Criteria for the selection of porous cores for thermoacoustic applications

The criteria indicated in this paper stem from the analysis of the viscous- thermal behaviour of the three most common typologies of porous cores for standing-wave thermoacoustic engines, namely cores provided with circular pores, with rectangular slits and with array of parallel cylindrical pins. Analytic solutions of spatially averaged thermal and viscous functions are used to describe the sound propagation within the cores by means of the Rott's theory of thermoacoustics. The performances of these three typologies of cores have been computed and compared by modelling the behaviour of a standing-wave thermoacoustic engine operating with different fluids. In previous works the comparison among different cores has been based on the ratio between the acoustic power generated and the power dissipated by viscous losses. Aim of this work is to report the same comparisons but in terms of acoustic power and global efficiency. In this way it is possible to consider all the losses involved in the heat to acoustic power conversion occurring in the core, including the entropy flux and the heat conduction through the stack.