CFD-simulation of oscillatory flow around the heat exchangers of thermoacoustic devices

Thermoacoustic systems rely on conversion between thermal and acoustic (i.e. mechanical) forms of energy. The technology lends itself to various applications such as waste heat recovery to produce useful electricity or cooling power or gas liquefaction and regasification in oil and gas industry. Detailed understanding of the fluid flow processes within the internal structures of thermoacoustic systems, especially the heat exchangers, is seen as one of the ways by which the performance of next generation of thermoacoustic systems can be improved. The current study uses 2-D computational fluid dynamics (CFD) model to perform numerical investigations of thermoacoustic heat exchangers placed in an oscillatory flow induced by a standing wave. The computational domain is chosen from a thermoacoustic rig that is built for characterisation of heat exchangers for thermoacoustic applications. Validation of the present numerical approach is first established. Then the numerical analysis is extended by modifying the geometrical and operating parameters. The geometrical parameter considered is the curvature radius of the aerodynamic shapes attached to the entrance and exit of gas channels of the heat exchangers, mainly to modify the flow characteristics. Cases are run for the drive ratios (i.e. the ratio of maximum pressure amplitude to the mean pressure) ranging from 0.3-3.0%. Turbulent model as suitable for thermoacoustic analysis is selected from the literature. Results are discussed based on velocity profiles and the pressure difference obtained as functions of phase angles in the acoustic flow cycle.