Thermoacoustic Electricity Generator Research Articles

Low-cost cascade thermoacoustic electric generator for energy harvesting

The cascade thermoacoustic heat engine has garnered significant attention for its ability to convert various heat sources into acoustic power without the challenges of acoustic streaming. By integrating it with a commercial loudspeaker, it can be further developed into a novel, low-cost thermoacoustic electric generator. This study aims to design and evaluate a thermoacoustic electric generator capable of producing several watts of electricity. The system consists of a cascade thermoacoustic engine, comprising a standing-wave and a traveling-wave unit, coupled with a B&C 6PS38 loudspeaker in a linear configuration. Atmospheric air is used as the working fluid, and standard market components, such as PVC and steel pipes, are proposed to minimize costs. Unlike traditional thermoacoustic generators, this system uses commercially available loudspeakers and a linear configuration, offering a cost-effective solution for low-wattage power generation, free from the issue of acoustic streaming. This makes it suitable for small-scale, distributed energy systems. The numerical simulation tool DeltaEC is employed to design and assess the system's performance. The optimal configuration is 4 m long, with the standing-wave and traveling-wave units centrally positioned. Operating at a frequency of 74.56 Hz, the system generates 90.18 W of electrical power with a total heat input of 1046.74 W and an external load resistance of 19.77 ohms. This corresponds to a heat-to-acoustic efficiency of 18.41 %, an acoustic-to-electric efficiency of 68.98 %, and an overall heat-to-electric efficiency of 8.62 %. The study also emphasizes the importance of operating conditions and impedance matching between the cascade engine and the loudspeaker. These findings represent progress toward developing an affordable thermoacoustic generator for energy recovery and other applications.

Operation map of a traveling-wave thermoacoustic electric generator with variable resistive-capacitive electric loads.

A toroidal-topology traveling-wave thermoacoustic electric generator (TWTEG) is developed. It consists of a traveling-wave thermoacoustic engine, two linear alternators connected in parallel, and sets of variable resistive-capacitive (R-C) external electric loads, in conjunction with accessories and instrumentation required for experimental investigations. The working medium is helium with a static absolute pressure that varies from 25 bars to 30 bars. A detailed description of the thermal design of the heat exchangers is presented. Sustainable operation of the TWTEG is achieved over a range of external R-C loads at different imposed hot-side temperatures and mean gas pressures. The performance parameters are measured for different experimental conditions and compared with a developed lumped-element model. The comparison between the experimental results and predictions reveals a good agreement. The impedance matching between the thermoacoustic engine and the linear alternators is investigated experimentally over a wide range of external R-C loads. The external R-C loads play a crucial role in the operation of the TWTEG. The mean gas pressure changes the operating frequency; however, it has no significant influence on the operating range of the TWTEG on the R-C load map. Increasing the hot-side temperature improves the thermal-to-acoustic efficiency and extends the operating region into larger regions.

Influence of length of resonance tubes on multi-stage looped thermoacoustic electric generator

Resonance tubes are often used to connect multi-stage looped thermoacoustic heat engine and linear alternators to form a multi-stage looped thermoacoustic electric generator. In this paper, we experimentally investigate the performance of a multi-stage looped thermoacoustic electric generator with two sets of resonance tubes of different lengths. With the increase of the length of resonance tubes from 1.5 m to 2 m, the system frequency decreases from 70 Hz to 62 Hz. The maximum output acoustic power increases from 6.97 kW to 8.16 kW, and the maximum output electric power increases from 5.09 kW to 6.24 kW. Meanwhile, the maximum thermoacoustic efficiency increases from 23.08 % to 23.94 %, the maximum acoustic-to-electric efficiency increases from 78.03 % to 82.06 % and the maximum thermal-to-electric efficiency increases from 17.79 % to 19.64 %. Numerical simulation is also conducted based on a 3-step coupling method and validates the experimental results. This study demonstrates that adjusting the length of resonance tubes in a multi-stage looped thermoacoustic electric generator is an effective way to tune the frequency as well as to improve the coupling between the multi-stage looped thermoacoustic heat engine and linear alternators.

Construction and testing of small-scale thermoacoustic electricity generator with different heating power

The necessity of renewable energy is indispensable. Nowadays, researchers focus on converting waste or solar heat into advantageous energy, such as electric energy, using thermoacoustic scientific knowledge. The thermoacoustic machine converts the heat energy into sound energy and conversely. Then, using a linear alternator, it converts into electric energy. In this study, we focus on the construction and testing of small-scale thermoacoustic electricity generators with different heating temperatures. The heat is converted into acoustic energy employing the thermoacoustic engine, and the acoustic energy is converted into electrical energy using the linear alternator. In this investigation, the heating power varies from 226-389 W. The result shows that 32.2 mW of electricity was found as the thermal power at 389 W. Moreover, the onset heating temperature span is 316?C.

Time-domain acoustic-electrical analogy investigation on a high-power traveling-wave thermoacoustic electric generator

Thermoacoustic electric generator is a novel heat-to-power conversion technology with potential high efficiency and reliability, showing great potential in distributed power generation. In this paper, we conduct time-domain acoustic-electrical analogy investigations on a high-power 4-stage looped traveling-wave thermoacoustic electric generator to shed lights on the system performance. The components of a thermoacoustic system are simplified as an acoustic–electrical analogy model, thus saving computational time. Additionally, the nonlinear effects in the regenerator, heat exchanger and resonance tube are considered in establishing the time-domain equations. Method validation shows a reasonable agreement between experimental and simulated results. Transient evolutions of the oscillating pressure and volume flow rate are firstly given. Investigation is then conducted on onset temperature using different working gases of helium, argon, nitrogen, and neon. The results indicate that when the external resistance reaches 70 Ω, the minimum onset temperature difference of 112 K can be achieved with argon as the working gas. For steady-state characteristics, the influences of electric resistance and heating temperature are explored. It is found that higher heating temperature contributes to larger electric power. A large electric resistance results in a large electric resistance at high heating temperature, while the highest efficiency is achieved with a medium electric resistance. Furthermore, higher heating temperature can lead to more irreversible losses. With helium employed, a maximum electric power of 13.3 kW with thermal-to-electric efficiency of 27.4% is achieved with an electric resistance of 150 Ω and a heating temperature of 950 K, and a highest thermal-to-electric efficiency of 33.5% with electric power of 1.38 kW is obtained when the electric resistance and heating temperature are 90 Ω and 750 K, respectively. This study shows that the proposed method provides a new perspective and an effective method for understanding thermoacoustic electric generator.

Numerical and experimental research on a high-power 4-stage looped travelling-wave thermoacoustic electric generator

Looped travelling-wave thermoacoustic electric generator (LTTAEG) can transform thermal energy to electric power using thermoacoustic effect. Based on our previous effort on multi-stage LTTAEG with side-branched and dual-opposed linear alternators (LAs) as acoustic-to-electric transducers, for a higher output electric power and thermal-to-electric efficiency, a 4-stage LTTAEG is studied numerically and experimentally in this paper. In the simulation, the performance of 4-stage looped thermoacoustic heat engine is investigated based on linear thermoacoustic theory while the performance of dual-opposed LA is studied based on a novel network model. A new coupling algorithm between the 4-stage looped TAHE and dual-opposed LA is also proposed. In experiment, with 6 MPa pressurized helium as working gas, 650 °C and 25 °C heating and cooling temperatures. A highest electric power of 6.1 kW with thermal-to-electric efficiency of 15.86% and a highest thermal-to-electric efficiency of 19.64% with electric power of 4.37 kW is obtained when the electric capacitance connected to the LA is 17 μF and the electric resistance is 40 Ω and 75 Ω, respectively. Due to the high oscillating pressure in the system, some nonlinear phenomena have caused the simulation results deviated from the experimental results, especially in acoustic power and electric power, which should be investigated and considered in the future study.

Asymmetrically heated multi-stage travelling-wave thermoacoustic electricity generator

Recent developments of thermoacoustic engines have demonstrated that thermoacoustic technology is a viable option for waste heat recovery and low-cost electricity generation, Thermoacoustic technology is capable of converting low-grade heat to electrical power with only one moving part. Great reliance has been placed on evenly heated cores of multistage thermoacoustic engines, whatever the acoustic impedance is within the engine's core. This article proves that the unbalanced acoustic impedance within the cores can be effectively matched by using the asymmetric heat method. Accordingly, the thermoacoustic efficiency can be increased. DeltaEC code was employed to perform the numerical calculations and laboratory measurements were then taken to confirm the concept and validate the numerical model. Both numerical and experimental data show an increase in loop acoustic power with this new technique. DeltaEC simulation predicted an increase in the electrical power output from 24.4 W to 31.4 W, when heat supplied into the system went from (50%:50%) to a 40%:60% ratio, which matched an increase from 16.5 to 23 W in the experiments with no other change in the design except asymmetric heat input. DeltaEC results have implied that there is an optimal ratio of 30%:70%. It was also seen in the DeltaEC that the overall onset temperature decreased by about 40 °C for larger asymmetrical ratios of heat input, which is advantageous for this application.

Design Optimization and Performance Analysis of a Multi-Kilowatt Thermoacoustic Electric Generator Using DeltaEC Model

AbstractWaste heat recovery from power plants and industries requires a new type of electricity generator and related technological developments. The current research work is aimed at the design of a multi-kilowatt thermoacoustic electric generator, which can be employed as the bottoming cycle of a gas turbine power plant or for industrial waste heat recovery. The proposed device converts thermal energy into acoustic power and subsequently uses a piezoelectric alternator to convert acoustic power into electricity. The challenge in designing such a device is that it has to be acoustically balanced. The performance of the device is greatly affected by numerous parameters such as frequency of the traveling acoustic wave, heat exchanger parameters, regenerator dimensions, and acoustic feedback loop. The proposed device is a lab-scale demonstration targeted to produce few kilowatts of electric power from a 20 kWth heat source. DeltaEC software is used to achieve the acoustically balanced configuration of the device. The DeltaEC model outcomes are used to arrive at the optimized design of the device and its components. The analytical method, the optimized geometrical dimensions of thermoacoustic components, and the minimum required conditions of heat source input are presented in this paper.

Development of a Multi-Stage Configuration for Electricity Generation Using Thermo-Acoustic Approach

This work describes the development and assessment of a three-stage thermo-acoustic electricity generator that demonstrate the potential of conversion of waste heat into useful electricity. A three-stage travelling-wave thermo-acoustic system was constructed and tested. The effect of the heat source on the potential of the device to generate electric power is analysed. Theloudspeakerhad used for the acoustic-to-electricity conversion in this research study. The onset temperature difference, the onset time,and the magnitude of the electricity generated has considered as the performance indicators of the device developed. This paper provides details of the experimental investigation that consists of measuring the temperatures, the frequency of the sound-wave, and the acoustic power generated using thermocouples and sound level meter coupled to data acquisition for signal processing and visualization. Electric power supplied to the cartridge heaters at a maximum voltage range of 150 to 190 Volts. The effect of the geometrical configuration of the device concerning acoustic-to-electricity with electricity conversion is analysed. The best geometrical arrangement for generating electricity at the lowest onset temperature difference had identified.The three-stage travelling-wave system generated the highest output voltage of approximately 2.4 V.

Numerical and experimental study of a looped travelling‐wave thermoacoustic electric generator for low‐grade heat recovery

Thermoacoustic technology has drawn increasing attention due to its advantages such as reliability and environmental benignity. Aiming at low-grade heat recovery, we developed a travelling-wave thermoacoustic electric generator consisting of a looped travelling-wave thermoacoustic engine and a linear alternator. In order to explore the operating characteristics of the electric generator, we numerically analyzed the acoustic field characteristics with a modified model. The analysis shows that high acoustic impedance appears in all three stages, and the travelling-wave component dominates the acoustic field of the loop, which is significant for both thermoacoustic conversion and acoustic power propagation. Furthermore, we also investigated the effects of external electric compliance, resistance, and hot end temperature on the output electric power, thermal-electric efficiency, and other related parameters. In the experiments, a thermal-electric efficiency of 3.7% with an output electric power of 24 W has been achieved, when the hot end temperature is 120°C. The relative Carnot efficiency can exceed 14% when the hot end temperature is between 120°C and 190°C. The promising results demonstrate the significant potential of thermoacoustic electric generation in low-grade heat recovery.

Development and Assessment of Two-Stage Thermoacoustic Electricity Generator

This paper presents the development and assessment of a two-stage thermoacoustic electricity generator that aims to mimic the conversion of waste heat from the internal combustion engine exhaust gases into useful electricity. The one wavelength configuration consists of two identical stages which allow coupling a linear alternator in a “push-pull” mode because of the 180° out of phase acoustic excitation on two sides of the piston. This type of coupling is a possible solution for the low acoustic impedance of looped-tube traveling-wave thermoacoustic engines. The experimental set-up is 16.1 m long and runs at 54.7 Hz. The working medium is helium at maximum pressure of 28 bar. In practice, the maximum generated electric power was 73.3 W at 5.64% thermal-to-electric efficiency. The working parameters, namely load resistance, mean pressure and heating power, were investigated. System debugging illustrates the effect of local acoustic impedance of the regenerator on the start-up process of the thermoacoustic engine. The additional modelling showed that the feedback loop length can be reduced by using a combination of acoustic inertance and compliance components.

Two-stage travelling-wave thermoacoustic electricity generator for rural areas of developing countries

Thermoacoustic heat engines convert thermal power into acoustic power with no-moving parts, while the latter can be converted to electricity using linear alternators. Such thermoacoustic electricity generators can be a means of providing inexpensive electricity to developing countries using the simplest fabrication approaches. This paper shows a detailed study of a prototype waste-heat-driven, two-stage, looped-tube, travelling-wave thermoacoustic electricity generator with a branched linear alternator and tuning stub for acoustic impedance matching purposes. The generator was modelled and designed using DeltaEC. To keep the costs down, the working medium was atmospheric air, many resonator components were made of PVC pipes and fittings, heat exchangers were made of automotive parts, while the linear alternator was a commercially available loudspeaker. The prototype generated 14.2 W of electrical power to a load of 9 Ω. The effects of matching stub length, variable resistive loads and heat inputs were investigated. The simulations and measurement results are presented and discussed in detail.

Experimental investigations of the performance of a thermoacoustic electricity generator

This paper presents the experimental investigation of a two-stage thermoacoustic electricity generator able to convert heat at the temperature of the exhaust gases of an internal combustion into useful electricity. The novel configuration is one wavelength and consists of two identical stages. The identical stages will have out of phase acoustic wave at similar amplitudes which allows coupling a linear alternator to run in push-pull mode. The experimental set-up is 16.1 m long and runs at 54.7 Hz. The working medium is helium at 28 bar. The maximum generated electric power is 73.3 W at 5.64% thermal-to-electric efficiency. The working parameters including load resistance, mean pressure and heating power were investigated.

Design and construction of a two-stage thermoacoustic electricity generator with push-pull linear alternator

Travelling-wave thermoacoustic heat engine is capable of converting heat to acoustic power which in turn can be used to generate electricity by a linear alternator. The thermoacoustic heat engine can work in a wide range of heat quality, giving it the ability to be used for waste heat recovery. In this paper, a new configuration of looped-tube travelling wave thermoacoustic engine is proposed, which consists of two identical stages each having a power extraction point, and the linear alternator connecting these two points working in “push-pull” mode. This enables a more effective acoustic impedance matching compared to the use of multiple linear alternators known in the literature. The laboratory demonstrator has been designed, built and tested. The applied heat source temperature is similar to that of the internal combustion engine exhaust gases in order to explore the potential of using the device for waste heat recovery from road or marine transport. In experiments, the maximum electric power of 48.6 W at thermal-to-electric efficiency of around 6% was achieved with helium at 28 bar as working fluid and 297 K temperature difference across the regenerator. The performance of the device has been analysed and compared to modelling performed using DeltaEC simulation tool.

Numerical investigation of a looped-tube traveling-wave thermoacoustic generator with a bypass pipe

In this paper, based on the recent development of looped-tube thermoacoustic engine with a bypass pipe, we propose and numerically demonstrate a travelling wave thermoacoustic electric generator using this configuration. It essentially employs a one wave-length travelling-wave acoustic resonator which has low acoustic losses. The engine branch consists of a compliance, a inertance tube, an engine core, and an alternator. An ultra-compliant alternator (i.e., a sub-woofer) is installed in the acoustic compliance section where the local acoustic impedance is relatively low but the cross sectional area is big. The numerical simulations demonstrate its working principle, and show that it can potentially achieve comparable performance as other types of travelling wave thermoacoustic electric generators.

Development of a three-stage looped thermoacoustic electric generator capable of utilizing heat source below 120 °C

Thermoacoustic engine, with the outstanding characteristics of high reliability and environmental benignity, is one of the most attractive and promising energy conversions to recover low-grade thermal energy. In this paper, a three-stage looped thermoacoustic electric generator, consisting of a three-stage looped thermoacoustic engine and a linear alternator, was proposed and built. To obtain a better coupling between the thermoacoustic engine and the linear alternator, the acoustic impedance of the linear alternator has been adjusted by modulating the external electric resistance/compliance and the frequency. The frequency was adjusted by adopting the He-Ar mixture. Additionally, the location and the length of compliance tube have been optimized to improve the acoustic field in the system. Upon optimization, a maximal thermal-to-electric efficiency of 1.51% can be achieved at the hot temperature of 120 °C with He-Ar mixture as the working fluid, in which the mole fraction of helium was 0.63. Furthermore, the system has also been tested in the hot temperature range of 90 °C–200 °C. Results show that the thermal-to-electric efficiency stabilizes at around 1.5% when hot temperature is in the range of 120 °C–170 °C.

Design issues and performance analysis of a two-stage standing wave thermoacoustic electricity generator

This paper is concerned with the study of low-cost low-power thermoacoustic electricity generators. Based on a target electrical output power of 100W, a two-stage standing wave prototype integrating a commercial loudspeaker in side branch arrangement is conceived. Each stage consists of a square-pore stack sandwiched between hot and ambient heat exchangers. The working gas is air at atmospheric pressure oscillating at the operation frequency of 194.5Hz. Design issues and optimization procedures are discussed in detail. The prototype efficiency in converting heat to electrical power is simulated by the specialized design tool DeltaEC based on the linear theory of thermoacoustics. Computations reveal that at the heating temperature of 527°C the target electrical output power is extracted by the loudspeaker with an acoustic-to-electric efficiency of around 70% and that the overall thermal-to-electrical conversion efficiency of the engine is 5.7%. This result suggests that in applications involving the use of loudspeakers as linear alternators and air at near atmospheric pressure as working fluid, electricity generators of the standing wave type could perform, comparably to their travelling-wave counterparts. This is likely due to a simpler design of the alternator-engine coupling and a simpler and more compact configuration.

Acoustic matching of a traveling-wave thermoacoustic electric generator

Acoustic impedance matching is critical to the overall performances of a traveling-wave thermoacoustic electric generator. This paper presents an effective approach for matching the acoustic impedances of the thermoacoustic engine and the linear alternators for maximizing the output electric power and thermal-to-electric efficiency. The acoustic impedance characteristics of the engine and the linear alternators are analyzed separately, and the methods for modulating the acoustic impedances are investigated numerically. Specially, two different coupling locations including one at the resonator and the other one at the loop of the thermoacoustic engine are compared. It is found that the imaginary part of the load acoustic impedance should be near zero for a good output performance of the engine at either coupling location. The real part of the optimal acoustic impedance for the coupling location at the resonator is smaller than that for the one at the loop. The acoustic impedance of the linear alternator can be simply and effectively adjusted to the expected range by tuning the operating frequency, load resistance and the electric capacitance. Both the experiments and numerical simulations show that a better matched condition can be achieved when they are coupled at the location at the resonator. Maximum output electric power of 750.4W and the highest thermal-to-electric efficiency of 0.163 have been achieved. When they are coupled at the loop, the maximum electric power and the thermal-to-electric efficiency become 506.4W and 0.146 due to the lower quality of the acoustic matching. The acoustic matching approach presented in the paper would be helpful for guiding the designs of thermoacoustic/alternator and compressor/cryocooler systems.

An acoustically matched traveling-wave thermoacoustic generator achieving 750 W electric power

TWTEG (traveling-wave thermoacoustic electric generator) is promising in efficiently converting the heat of fuel combustion, solar energy, industrial waste heat, etc. into electricity with a very scalable power output. Based on the decoupling method and theoretical analysis, the acoustic impedance requirements of the TWTE (traveling-wave thermoacoustic engine) and LAs (linear alternators) to reach an efficient and powerful operation state were studied quantitatively. A 1 kW level traveling-wave thermoacoustic electric generator was then built for experimental study. Good matching conditions of acoustic impedances were then experimentally demonstrated by modulating the working frequency, load resistance, and electric reactance of the thermoacoustic electric generator, which agreed well with the theoretical analysis. A maximum electric power output of 750.4 W and a highest thermal-to-electric efficiency of 0.163 have been achieved by the acoustically matched thermoacoustic electric generator with helium of 3.16 MPa as the working gas. This work would be instructive for the acoustic matching and designs of high-performance thermoacoustic electric generation systems.

A novel method for improving the performance of thermoacoustic electric generator without resonator

A thermoacoustic electric generator without resonator designed for aerospace application is discussed in this study, which is developed by a traveling-wave looped-tube thermoacoustic heat engine coupling with two linear alternators directly. A novel method of filling phase modulation object in the acoustic power output port is proposed to improve the performance of the thermoacoustic electric generator. The experimental results show that the ellipsoid makes the most significant influence among sphere, cylinder and ellipsoid serving as phase modulation object. Varying the major axis of the ellipsoid only, the influence of it increases first and then decreases. The ellipsoid fixed in different positions makes different effects. The maximum output electric power of 73.31W and the maximum system efficiency of 14.12% are obtained in the upper and middle positions respectively.