Impedance tube measurements of thermoviscous functions with a condensable working fluid

Abstract

Theoretical work by Slaton et al. [J. Acoust. Soc. Am. 112, 1414–1422 (2002); 112, 1423–1430 (2002)] develops the linear theory for thermoacoustics when the working fluid has a component which undergoes condensation and evaporation on the stack during the acoustic cycle. In order to test these ideas an impedance tube is used to measure the acoustic impedance in a closed-end driver-pipe system which contains a sample stack. The impedance is measured on the driver side of the stack from pressure measurements of two closely spaced microphones. This may be compared to the impedance computed from a numerical integration from the closed end of the pipe through the stack, using the known or assumed values of the thermoviscous dissipation functions in the stack. Measurements and the theory for a variety of stack materials and working fluids will be presented.