Specific acoustic impedance measurements of an air-filled thermoacoustic prime mover

Abstract

Thermoacoustic heat engines can be used to produce sound from heat and to transport heat using sound. The air-filled prime mover studied is a quarter wavelength resonator that produces sound at nominally 115 Hz for a temperature difference of ΔT=176 K. Specific acoustic impedance at the mouth of the prime mover was measured as a function of the temperature difference between the hot and cold heat exchangers. The real part of the impedance changes sign for sufficiently large temperature differences, indicating the possibility of sound production. The theoretically predicted radiation impedance of an open pipe was compared to the measured impedance curves. The operating point was confirmed from the intersection of these experimental and theoretical impedance curves. These measurements allow for analysis of the prime mover as a sound source as discussed in a recent theoretical paper [T. B. Gabrielson, J. Acoust. Soc. Am. 90, 2628–2636 (1991)].