Flow and temperature fields in thermoacoustic stacks

Abstract

The paper describes the flow patterns and the temperature distribution measured in a thermoacoustic engine. Experiments have been performed in a resonant standing wave thermoacoustic refrigerator model. The knowledge of temperature and flow fields in the microchannels and at the edges of the stack plates becomes an increasingly important issue in the design of heat exchangers for thermoacoustic engines. Different geometries of the stack plates have been investigated as well as at different pressure levels. Heat exchangers have also been placed on both sides of the stack, with adjustable gaps. 2-D particle image velocimetry was used to investigate the flow with enlarged observation fields near the ends of the stack plates. We present velocity profiles across the microchannels, 2-D velocity fields. Vorticity maps were deduced using a criterion based on a normalized angular momentum. Vortex motion close to the stack ends has been clearly observed, however, with a strong influence of the plate thickness. An array of miniaturized thermocouples permits us to follow in real time the building-up of the temperature gradient along the stack for different oscillating flow conditions and different gaps between the stack and the heat exchangers. Finally, comparisons are made with theoretical models and numerical simulations recently published in the literature. [Work supported by DGA.]