Yusuke Tashiro

Measurements of acoustic streaming in a looped-tube thermoacoustic engine with a jet pump

This paper reports on the acoustic streaming in a looped-tube thermoacoustic prime mover equipped with an asymmetric constriction called a jet pump. The time-averaged mass flow velocity was determined using visualization methods and using acoustic field measurements. It was demonstrated that the magnitude and the direction of the velocity were dependent on the orientation of the jet pump. From the observed velocities, we estimated the heat carried away from the hot heat exchanger by the mass flow. It was shown that the heat loss was decreased from 30 W to 6.5 W by reversing the orientation of the jet pump, when the input heat power supplied to the prime mover was 100 W. The influence of the acoustic streaming was also studied from the cooling temperature of the looped-tube cooler.

Measurements of sound propagation in narrow tubes

The propagation of sound in hollow tubes is a fundamental theme common to many areas of classical acoustics. Kirchhoffs 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. Kirchhoffs theory can be verified by experiment over a wide range of thermodynamical conditions, from isentropic to isothermal.

Acoustic intensity measurement in a narrow duct by a two-sensor method

The use of two pressure sensors [Fusco et al., J. Acoust. Soc. Am. 91, 2229 (1992)] makes it possible to determine the acoustic intensity of a gas column in a duct, but the application of this method was limited to wide ducts. In this letter, the formulation of the method is modified to include narrow ducts where the duct radius is as small as the viscous boundary layer thickness of the gas. The validity of this method is shown by comparison with the direct measurements of the pressure and velocity.

Calibration of a thermocouple for measurement of oscillating temperature

We report on the dynamic calibration of a thermocouple for the measurement of the oscillating temperature. Temperature oscillation is induced in a gas-filled tube by a periodically forced pressure oscillation and measured by a thermocouple. The radial profile of the measured temperature oscillations is compared with the theoretical one, which is determined from the simultaneously measured pressure. A response function of the thermocouple is obtained from the difference in amplitude and phase angle between them by varying the diameter of the thermocouple, oscillating frequency, tube radius, and working gas. We can obtain a true temperature oscillation by using the response function given in this experiment.

Determination of a response function of a thermocouple using a short acoustic pulse

This paper reports on an experimental technique to determine a response function of a thermocouple using a short acoustic pulse wave. A pulse of 10 ms is generated in a tube filled with 1 bar helium gas. The temperature is measured using the thermocouple. The reference temperature is deduced from the measured pressure on the basis of a laminar oscillating flow theory. The response function of the thermocouple is obtained as a function of frequency below 50 Hz through a comparison between the measured and reference temperatures.

Visualization of Acoustic Streaming in a Looped Tube Thermoacoustic Engine with a Jet Pump

The steady flow induced in a looped tube thermoacoustic engine having a jet pump is visualized using a sheet‐like laser light and small tracer particles. It is shown that the acoustic streaming velocity and its direction depend on the configuration of the jet pump. The performance of the looped tube cooler is also shown to be significantly affected by the acoustic streaming induced in the loop.

Amplification of acoustic intensity of a pulse wave propagating through a tube having a temperature gradient

Ceperley has theoretically pointed out that when acoustic traveling waves pass through a long duct with a positive temperature gradient, the acoustic intensity is amplified as a result of the thermodynamic cycles that the gas undergoes. Even though he only observed damping of the acoustic intensity in the experiment, his idea serves as a starting point of new acoustic devices known as thermoacoustic Stirling heat engines. For a further progress of the thermoacoustic technology, experimental verification of his idea is of great importance. In this paper, we report on the thermoacoustic amplification of acoustic intensity using pulse waves traveling in a long tube equipped with a differentially heated regenerator. A reservoir filled with pressurized air and a solenoid valve were used to generate the acoustic pulse running in one direction in the tube with length 60 m. A series of pressure transducers was used to determine the axial distribution of the acoustic intensity. Use of a pulse wave enabled us to se...

Direct observation of thermoacoustic energy conversion

A gas column starts to oscillate when the externally imposed temperature gradient exceeds a critical value. Also, when an acoustic wave propagates through a differentially heated regenerator, the acoustic intensity is thermally amplified. Such thermoacoustic phenomena attract considerable interest not only because it becomes possible to develop pistonless Stirling heat engines, but because an alternative approach to understand a heat engine has been proposed based on energy flows. In this work, we report the direct observation of the thermoacoustic energy conversion in a tube filled with atmospheric air to test the validity of the proposal. A gas column was partly heated by an electrical heater and driven by an oscillating piston at 1.00 Hz to assure good thermal contact with the surrounding tube wall. We simultaneously measured pressure and velocity oscillations to determine the acoustic intensity. As a result, we found the amplification of acoustic intensity in the region with a positive temperature gra...

Response compensation of a thermocouple using a short acoustic pulse

We report on the experimental technique of the measurement of temperature oscillations in acoustic waves. The temperature by a thermocouple is compared with the analytical one derived from a laminar oscillating flow theory. From the differences between them, we derive the response function of the thermocouple. We show continuously the response function in the frequency below 50 Hz using a short acoustic pulse. We can determine the temperature oscillation from the measured one by using the response function.