Performance studies of travelling-wave thermoacoustic engine for selected low-cost regenerators

Operation of thermoacoustic devices is based on the energy transfer between an acoustic wave and a solid material, facilitated by periodic oscillations of a compressible fluid. In travelling wave devices the main component enabling these processes is a "thermoacoustic core", comprising of a regenerator material, sandwiched between two heat exchangers. In thermoacoustic engines the temperature gradient imposed by the heat exchangers leads to spontaneous generation of sound waves. Current engineering practice of fabricating the regenerators uses fine woven wire mesh screens, stacked together layer by layer. This tends to be labour intensive, costly and leads to high viscous losses compared to theoretically best configurations of parallel plates or "pin arrays". In this work we are looking for cheap and easily applied alternatives to stacked wire mesh screens, of at least comparable performance. To this end we constructed a travelling wave engine which is used as a test bed for comparing various candidate materials including: steel wool, metal swarf, metal foam, ceramic or glass spheres and other random geometries. Under the conditions of similar hydraulic radii we test the acoustic power produced, thermal efficiency and onset temperature achieved by selected regenerator configurations for relative comparisons. Detailed discussion of findings is provided.