Thermoacoustic Prime Mover Research Articles

Condensation shock induced in wet thermoacoustic prime mover

This Letter unveils a novel observation of condensation shock in a thermoacoustic prime mover with a wet stack, powered by a consistent 70 W heat input and maintained at atmospheric pressure. Intermittent pressure bursts, triggered by distinct acoustic cycles, reveal new characteristics of non-combustion-driven thermoacoustic instabilities, expanding the horizon beyond the energy conversion applications of traditional heat engines. Our findings, highlighted by pressure bursts reaching up to 35.8 kPa and detailed through time–frequency analysis, not only emphasize the critical role of phase-change dynamics but also pave the way for potential applications in heat transfer and material separation.

Simulation studies on the performance comparison of thermoacoustic prime mover with various resonator geometries and different stack materials

Simulation studies on the performance comparison of thermoacoustic prime mover with various resonator geometries and different stack materials

Numerical and Theoretical Investigations on Twin Standing-wave Thermoacoustic Prime Movers

In this work, we perform computational fluid dynamics investigations topredict the performance of the twin thermoacoustics engine (TAE) undervarious working gas/medium and at different charge pressures. The numerical model is validated by comparing with those of DeltaEC (Design Environment for Low-amplitude ThermoAcoustic Energy Conversion) predictions and previous experimental results. Additionally, the effects of (1) the geometry shape of the twin TAE and (2) different types of working gases on its performance are examined. The results indicate that the working gas/medium and charge pressure in the engine are critical to the twin thermoacoustic engine. Although the acoustic pressure amplitude is higher with air or nitrogen as the working gas, the acoustic oscillation frequency is higher with helium or argon and the value of the acoustic growth rate is larger, i.e., the limit cycle is observed growing faster in the twin TAE. Furthermore, the pressure-ratio is increased in the tapered resonator, because its velocity amplitude is decreased. It means the tapered resonator is the best choice for the twin TAE. The acoustic characteristics predicted are much closer to the experimental results than those of DeltaEC estimations, which provides a design tool for designing and predicting performances of twin TAEs.

An approach to low-temperature oscillation and high efficiency of thermoacoustic prime mover: influence of end face and reduction area of phase adjuster

The Phase Adjuster (PA) has contributed to the reduction of the onset temperature and improvement of the energy conversion efficiency of thermoacoustic systems. In this study, we investigated the performance characteristics of thin medal-shaped PAs representing the PA end faces. The results show that inserting 2 mm thick medal-shaped PAs lowered the onset temperature by 220 K. However, the insertion of thicker medal-shaped PAs maintained the onset temperature. In contrast, the energy conversion efficiency increased with the medal-shaped PA thickness. The energy conversion efficiency for 2 mm thick PAs was lower than that without PA. In addition, the thinner the medal-shaped PAs, the lower the power required for oscillation but the lower the energy conversion efficiency. These effects of the medal-shaped PA thickness indicate the necessity of different design guidelines for designing PAs for low-temperature oscillation and high efficiency in thermoacoustic systems.

Study of the reduction of the onset temperature in a loop-tube-type thermoacoustic prime mover using conical phase adjuster.—Based study on the installation position and onset temperature of conical phase adjuster

In this report, we proposed the installation of a conical phase adjuster (CPA) in a thermoacoustic prime mover as a method for reducing the onset temperature and investigated the effect of the installation position of a CPA on the onset temperature using stability analysis. The onset temperature of CPA also was investigated experimentally by changing the installation position of CPA. As a result, when CPA was installed at 1000 mm from the high-temperature end of the stack, the onset temperature was 195 K lower than the onset temperature without CPA, that is, the installation of the CPA in a loop-tube-type thermoacoustic prime mover reduced the onset temperature by 29%. Comparing onset temperatures of the PA had installed in a system, CPA is considered to have the same effect as a PA because the onset temperature tendency of the CPA to reduce at the installation position agrees with that of the PA.

3Pa4-4 Effect of medal-shaped PAs on the oscillation conditions of a thermoacoustic prime mover using stability analysis.

3Pa4-4 Effect of medal-shaped PAs on the oscillation conditions of a thermoacoustic prime mover using stability analysis.

A Traveling Wave Thermoacoustic Engine—Design and Test

Abstract The demand for clean, sustainable, and cost-effective energy continues to increase due to global population growth and the corresponding use of consumer products. The provision of heat to a thermoacoustic prime mover results in the generation of an acoustic wave that can be converted into electrical power. Thermoacoustic devices offer highly reliable and transportable power generation with low environmental impact using a variety of fuel sources. This paper focuses on the design and testing of a single-stage, traveling-wave, thermoacoustic engine. The system configuration, component design, and integration of sensors will be described. Performance testing and system analysis show that for a 300 W heat source, the thermoacoustic machine generates a 54 Hz acoustic wave with a thermal efficiency of 7.8%. The system’s acoustic power output may be increased by 84% through improved heat exchanger design. Tuning of the acoustic system and optimization of the bi-directional turbine merit attention to realize an applicable waste heat energy harvesting system.

1Pa4-1 Basic study of HPA temperature and onset temperature in thermoacoustic prime mover by stability analysis

1Pa4-1 Basic study of HPA temperature and onset temperature in thermoacoustic prime mover by stability analysis

1Pa4-2 Fundamental study on the position of CPA in a thermoacoustic prime mover using stability analysis.

1Pa4-2 Fundamental study on the position of CPA in a thermoacoustic prime mover using stability analysis.

Porous Cores in Small Thermoacoustic Devices for Building Applications

The thermoacoustic behavior of different typologies of porous cores is studied in this paper with the goal of finding the most suitable solution for small thermoacoustic devices, including solar driven air coolers and generators, which can be used in future buildings. Cores provided with circular pores, with rectangular slits and with arrays of parallel cylindrical pins are investigated. For the type of applications in focus, the main design constraints are represented by the reduced amount of the input heat power and the size limitations of the device. In this paper, a numerical procedure has been implemented to assess the behavior of the different core typologies. For a fixed input heat power, the maximum acoustic power delivered by each core is computed and the corresponding engine configuration (length of the resonator and position of the core) is provided. It has been found that cores with parallel pins provide the largest amount of acoustic power with the smallest resonator length. This conclusion has been confirmed by experiments where additive manufactured cores have been tested in a small, light-driven, thermoacoustic prime mover.

Prototype 29 m long loop-tube-type thermoacoustic prime mover

We report the performance of a prototype 29 m long loop-tube-type thermoacoustic prime mover. The phase adjuster (PA) that succeeded in low-temperature oscillation was examined for the aforementioned prototype. The onset temperature when PA length and PA position were changed was calculated using stability analysis. The onset temperature was found to be 153 °C. Using the calculation results, a prototype that succeeded in oscillating at an onset temperature of 155 °C was developed. These results indicate that the thermoacoustic system was successfully enlarged. This will promote practical application of a large system that converts waste heat to effective energy.

Numerical analysis on thermoacoustic prime mover

A two-dimensional numerical model based on compressible SIMPLE algorithm was developed to simulate the evolution process of self-excited oscillation in a thermoacoustic engine at two different heating conditions. Moreover, the performance analysis of the thermoacoustic engine was researched. On one hand, the influence of stack parameters and charge pressure on the onset temperature of self-excited thermoacoustic oscillation was exhibited and analyzed. On the other hand, the impact of different gas types on the onset temperature difference was investigated. The results indicated that the self-excited thermoacoustic oscillation happened with the same performance for both two heating conditions. The minimum onset temperature difference can be achieved when the dimensionless stack length and position are Lr = 0.055–0.06 and Xr = 0.14–0.16, respectively. For a detail, the optimal stack plate thickness is 33% of the stack channel width when the computational width is 3 times as large as the thermal penetration depth of the working gas. Furthermore, the onset temperature difference increased with the increasing of the charge pressure in prime mover. For different working gas, the onset temperature difference was the highest for argon, which was followed by helium and nitrogen. Finally, the performance was improved with the increase of the temperature difference between the two exchangers in the prime mover.

Numerical Studies of Thermo Acoustic Prime Mover on the Application of Renewable Energy

Thermo acoustic Prime Movers (TAPMs) work on the principle of conversion of heat energy to sound energy which is used to drive engine by the variation of pressure created by acoustic power. In order to develop a system theoretical knowledge about the dimension of a prime mover, working gas and operating temperature are required. This paper presents the studies of influence of working fluid in Thermoacoustic Prime mover using Delta EC software. The analysis indicates that the variation of resonant frequency, Amplitude of the acoustic wave depends on the properties of working gas(es).

1P4-7 A prototype of a thermoacoustic prime mover of the full-length 29 m -Numerical calculation of system internal diameter and onset temperature-

1P4-7 A prototype of a thermoacoustic prime mover of the full-length 29 m -Numerical calculation of system internal diameter and onset temperature-

Prediction of limit cycle amplitudes in thermoacoustic engines by means of impedance measurements

This paper deals with the prediction of the frequency and the amplitude of self-sustained oscillations generated in thermoacoustic prime movers, which are compared to measurements. A specially designed, high amplitude, acoustic impedance sensor was developed to perform measurements of the input impedance of a thermoacoustic core, as a function of the heating power supplied to the device, of the frequency, and of the amplitude of acoustic forcing. Those measurements can then be used to predict the spontaneous generation of acoustic oscillations and their saturation up to a steady-state. Those predictions were successful for various acoustic loads connected to the thermoacoustic core. Moreover, the measurements of acoustic impedance as a function of the amplitude of acoustic oscillations are compared to a model based on the linear thermoacoustic theory, and this comparison provides insights into the processes controlling the saturation of acoustic oscillations. The experimental procedure described in this paper can also have practical value, since it provides an empirical way, in principle, to optimize the coupling between the thermoacoustic core and the load so that the potential efficiency of thermoacoustic energy conversion is maximized.

Prediction of acoustic wave parameters of thermoacoustic prime mover through artificial neural network technique: Practical approach for thermoacoustics

Thermoacoustic prime movers are considered new alternative heat engines to traditional ones. For good performance of such a heat engine, a careful apparatus design is required. To predict the acoustic wave parameters responding to geometrical parameters of stack and resonator, is important for such a design. Artificial neural network (ANN) model is first proposed to predict the oscillating frequency and acoustic pressure amplitude, under given resonator length, stack length, stack plate spacing and thickness. ANN models for one standing wave thermoacoustic prime mover had been developed based on published experimental data, and evaluated based on some criteria such as least mean square error between the predicted and actual outputs during the testing phase. Concerning oscillating frequency, ANN model with the configuration of 4-4-4-1 was adopted whilst 4-4-1 for acoustic pressure amplitude, namely 4 neurons representing the four input design parameters, one or two hidden layers each with optimal four hidden neurons and one neuron representing the output oscillating frequency or acoustic pressure amplitude. Moreover, a statistical analysis has been conducted to show the contribution percentages of the proposed geometrical parameters of resonator and stack where it was found that the resonator length has the largest contribution effect with the approximate percentage of 76% on the two considered acoustic wave parameters. Compared to both experimental and DeltaEC model results, the determined ANN models had been proven to be desirable in their prediction accuracy with the error percentages of 2.26% and 0.78% for predicted oscillating frequency and acoustic pressure amplitude, respectively. This research work provides a promising practical modeling approach based on ANN technique for complex design problems in thermoacoustic systems.

Experimental and theoretical study of density fluctuations near the stack ends of a thermoacoustic prime mover

This paper proposes the experimental and theoretical study of nonlinear heat transport processes generated by large amplitude acoustic oscillations at the ends of a stack of plates in the presence of a temperature gradient. These processes are notably involved in the operation of thermoacoustic engines. The measurement method, a time-resolved and full-field digital holography interferometry technique, enables to measure the density fluctuations from the optical phase difference between two laser beams. This technique is applied to the analysis of density fluctuations in the vicinity of a stack submitted to a temperature gradient, firstly for the case of (uncontrolled) self-sustained acoustic oscillations generated spontaneously in a standing wave thermoacoustic prime mover, and secondly for the case of an assigned acoustic field whose amplitude is controlled by an external sound source. A theoretical model describing the advective heat transport by sound at the ends of the heated stack is also presented, and numerical simulations are then carried out. The comparison between experimental data and numerical simulations is provided for several stack positions, several sound pressure levels, and several amounts of heat supplied to the stack, and the results show good agreement between the experiments and the model.

Experimental study on the effect of hydraulic radius of stack on the performance of thermoacoustic prime mover with open resonator

<p class="Abstract">Thermoacoustic prime mover is a device which converts thermal energy into acoustic work. The device mainly consists of a resonator pipe, a stack (a porous medium), and two heat exchangers. Four stacks were made of a pile of stainless wire-mesh screens with various mesh numbers of #12, #14, #16, and #18, providing the effective hydraulic radius of 0.32 mm, 0.28 mm, 0.25 mm, 0.23 mm, respectively. Each stack has 4 cm length. By using the wire-mesh screens, it is easier to vary the hydraulic radius of stack than any other material. The stack is sandwiched between a hot heat exchanger and an ambient heat exchanger. The resonator is made of a stainless-steel pipe with one end open and the other closed. The stack and heat exchangers are placed inside a resonator pipe near the closed end. The thermal energy were provided by using an electric heater which is installed at the hot heat exchanger. Ambient water was flowing through the ambient heat exchanger. Sound is produced by the stack when the temperature difference between the both ends of stack reachs an onset point. This experiments were performed by recording the temperatures at both ends of stack and the pressure amplitudes of the sound at several points along the resonator for various hydraulic radius of stack. It is found that the effective hydraulic radius of 0.28 mm gives the lowest onset temperature, the shortest time to reach onset condition, and the highest pressure amplitude which are 314°C, 299 s, and 2.89 kPa, respectively. The frequency of sound is not altered by the change of hydraulic radius of stack.</p>

CFD Simulation of Twin Thermoacoustic Prime Mover for Binary Gas Mixtures

The objective of the present simulation is to analyze the performance of a twin thermoacoustic prime mover using CFD in terms of frequency and pressure amplitude. Pure fluid media such as helium, argon, nitrogen and their binary gas mixtures are studied at a constant operating pressure of 5 bar. The GAMBIT 2.3.16 pre-processor is used for creating the geometry of twin prime mover and the CFD package FLUENT 6.3 is used for simulating the device with different combinations of gas mixtures. The geometrical parameters and temperature gradients across the stack are kept constant throughout the simulation. It is found that the pressure amplitude of the thermoacoustic oscillations is higher for pure argon, whereas the frequency of the oscillations is higher for helium (495 Hz) rather than other gases and mixtures.

Experimental Study of Resonance Frequency at Prime Mover Thermoacoustic Standing Wave

<p class="Abstract">Thermoacoustic prime movers work by using thermal energy to produce acoustic energy in the form of sound wave through thermoacoustic effect which occurs in a porous medium called stack. This paper describes an experimental study on the relation between the order of resonance frequencies generated by a thermoacoustic prime mover and the length of the resonator and the viscous penetration depth. Extending the resonator length will decreasing the resonance frequency which result in the increasing in the viscous penetration depth. Generally, the generated sound consists of only one frequency, that is the first-order one. However, under certain conditions, the sound has only the second-order frequency or comprises two frequencies of the first-order and second-order resonance frequencies. This phenomenon can be explained by considering the comparison between the effective hydraulic radius of stack () and the viscous penetration depth (). It is found that the first-order frequency appears when , while when (with calculated by using the first-order frequency) then the second order frequency is produced so that is back to a smaller value and therefore the condition of is recovered. In addition, when of the thermoacoustic prime mover will<em> </em>generate the first and second order frequencies together.</p>