T. Yazaki

A heat engine called a pulse tube engine has been recently proposed, which consists of only a few parts, namely, differentially heated stacked metal meshes in a cylinder and one piston, coupled to a flywheel. We built the prototype engine and tested its working mechanism from the standpoint of a thermoacoustic framework. We measured the work flux density distribution over the cross section of the pulse tube to elucidate the work source of the engine. This engine belongs to the standing wave engine group and the work source resides not in the stacked metal meshes but in the pulse tube.

The propagation of sound in hollow tubes is a fundamental theme common to many areas of classical acoustics. Kirchhoff's theory explaining the propagation of sound in a circular tube is now playing an important role as a starting point in studying sound in porous media. This paper reports on measurements of the phase velocity and attenuation coefficient in the narrow regions of tubes, where the sound undergoes anomalous dispersion and is seen to slow down remarkably to the extent that a runner can pass ahead of it. Kirchhoff's theory can be verified by experiment over a wide range of thermodynamical conditions, from isentropic to isothermal.

We have built a thermoacoustic engine consisting of a differentially heated stack of plates in a looped tube and observed spontaneous gas oscillations of the traveling wave mode running around the loop. Stability boundary and thermally produced acoustic power are compared with those for the engine tested in a resonator. The engine in a looped tube acts as a traveling wave power amplifier, whose onset temperature ratios are significantly smaller than those for the engine in a resonator.