Investigation of a traveling wave thermoacoustic engine in a looped-tube (original) (raw)
Related papers
Numerical investigation of a looped-tube traveling-wave thermoacoustic generator with a bypass pipe
Energy Procedia
A new configuration ("a looped-tube with a bypass pipe") was recently proposed for low temperature travelling wave thermoacoustic engines and a prototype using atmospheric air as the working gas achieved an onset temperature difference as low as 65 °C. However, no further research has been reported about this new configuration to reveal its advantages and disadvantages. This paper aims to analyse this type of engine through a comprehensive numerical research. An engine of this type having dimensions similar to the reported prototype was firstly modelled. The calculated results were then qualitatively compared with the reported experimental data, showing a good agreement. The working principle of the engine was demonstrated and analysed. The research results show that an engine with such a bypass configuration essentially operates on the same thermodynamic principle as other travelling wave thermoacoustic engines, differing only in the design of the acoustic resonator. Both extremely short regenerators and a near-travelling wave resonator minimise the engine's acoustic losses, and thus significantly reduce its onset temperature difference. However, such short regenerators likely cause severe heat conduction losses, especially if the engine is applied to heat sources with higher temperatures. Furthermore, the acoustic power flowing back to the engine core is relatively low, while a large stream of acoustic power has to propagate within its resonator to maintain an acoustic resonance, potentially leading to low power density. The model was then applied to design an engine with a much longer regenerator and higher mean pressure to increase its power density. A thermoacoustic cooler was also added to the engine to utilise its acoustic power, allowing the evaluation of thermal efficiency. The pros and cons of the engine configuration are then discussed.
Numerical investigation of a looped-tube travelling-wave thermoacoustic engine with a bypass pipe
Energy, 2016
A new configuration ("a looped-tube with a bypass pipe") was recently proposed for low temperature travelling wave thermoacoustic engines and a prototype using atmospheric air as the working gas achieved an onset temperature difference as low as 65 °C. However, no further research has been reported about this new configuration to reveal its advantages and disadvantages. This paper aims to analyse this type of engine through a comprehensive numerical research. An engine of this type having dimensions similar to the reported prototype was firstly modelled. The calculated results were then qualitatively compared with the reported experimental data, showing a good agreement. The working principle of the engine was demonstrated and analysed. The research results show that an engine with such a bypass configuration essentially operates on the same thermodynamic principle as other travelling wave thermoacoustic engines, differing only in the design of the acoustic resonator. Both extremely short regenerators and a near-travelling wave resonator minimise the engine's acoustic losses, and thus significantly reduce its onset temperature difference. However, such short regenerators likely cause severe heat conduction losses, especially if the engine is applied to heat sources with higher temperatures. Furthermore, the acoustic power flowing back to the engine core is relatively low, while a large stream of acoustic power has to propagate within its resonator to maintain an acoustic resonance, potentially leading to low power density. The model was then applied to design an engine with a much longer regenerator and higher mean pressure to increase its power density. A thermoacoustic cooler was also added to the engine to utilise its acoustic power, allowing the evaluation of thermal efficiency. The pros and cons of the engine configuration are then discussed.
Traveling-wave thermoacoustic engine utilises a compact acoustic network to obtain a right time-phasing between the acoustic velocity and pressure oscillations within the regenerator to force gas parcels to experience a Stirling-like thermodynamic cycle. As such, thermal energy can be converted to mechanical work (i.e., high-intensity pressure waves). It is therefore crucial to control the time-phasing carefully to improve the performance of thermoacoustic engines. Various ways have been proposed and demonstrated for adjusting time-phasing, including both passive and active methods. The aim of this study is to introduce a new passive phase tuning method (i.e., a side-branched acoustic volume) to tune the time-phasing within a looped-tube travelling wave thermoacoustic engine. The proposed concept has been investigated both numerically and experimentally in this research. An experimental rig was simulated and designed using DeltaEC software (Design Environment for Low-amplitude ThermoAcoustic Energy Conversion). It was then constructed according to the obtained theoretical model. The result of this study showed a qualitative agreement between experimental measurement and numerical simulations, demonstrating that the proposed technique can effectively adjust the phase angle between the acoustic velocity and pressure oscillations within the loop-tube thermoacoustic engines, and improve its performance.
Applied Sciences, 2017
The performance of a thermoacoustic system that is composed of a looped tube, an engine stack, a cooler stack, and four heat exchangers, is numerically investigated. Each stack has narrow flow channels, is sandwiched by two heat exchangers, and is located in the looped tube. In order to provide a design guide, the performance of the system is numerically calculated by changing the following three parameters: the radius of the flow channels in the engine stack, the radius of the flow channels in the cooler stack, and the relative position of the cooler stack. It was found that when the three parameters are optimized, the efficiency of the engine stack reaches 75% of Carnot's efficiency and the coefficient of the performance (COP) of the cooler stack is 53% of Carnot's COP, whereas 33% of the acoustic power generated by the engine stack is utilized in the cooler stack.
Experimental investigation of an adjustable standing wave thermoacoustic engine
This work is primarily concerned with the experimental investigation of the performance of a standing wave thermoacoustic engine (TAE). The TAE technology converts thermal power into acoustic power which may be used to generate electricity or, to drive thermoacoustic cooling devices. Although there is a number of existing researches that suggest the link between the geometrical configuration of the device and its performance, there are no existing work that point out how to incorporate this aspect in the designing. Therefore, this study proposes the use of an adjustable TAE in order to alter the performance of the device while in operation. This new TAE model has an adjustable resonator length, which consisted of a 103 mm (4-in.) honeycomb ceramic stack sample, buffer volume and a cooling shell-tube heat exchanger was developed. Six different stacks were used to evaluate the performance of the TAE. Three different stack lengths (50, 100, and 150 mm), positioned at three different locations, were investigated. These locations were measured from the hot ends of the stack to the pressure antinode. In addition, the influence of the mean pressure and the working gas was investigated. Measurement of temperature difference across the stack and sound pressure levels at the steady state were used to determine the efficiency of the device. Through the adjustment of the resonator length, this study point out the benefit of choosing the best frequency so that TAE can work optimally and produce higher acoustic power.
Performance investigation and construction of a traveling wave thermo-acoustic engine
International Conference on Industrial Engineering and Operations Management, 2018
The current development of thermo-acoustic devices suggests that there is a possibility to enhance their performance even further. This technology could potentially contribute to the effort to swap conventional pollutant energy refrigerators/generators with environmental friendlier systems in the forthcoming years. The configuration of the regenerator is so far believed to be one of the factor that could contribute to the improvement the performance of the engine. This paper aims to investigate the behaviour of a designed thermo-acoustic engine when changing the porosity of the regenerator. It also aims to provide guidance on the construction, from mostly scrap and cheap materials, of a traveling wave looped-tube thermo-acoustic engine capable of generating higher sound level. The design is conducted using a code program named Design Environment for Low-Amplitude Thermo-acoustic Energy Conversion that helps to simulate in fine details the performance of the device. Three ceramic substrate blocs of different porosities have been considered as regenerators during the simulation. The results showed that the smaller porosity produced higher acoustic power. The higher performing bloc was subsequently used to develop and test a physical prototype. The constructed looped-tube thermo-acoustic engine produced a sound level of 121.4 decibel, just above the minimum auditory pain threshold.
Design and experimental investigations on a small scale traveling wave thermoacoustic engine
Cryogenics, 2013
A small scale traveling wave or Stirling thermoacoustic engine with a resonator of only 1 m length was designed, constructed and tested by using nitrogen as working gas. The small heat engine achieved a steady working frequency of 45 Hz. The pressure ratio reached 1.189, with an average charge pressure of 0.53 MPa and a heating power of 1.14 kW. The temperature and the pressure characteristics during the onset and damping processes were also observed and discussed. The experimental results demonstrated that the small engine possessed the potential to drive a Stirling-type pulse tube cryocooler.
Numerical investigation on a travelling wave thermoacoustic heat pump
Journal of Thermal Science and Technology, 2018
A thermoacoustic heat pump heater is a device having the ability to produce heat from acoustic power. The heat pump investigated was composed of an acoustic driver, a branched tube, and a looped tube. A porous component composed of many stacked steel screen meshes, called regenerator, was installed inside the looped tube. When an acoustic wave is supplied to the looped tube, filled with nitrogen gas at 0.5 MPa, heat pumping spontaneously occurs inside the regenerator. A numerical code was developed and tested. Then, the coefficient of performance was calculated for different temperatures by optimizing the regenerator flow channel radius and position inside the looped tube. It was found that the temperature affects considerably the regenerator optimum parameters.
Proceedings of Meetings on Acoustics, 2017
Investigation on acoustic radiation characteristics of an open-air traveling-wave thermoacoustic generator The acoustic radiation impedance of an Open-air Traveling-wave ThermoAcoustic Generator (OTTAG) composed of a looped tube and a resonator was theoretically described. The acoustic radiation characteristics versus different resonator types and input heating powers of this OTTAG are experimentally investigated. The comparisons of sound pressure level (SPL) at 1m far away from the open end of the resonator were carried out in an anechoic chamber, a semi-anechoic chamber and a normal laboratory under different heating power. The results showed that the difference in a normal laboratory between the anechoic chamber and semi-anechoic chamber was lower than 1.5%. The maximum SPL at 1m far away from the open end of the resonator was up to 100.1 dB ref 20μPa. This OTTAG would be used as a newly basic acoustic source for low frequency and long-range noise experiments and industrial sources and vibration.