Navier-Stokes equations are iteratively solved in order to simulated the oscillating flow. The CFD model simulates the engine which consists of a to-rus-shaped part with heat exchangers and regenerator. The engine is connected to a resona-tor with an acoustic load. Streaming in the torus-shaped engine has been calculated by means of time-averaging of the simulated oscillating flow. Both a two- and three-dimensional model have been used to predict mass streaming. The modelling approach and streaming re-sults are presented and discussed. The CFD results indicate that streaming in the TBZ is caused by the oscillating flow in the T-junction of the engine. A more streamlined design is recommended as countermeasure to limit streaming in the TBZ.

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