Thermoacoustic Generator Research Articles

C06 多段階音響スターリングエンジン発電機(パルス管冷凍機,熱音響機器及び関連要素と応用システム(2))

We designed and built a multistage thermoacoustic Stirling engine electric generator prototype, where three regenerators aligned in series, not in parallel, enables the power gain of 5.1 with the temperature ratio of 1.95. In this study, we increased the acoustic power level to 17 W from 20 mW in the previous experiment. Additionally, we studied the thermal efficiency of thermoacoustic energy conversion by controlling specific acoustic impedance, in order to verify the multistage thermoacoustic Stirlung engine as a useful energy conversion device.

1Pb-42 For practical use of thermoacoustic electric generation system : The effect of installation positions of resonance tube on electric generation efficiency(Poster Session)

1Pb-42 For practical use of thermoacoustic electric generation system : The effect of installation positions of resonance tube on electric generation efficiency(Poster Session)

Development of Optical Measurement Techniques for Thermo-Acoustic Diagnostics: Fibre-Optic Microphone, Rayleigh-Scattering, and Acoustic PIV

Thermo-acoustic investigations require reliable measurement techniques in hot environments for pressure, density fluctuations with a high dynamic range and acoustic particle velocity. This paper presents recent developments of optical measurement techniques in combustion diagnostics. A fibre-optic microphone based on the interferometric detection of membrane deflections was designed to measure acoustic pressure oscillations. Due to the heat resistant design, the sensor has an upper temperature limitation of approximately 970 K. Rayleigh-Scattering measurements, using the density dependent intensity of scattered light were performed in an unconfined flame with approximately 1600 K to study amplitude and phase distribution of the flame pulsation. Acoustic particle velocity can be determined applying acoustic PIV (particle image velocimetry) technique. This paper shows a way to measure simultaneously the acoustic particle velocity and the locally resolved mean flow velocity of a turbulent flow. Together these non-invasive techniques are applicable to study thermo-acoustic processes and sound generation in combustion chambers or turbines.

Calibration in acoustic detection of neutrinos

Recent developments in acoustic detection of neutrinos have allowed being more optimistic about the possibility of using the technique in neutrino telescopes, but it still remains a technological challenge and the feasibility of this method has to be proven. Calibration has an important role in both, exploiting the technique at the very limit of the knowledge, and in performing the tests that assure its reliability. In this paper we review the different calibration techniques used (or possibly used) in the field. We can classify the calibration activities in two fields, in the lab and “in situ” in neutrino telescopes, covering a very broad range of topics. Acoustic sensors must be first calibrated in the lab in order to know the sensitivity and the time response of the sensors. Depending on constraints different techniques can or should apply. But lab calibration goes beyond this and involves, for example, the understanding of the thermo-acoustic pulse generation. In neutrino telescope sites, a calibration system with acoustic transmitters should be used to monitor the sensitivity and time response of sensors in site, as well as the response to neutrino-like signals. At the same time, it should provide not only a good tool for training the system for an optimized event reconstruction, but a test to the reconstruction as well. Different acoustic systems have been proposed, we will overview them putting especial attention to the use of acoustic transducers which seems the more versatile technique. Last, the positioning and synchronization of the hydrophones and the knowledge of the physical environment including medium properties are also considered as calibration tasks.

C07 多段熱音響スターリングエンジン発電機(パルス管冷凍機,熱音響機器及び関連要素と応用システム(2))

We designed and built a multistage thermoacoustic Stirling engine electric generator prototype. Use of three regenerators aligned in series, not in parallel, makes it different from ordinary Stirling engines. The prototype thermally amplifies the input acoustic power through the Stirling thermodynamic cycles and converts the amplified acoustic power into electricity. Although the gain of acoustic power was 1.76 with a single regenerator, it reached 5.1 when three regenerators were used. The Stirling engine that we developed can function at a low temperature differential.

B212 多段熱音響スターリングエンジン発電機(OS11 廃熱利用技術)

In this study, we designed and built a multistage thermoacoustic Stirling engine electric generator prototype. The prototype consists of a loud speaker operating as a compression piston, a duct, three regenerators, and a voice coil motor (VCM) operating as a expansion piston. Use of three regenerators is the difference from ordinary Stirling engines. While the gain of acoustic power was 1.76 with a single regenerator, it reached 5.1 when three regenerators were used. Since the Stirling engine that we developed can operate with relatively low temperature difference, it has potential applicability to the recovery of exhaust heat.

Numerical simulation of a thermoacoustic wave amplification

We performed a numerical study of the thermal and physical phenomena occurring in thermoacoustic wave generators. The goal of the simulation is to predict the amplification due to thermoacoustics of a wave initially of small amplitude. Therefore, we focus on the stack and the two heat exchangers, which we call the active cell, which is acoustically compact. The resonator area is split into two parts: the active cell, in which heat transfer takes place, and a resonator, in which the flow is acoustic. The flow in the two‐dimensional active cell can be approximated as a low Mach number viscous, conductive flow, subjected to spatially uniform pressure fluctuations. This model is formally derived using asymptotic expansions in terms of Mach number. The focus here is heat transfer between two successive stack plates. The two‐dimensional time‐dependent problem resulting from this model is solved numerically. Outside the active cell, flow in the resonator is described by a reversible acoustic one‐dimensional model. The coupling between the two zones is obtained by matching the velocity at the interface. The acoustics in the resonance tube can be solved using the d'Alembert solution, relating velocities at the interface to velocity values at an earlier time.

振動流によるエネルギー変換・熱輸送現象と応用技術 熱音響音波発生機の振動流れ―共鳴管出口付近の流れ―

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 changes from oscillatory flow at the tube outlet to pulsating flow far downstream.

C01 熱音響発振器における作動ガス種の影響(パルス管冷凍機,熱音響機器及び関連要素と応用システム(1))

Thermo-acoustic machines are attractive energy-conversion devices that achieve simplicity by eliminating parts such as pistons. Uses of various working gases are being studied in thermo-acoustic devices. It is known that the type of gas gives a big influence on operating characteristics of these machines. This paper is concerned with analyzing the effects of working gases, such as helium and argon in a thermo-acoustic generator by employing a numerical simulation based on a nodal analysis. As a result of the simulation, an operating frequency, pressure ratio, work flow and conversion efficiency were obtained. It seems that these data are useful for designing thermo-acoustic machines.

Analysis of the flow in a thermo-acoustic MHD generator with conducting walls

This paper is devoted to the analysis of a pulsating MHD flow in a rectangular channel, submitted to an applied DC magnetic field and an imposed harmonically oscillating thermo-acoustically generated pressure gradient. The resulting AC current is collected by two electrodes placed on one either side of the channel. The walls of the channel are assumed electrically conducting. The channel is considered sufficiently long to justify the hypothesis of a fully developed flow. The analytical solution proposed is based on a simultaneous resolution of the Navier–Stokes and induction equations. This solution is limited to moderate values of the magnetic Reynolds number.

Oscillatory flow in thermoacoustic sound wave generator

Oscillatory flow in a thermoacoustic sound wave generator is described. The thermoacoustic sound wave generator plays an important role in thermoacoustic equipment. The heat exchange between the working fluid and the stack, the acceleration and deceleration of the working fluid and viscous friction loss both in the stack and in the resonance tube influence the performance of the thermoacoustic sound wave generator. Particularly, oscillatory flow significantly influences the heat exchange mechanism between the working fluid and the stack. Temporal changes in pressure and velocity are sinusoidal inside the resonance tube. Flow forms an oscillatory jet just behind the tube outlet, and becomes intermittent far downstream outside the resonance tube. The open-end corrections of 0.63R, that is, the region where oscillatory flow characteristics are maintained downstream in spite of being outside the tube outlet, are confirmed by velocity measurements and flow visualization. Also, they are almost equal to acoustical theoretical results.

C04 熱音響音波発生機の共鳴管出口付近における流れ : 流れ関数による流量変化の確認(パルス管冷凍機,熱音響機器及び関連要素と応用システム(2))

Flow rate changes around the resonance tube outlet of the thermoacoustic sound wave generator are described. Both flow rates and stream functions based on axial velocity amplitude are employed for confirming the flow rate changes here. The optimum propeller positions for wind power generation with the flow in the thermoacoustic sound wave generator have been observed previously. It is confirmed that they are almost equal to those analyzed by flow rates and stream functions based on axial velocity amplitude.

Performance of a Thermoacoustic Sound Wave Generator driven with Waste Heat of Automobile Gasoline Engine.

A new type of thermoacoustic sound wave generator driven with the waste heat of a 4 cycle automobile gasoline engine is described. The exhaust-pipe connected sound wave generator, in which the hot heat exchanger is set in the exhaust pipe in order to recover the waste heat of exhaust gas, is proposed. A temperature of 780°C of exhaust gas in the exhaust is observed. In a conventional thermoacoustic sound wave generator, sound waves originate at a temperature of the hot heat exchanger, TH, of 200-300°C and become sufficient at 700°C. It is confirmed that the new generator generates sufficient sound waves and its performance is almost equal to that of the electric heater driven generator at a thermal input of 300 W, which corresponds to slightly more than 1% of the heat quantity of exhaust gas provided under the condition that the number of engine revolutions is 2 600 r.p.m. and that the throttle opening is 35%.

Thermoacoustic Method for Detection of Powerful Microwave Pulses

We propose a method for detection of the envelope of a microwave nanosecond pulse, which is based on the effect of generation of sound pulses resulting from absorption of electromagnetic waves. We show that to reproduce exactly the envelope shape of a short microwave pulse, it is necessary that the wave be absorbed in a layer of thickness much less than the product of the sound speed and the pulse duration. In searching for conditions ensuring this, we study the process of thermoacoustic generation in thin metal films deposited on quartz substrates. Measurements performed at a wavelength of 8 mm show that the absorption coefficient is maximum if the aluminum-film thickness is 22–25 A. The maximum absorption coefficient amounts to 49% if the wave is incident from the quartz-substrate side. It is important that in this case, the wave reflection coefficient does not exceed 44%, whereas an aluminum plate reflects almost completely (99.8%) the incident-wave power. The phenomena observed in thin metal films are explained theoretically in terms of the anomalous skin effect. An experimental setup for a study of generation of ultrasonic signals by powerful microwave pulses is described.

2401 熱音響音波発生機内の振動流れ : スタックおよび共鳴管内で流体のなす仕事

Oscillatory flow in the thermoacoustic sound wave generator is described. In oscillatory pipe flow, characteristic Richardson effect occurs in the vicinity of the wall. Its flow plays an important role in thermoacoustic phenomena in which direct energy conversion from heat to work (sound waves), and vice versa, is performed with no moving parts. Also, flow in the resonance tube is influenced by its flow on the stack. Fluid work in stack and the resonance tube are discussed.

209 熱音響音波発生機内の振動流れ : スタック上の流れ

Oscillatory flow in the thermoacoustic sound wave generator is described. Thermoacoustic phenomena are noteworthy, which is direct energy conversion from heat to work (sound wave) with no moving parts. Especially, oscillatory flow on the stack which set in the resonance tube plays an important role in thermoacoustic phenomena. Richardson's annular effect occurs and phase between pressure and velocity shifts in the vicinity of the tube wall. Some analyses of its flow are performed.

D06 熱音響発信器の基本特性解析

Over the past several years, much interest has been devoted to the study of thermoacoustic machines that have the simple construction and do not use the ozone depleting fluid. It is important to understand the thermoacoustics characteristics for developing thermoacoustic machines. This paper is concerned with analyzing the detailed behavior of thermoacoustic machines by using a numerical cycle simulation. Complete differential equations of continuity, momentum and energy of working gas, as well as energy of stack and heat exchanger walls are employed as the governing equations. The experimental results are also discussed to confirm its validity. In this report a typical thermoacoustic generator is adopted.

D12 自動車用エンジンの廃熱を利用する熱音響音波発生機の性能(熱音響エンジン)

A new type of thermoacoustic sound wave generator utilizing the waste heat of a 4-cycle automobile gasoline engine is described. The exhaust-pipe-connected sound wave generator, in which the hot heat exchanger is set in the exhaust pipe in order to recover the waste heat of exhaust gas, is proposed. A temperature of 780℃ of exhaust gas in the exhaust is observed. In a conventional thermoacoustic sound wave generator, sound waves originate at a temperature of the hot heat exchanger, T_H, of 200〜300℃ and become sufficient at 700℃. It is confirmed that the new generator generates sufficient waves and its performance is almost equal to that of the electric-heater-driven generator at a thermal input of 300W, which corresponds to slightly more than 1% of the heat quantity of exhaust gas provided under the condition that the number of engine revolutions is 2600rpm and that the throttle opening ratio is 35%.

Characteristics of Coupled Types of Thermoacoustic Sound Wave Generators.

New types of thermoacoustic sound wave generators, which play an important role in the thermoacoustic refrigerator, are developed. The thermoacoustic sound wave generator consists of hot and cold heat exchangers, stack and resonance tube which is made of stainless steel and Plexiglas tubes, 32 mm in inner diameter and 860 mm long. The theoretical sound wave frequency is 100 Hz. First, two sound wave generators are connected with each other either at the open ends or the closed ends. When they are connected at their open ends, their velocity, pressure amplitude and heat transfer are considerably improved compared with those of independently operated ones. Each phase of both velocity and pressure is inverted automatically. However, when they are connected at their closed ends, their velocity, pressure amplitude and heat transfer are almost equal to those of independently operated ones, and each phase is synchronized automatically. Second, a loop-type sound wave generator constructed of four sound wave generators and four bent tubes is developed. Its sufficient performance is also confirmed.

ループ型熱音響音波発生機の特性

The characteristics of a new loop-type thermoacoustic sound wave generator, in which two closed-end connected-type generators are connected to each other at the open ends by four bent tubes and sealed hermetically, are described. It has been reported that two types of sound wave generators, in which two identically shaped systems are connected to each other at either the open ends or the closed ends, can operate stably. In the new loop-type sound wave generator, which has the benefits of the above-mentioned types of sound wave generators, the pressure, velocity amplitude, acoustic intensity, and heat transferred by sound waves are greater than those of the other connected-type ones. And harmonics in pressure signals and no harmonics in velocity signals are observed at the connected part. An optimum theoretical sound wave frequency of 100Hz is also confirmed for this type of sound wave generator.