Traveling-wave Thermoacoustic Heat Engine Research Articles

Experimental study of quasi-periodic on-off phenomena in a small-scale traveling wave thermoacoustic heat engine

Periodic and spontaneous on-off oscillation belongs to the onset and damping behaviors of thermoacoustic engines, and investigations on this phenomenon lead to better operation of the thermoacoustic engines with stable performances. In this paper, the quasi- periodic on-off oscillation in a small-scale traveling wave thermoacoustic heat engine with a resonator length of only 1m was experimentally investigated. The type of working media, mean pressure and the input heating power are the main operating parameters, which significantly affect the formation of the periodic on-off oscillation. The experimental results demonstrated there was a critical charge pressure over which the periodic on-off oscillation could happen. For the small- scale engine with helium gas as the working media, the mean pressure threshold value was about 1.4MPa and the on-off oscillation occurred with a single frequency. Using nitrogen and argon gas as the working media, the on-off oscillation was not observed. The reason was qualitatively analyzed as well.

A Novel Multi-stage Looped Thermoacoustic Heat Engine Using Assembly of Elastic Membrane and a Solid Mass

Abstract A compact looped traveling-wave thermoacoustic heat engine (LTTHE) using an assembly of an elastic membrane (EM) and a solid-mass plate (SP) acting as a resonance unit is proposed in this paper. In the novel configuration, the novel resonance assembly substitutes for the traditional resonance tube to reduce the axial size of the system effectively, leading to a compact-size system. In addition, multiple identical engine units are included in a closed loop to realize efficient thermoacoustic conversion and efficient acoustical transmission. In this paper, a typical three-stage thermoacoustic heat engine operating around 300 Hz is chosen to be studied and optimized numerically based on a thermoacoustic model. Firstly, the influence of key physical parameters on no-load thermodynamic performance is investigated. Then, the system output characteristics are further discussed for a better understanding of the thermoacoustic operation. According to the calculated results, it is shown that this novel thermoacoustic heat engine has the potential of realizing a compact-size and efficient system operating around 300 Hz frequency.

Development of a 5 kW traveling-wave thermoacoustic electric generator

Traveling-wave thermoacoustic heat engine is a new type of external combustion heat engine, which is capable of converting thermal energy to acoustic power with advantage of heat source flexibility, reliability and efficiency. The generated acoustic power will be further converted into electricity by connecting linear alternator with the engine. This power generation system is called traveling-wave thermoacoustic electric generator. In this paper, a new traveling-wave thermoacoustic electric generator is proposed, which consists of a multi-stage traveling-wave thermoacoustic heat engine and linear alternators. The engine has several units connected end-to-end by slim resonance tubes to obtain a traveling-wave acoustic field in the regenerator, which is required by an efficient thermoacoustic heat engine. The alternator is connected as a bypass at the end of each resonance tube. Here, a three-stage traveling-wave thermoacoustic electric generator was developed. In the experiments, the maximum electric power of 4.69kW with thermal-to-electric efficiency of 15.6% and the maximum thermal-to-electric efficiency of 18.4% with electric power of 3.46kW were achieved with 6MPa pressurized helium, 650°C and 25°C heating and cooling temperatures. Additionally, the influence of the electric capacitance on the system performance was investigated, which may provide some clue to couple the alternator with the engine. So far, this performance is the best one of such type of machines. It is believed that this technology will be suitable for many applications in the energy area, such as solar energy, industrial waste heat and so on.

A 1 kW-class multi-stage heat-driven thermoacoustic cryocooler system operating at liquefied natural gas temperature range

This article introduces a multi-stage heat-driven thermoacoustic cryocooler capable of reaching cooling capacity about 1 kW at liquefied natural gas temperature range without any moving mechanical parts. The cooling system consists of an acoustically resonant double-acing traveling wave thermoacoustic heat engine and three identical pulse tube coolers. Unlike other traditional traveling wave thermoacoustic heat engines, the acoustically resonant double-acting thermoacoustic heat engine is a closed-loop configuration consists of three identical thermoacoustic conversion units. Each pulse tube cooler is bypass driven by one thermoacoustic heat engine unit. The device is acoustically completely symmetric and therefore “self-matching” for efficient traveling-wave thermoacoustic conversion. In the experiments, with 7 MPa helium gas as working gas, when the heating temperature reaches 918 K, total cooling capacity of 0.88 kW at 110 K is obtained with a resonant frequency of about 55 Hz. When the heating temperature is 903 K, a maximum total cooling capacity at 130 K of 1.20 kW is achieved, with a thermal-to-cold exergy efficiency of 8%. Compared to previously developed heat-driven thermoacoustic cryocoolers, this device has higher thermal efficiency and higher power density. It shows a good prospect of application in the field of natural gas liquefaction and recondensation.

Numerical investigation on a 300 Hz pulse tube cryocooler driven by a three-stage traveling-wave thermoacoustic heat engine

A 300Hz pulse tube cryocooler (PTC) driven by a three-stage traveling-wave thermoacoustic heat engine (TSTHE) has been proposed and studied in this paper. In the configuration, three identical thermoacoustic heat engine units are evenly incorporated in a closed traveling-wave loop, in which three pulse tube cryocoolers are connected to the branch of each thermoacoustic heat engine. Compared with the conventional thermoacoustic heat engine which involves a traveling-wave loop and a long resonator, it has advantages of compact size and potentially high thermal efficiency. A TSTHE–PTC system was designed, optimized and studied in detail based on the thermoacoustic theory. Firstly, numerical simulation was conducted to design the system thus the optimum structure parameters of the system were obtained. With the operating condition of 4MPa mean pressure and high working frequency, a cooling power of 7.75W at 77K and an overall relative Carnot efficiency of 11.78% were achieved. In order to better understand the energy conversion characteristics of the system, distributions of key parameters such as acoustic work, phase difference, dynamic pressure, volume flow rate and exergy loss were presented and discussed. Then, the coupling mechanism of the system was investigated. In addition, influence of coupling position on the system performance was further studied.

Measurements of acoustic particle velocity in a coaxial duct and its application to a traveling-wave thermoacoustic heat engine.

We present theoretical solutions, based on linear acoustic theory, for axial acoustic particle velocity in an annular region of a coaxial duct. The solutions are expressed in terms of two non-dimensional parameters h/δ(ν) and R; h and δ(ν), respectively, represent the half of the spacing between two concentric ducts and the characteristic length given by kinematic viscosity of the gas and angular frequency of acoustic oscillations, and R is the radius ratio of the ducts. The validity of the solutions was verified by direct measurements using a laser Doppler velocimeter. The present results are applied to measurements of the acoustic power distribution in a traveling wave thermoacoustic engine with a coaxial duct, which provides experimental evidence for acoustic power feedback in the coaxial duct.

Study of a liquid-piston traveling-wave thermoacoustic heat engine with different working gases

Thermoacoustic technology is becoming increasingly attractive because of its high reliability and environmental friendliness. The double-acting traveling-wave thermoacoustic heat engine using liquid pistons, proposed by our group, can improve the thermoacoustic conversion efficiency further and yield a more compact engine. In this study, three different environmentally friendly working gases, helium, nitrogen and carbon dioxide, were studied experimentally, primarily in terms of thermoacoustic conversion parameters, including the onset temperature, the resonant frequency, and the pressure ratio, under different working mean pressures. Results show that the working gas significantly influences thermoacoustic performance. They also suggest a very encouraging application prospect for this novel thermoacoustic heat engine. Finally, we performed theoretical analysis to better understand thermoacoustic conversion with the different working gases.

Investigation on a 1 kW traveling-wave thermoacoustic electrical generator

Traveling-wave thermoacoustic heat engine is a special device capable of converting external heat to acoustic work with high reliability and high potential efficiency. By coupling with a linear alternator, it can be further developed as a new kind of electricity generator called the traveling-wave thermoacoustic electrical generator. In this paper, a prototype of 1kW traveling-wave thermoacoustic electrical generator was designed and tested. In the preliminary experiments, due to the high clearance seal loss caused by the pistons of the alternator, only 638W electric power with 16.6% thermal-to-electrical efficiency was obtained, which was far below our expectation. After further investigation, the acoustic impedance coupling relationship between the engine and alternator was first revealed by means of numerical approach. According to this relationship, the working frequency was decreased in the experiments from 74Hz to 64Hz by charging 4.5% mole fraction argon gas into the system. And a maximum electric power of 1043W with a thermal-to-electrical efficiency of 17.7% and a maximum thermal-to-electrical efficiency of 19.8% with an electric power were of 970W were obtained successfully. Other operating conditions were a mean pressure of 4.0MPa, a heating temperature of 650°C and a cooling temperature of 15°C. So far, the output electric power and efficiency are the highest values for such a thermoacoustic electrical generator. This work presents a new kind of thermal electric power generator, which is believed to be suitable for many applications in the energy area, such as solar energy, industrial waste heat and so on.

Numerical simulation and experimental investigation of a gas-liquid, double-acting traveling-wave thermoacoustic heat engine

This paper proposes a gas–liquid, double-acting traveling-wave thermoacoustic heat engine (GLDA-TWTHE), which has the advantages of both traditional thermoacoustic engine with long life span and the Stirling engine with high power density and high efficiency. By connecting three or four same thermoacoustic engines into a loop with a U-type liquid resonator, each engine can work in an ideal traveling-wave field, consequently bringing about high thermoacoustic conversion efficiency. We designed such an experimental system with about 3 kW acoustical power. The GLDA-TWTHE consists of three same thermoacoustic heat engine units and three same U-type liquid-water columns with about a diameter of 50 mm. The operating heating temperature, ambient temperature, and resonant frequency are 923 K, 303 K, and 25 Hz, respectively. Before the experiment, numerical simulation on the GLDA-TWTHE under no-load and loaded conditions was made for providing a theoretical prediction. Also, we have analyzed the influence of some parameters of the three engines being inconsistent with each other on the system performance. Finally, the experimental results were compared with the simulation, showing good agreement with each other. Based on both the theoretical and experimental results, it is found that the novel GLDA-TWTHE is a very enabling technology due to its high reliability, simple structure, and high efficiency. Copyright © 2013 John Wiley & Sons, Ltd.

Experimental investigation of a 500 W traveling-wave thermoacoustic electricity generator

In this paper, an experimental investigation of a traveling-wave thermoacoustic electricity generator, which consists of a traveling-wave thermoacoustic heat engine and a linear alternator driven by that engine, is presented. Using the results of previous theoretical and experimental research, we designed and fabricated a traveling-wave thermoacoustic heat engine and a linear alternator. In the experiments, 450.9 W of electrical power was obtained with a maximum thermal-to-electrical efficiency of 15.03%, and a maximum electrical power of 481.0 W was achieved with 12.65% thermal-to-electrical efficiency.

05/01189 Investigation on traveling wave thermoacoustic heat engine with high pressure amplitude

05/01189 Investigation on traveling wave thermoacoustic heat engine with high pressure amplitude

Investigation on traveling wave thermoacoustic heat engine with high pressure amplitude

As the thermoacoustic conversion process occurring in its regenerator is considered reversible, a traveling wave thermoacoustic engine can theoretically produce and transmit acoustic power with high efficiency. A large scale multifunction thermoacoustic engine has been designed, constructed and tested. Compared with the results of standing wave thermoacoustic heat engines, the experimental results show the engine has a lower onset temperature, much higher pressure ratio and higher efficiency. With the filling nitrogen of 0.9 MPa, the maximal pressure ratio reached 1.21, and the operation frequency was steady at 25 Hz. The single stage U type orifice pulse tube cooler driven by the engine reached 153.7 K when the working pressure was 1.5 MPa.