Abstract:

Thermoacoustic engines operating in the standing wave mode are limited in their efficiency by a high degree of irreversibility that is inherent in how they work. Better performance can be achieved by using traveling waves in the thermoacoustic device. This has led to the development of an annular high-frequency thermoacoustic prime mover consisting of a regenerator, which is a random stack in-between heat exchangers, inside an annular waveguide. Miniature devices were developed with operating frequencies in the range of 2--3 kHz. This corresponds to an average ring circumference of 11 cm for the 3-kHz device; the resonator bore is 6 mm. A similar device of 11 mm bore and length of 18 cm was also investigated; its resonant frequency is 2 kHz. Sound power was extracted by an impedance-matching side arm to the annular structure. The spectrum of the acoustic power did not have harmonics, indicative of all traveling wave components. The efficiency is high, being over 40% of Carnot. This type of device shows much promise as a high efficiency energy converter; it can be quite simply reduced in size for microcircuit applications.