About 30 years ago, Ceperley proposed “a pistonless Stirling engine”, which became sufficient motivation for thermoacousticians to regard thermoacoustic phenomena as a kind of heat engine. Since then work flux, heat flux, and their mutual conversion have been suggested to be fundamental ideas for understanding thermoacoustic engines. Such new concepts can be equally applicable to some reciprocating heat engines. In this paper, based on experimental results, I discuss the working mechanism of Stirling engines from the standpoint of a thermoacoustics framework.
The fundamentals of thermoacoustics constitute understanding thermoacoustic phenomena, the proposal of new thermoacoustic devices, and the development of new experimental techniques. This paper describes a practical guide to measurements of important physical quantities in thermoacoustic systems to help beginners understand the basic techniques. The direct method, involving measurements of pressure and velocity oscillations, and the two-sensor method are introduced for the measurement of work flow. A method for the dynamic calibration of a thermocouple is also presented to make measurements of temperature fluctuation possible. Particular emphasis is given accurately determining the phasing between oscillatory quantities.
This research describes the oscillatory flows inside and outside a thermoacoustic sound-wave generator. Two types of thermoacoustic sound-wave generators are employed. One is a conventional thermoacoustic sound-wave generator, 32 mm in inner diameter and either 860 mm or 1,133 mm long including the high- and low-temperature heat exchangers inside the resonance tube. The other is a simplified thermoacoustic sound-wave generator, 72 mm in inner diameter and 860 mm long, and has no heat exchangers inside the resonance tube. Simultaneous measurements of velocity and pressure were performed inside the resonance tube. Typical oscillatory flows, which include the Richardson effect near the tube wall, were observed inside the resonance tube of both types of sound-wave generator except immediately before the tube outlet. The differences between the inflow and outflow were ascertained near the tube outlet as well. Flow rates based on velocity amplitude are newly proposed for evaluating the flow singularities outside the resonance tube outlet. The forward flow rates, which increase up to 30 mm downstream from the tube outlet, decreased more than 30 mm downstream. On the other hand, the backward flow rates vanished more than 15 mm downstream. We also confirmed that the flow outside the resonance tube outlet