Performance of a thermoacoustic prime mover without a stack Free

A standing‐wave thermoacoustic prime mover which does not contain a stack has been constructed and tested. The device consists of two heat exchangers and a resonator body. The cold heat exchanger may be moved relative to the hot heat exchanger while the resonator is sealed and thermoacoustically generated sound is present. The device has a cross‐sectional area of about 500 cm² and operates near 600 Hz with ambient air as the working gas. It will be explained how a no‐stack thermoacoustic device may in principle have a greater efficiency than a stack‐based device. In contrast to the well understood stack‐based standing wave thermoacoustic engines, it is expected that the efficiency for a no‐stack device will be nearly proportional to the acoustic pressure amplitude. Preliminary measurements on the device have achieved acoustic pressure amplitudes of 2.5% of the mean pressure. An interesting result is the presence of spontaneous thermoacoustic oscillations even when the gap between the cold and hot heat exchangers is several times larger than the gas displacement, 2x₁. [Work supported by ONR.]