Experimental visualization and heat transfer analysis of the oscillatory flow in thermoacoustic stacks

The oscillatory flow field induced by an acoustic standing wave is visualized at the end of the parallel-plate thermoacoustic stacks by Particle Image Velocimetry (PIV) measurements. At first, the velocity fields and vorticity maps in two typical stages of the oscillatory flow are displayed. The heat transfer processes in oscillatory flow are analyzed and discussed. Then, the influences of some key factors including the driving power, the plate thickness, the spacing and the plate shape end on the ejection vortices are presented. Finally, the displacement amplitude of suction vortices is revealed in the channel between the plates. The results indicate that the driving power, the plate thickness and the spacing should be well optimized such that more working gas can be ejected from the ends of the stacks and longer moving path of the ejection vortices can be obtained, which benefits the heat transfer between the working fluid and the heat exchanger. Also, it is shown that the displacement amplitude of the suction vortices in the channel can be enhanced with increasing the driving power. In the design of the stacks, the plate length should be longer than the displacement amplitude of the suction vortices such that the direct heat transfer between the two heat exchangers at the ends of the stack can be avoided.

► The oscillatory flow field at the end of the plates is visualized using PIV device.
► The heat transfer processes of the oscillatory flow are analyzed and discussed.
► The influences of some key factors on the ejection vortices are presented.
► Large KC number should be preferred to improve the performance of the engine.
► The plate should be longer than the peak displacement of suction vortices.