Investigations of flow morphology around thermoacoustic parallel-plate stacks and heat exchangers

In thermoacoustic engines and refrigerators a compressible fluid undergoes an oscillatory motion in the vicinity of a solid body to facilitate energy transfer between heat and acoustic waves. The solid is often a stack of parallel plates sandwiched between two heat exchangers. The oscillatory flow leads to vortex shedding and vortex impingement at the end of stack and on the stack/heat exchanger interface, which impacts the performance of thermoacoustic devices due to possible modification of heat transfer processes. In this work, the flow phenomena and flow morphology are investigated using PIV. Two case studies are addressed: (i) flow around a single stack of plates, with the objective of relating the plate thickness, plate spacing and the flow displacement amplitude to the distinct vortex shedding flow patterns and defining the relevant non-dimensional parameters governing the shedding; (ii) flow around a system of two stacks "in series" (to mimic stack/heat exchanger arrangement). The latter allows studying the vortex generation and shedding around the plate ends of one stack with the other stack's plates positioned in the wake, the entrance effects into the channels affected by shedding, which will hopefully aid the understanding of how the relevant non-dimensional parameters need to change in realistic thermoacoustic systems.