Experimental determination of thermoacoustic stack properties

• Main Author: Simmons, Timothy G
• Format: Dissertation
• Language: English
• Subjects: physics, acoustics

The stack plays a key role in the operation of thermoacoustic devices. It is the physical structure that imposes boundary conditions on the oscillating gas, which in turn provide the critical phase relationships necessary for beneficial heat, and/or work flows. Therefore, having the ability to characterize appropriate properties of the stack is of the utmost importance in maximizing the contribution of the stack to the over-all performance of a particular thermoacoustic application. Determining these characteristic properties is the ultimate aim of this work. A pressure-sealed impedance tube was designed and constructed. The tube allowed for relative positioning of the stack sample with respect to the acoustic source (loudspeaker) and rigid termination. Using a two-microphone transfer function technique, measurements of specific acoustic impedance were taken for different stack types with and without a temperature gradient imposed across the stack. These measurements were used in an attempt to determine the thermoviscous functions of the stack samples. Error sources in the measurements, differences between measurement and theory, and sensitivities in the inversion process could not be overcome to make calculation of the stack properties produce reliable results. An analysis of the errors involved in the measurement of specific acoustic impedance and the inversion calculation is discussed.