非对称双级环路行波热声热机的实验研究*

对于双级环路行波热声热机,两个热声核的相对位置直接影响到其起振温度,而热声热机的起振温差决定了其可利用的热源品位。基于线性热声理论分析,通过改变两个热声核的相对位置,研究了两个热声核的相对位置改变对其起振温差、压力振幅和压比等的影响。结果表明,双级环路行波热声热机的起振温度随着两个热声核从中心对称位置逐步靠近时先下降再上升,当两个热声核之间的谐振管长度比例为1:3.5时,系统获得最小的起振温差为59.6℃（工质为N₂,充气压力为2.5 MPa）。在相同温差下,该系统在谐振管长度比例为1:3.5的位置相较于其他位置具有较大的压力振幅和压比。     

Performance of an air-cooled looped thermoacoustic engine capable of recovering low-grade thermal energy

An air-cooled looped thermoacoustic engine is designed and constructed, where an air-cooled cold heat exchanger (consisting of copper heat transfer block, aluminum flange, and aluminum fin plate) is adopted to extract heat and the resonant tube is spiraled and shaped to fit to the available space. Experiments have been conducted to observe how onset temperature difference and resonant frequency are affected by mean pressure, working fluid, and diameter of compliance tube. Besides, the influences of temperature difference, mean pressure, working fluid and diameter of compliance tube on pressure amplitude, output acoustic power, and thermal efficiency of the system have been investigated. The air-cooled looped thermoacoustic engine can start to oscillate at a lowest temperature difference of 46°C, with the working fluid of carbon dioxide at 2.34 MPa. A highest output acoustic power obtained is 6.65 W at a temperature difference of 199°C, with the working gas of helium at 2.58 MPa, and the thermal efficiency is 2.21%. This work verifies the feasibility of utilizing low-grade thermal energy to drive an air-cooled looped thermoacoustic engine and extends its application in the water deficient areas.     

Thermodynamic analysis of onset characteristics in a miniature thermoacoustic Stirling engine

This paper analyzes the onset characteristics of a miniature thermoacoustic Stirling heat engine using the ther-modynamic analysis method. The governing equations of components are reduced from the basic thermodynamic relations and the linear thermoacoustic theory. By solving the governing equation group numerically, the oscillation frequencies and onset temperatures are obtained. The dependences of the kinds of working gas, the length of resonator tube, the diameter of resonator tube, on the oscillation frequency are calculated. Meanwhile, the influences of hydraulic radius and mean pressure on the onset temperature for different working gas are also presented. The calculation results indicate that there exists an optimal dimensionless hydraulic radius to obtain the lowest onset temperature, whose value lies in the range of 0.30 0.35 for different working gases. Furthermore, the amplitude and phase relationship of pressures and volume flows are analyzed in the time-domain. Some experiments have been performed to validate the calculations. The calculation results agree well with the experimental values. Finally, an error analysis is made, giving the reasons that cause the errors of theoretical calculations.     

以氦气为工质的行波热声发动机研究

随着对热声热机研究的深入，特别是行波热声发动机概念的提出，热声发动机效率得到了质的提高。为了实现热声发动机与制冷机的良好匹配，以氦气为工质时热声发动机需具有较低的起振温度、较大的压力波强度、较好的单频率特性。本文对自行研制的新型热声发动机进行了深入研究，以氦气为工质，在充气压力为2．0MPa时获得了1．19的压比，系统频率稳定在约73Hz，为利用新型热声发动机驱动脉管制冷机或其它热声制冷机创造了有利条件。此外，该热声发动机起振温度较低，初步具备了利用工业废热等低品位能源驱动的条件。     

An electret-based thermoacoustic-electrostatic power generator

This study reports a new concept for power generation from thermal energy, which integrates a thermoacoustic engine (TAE) with a contact-free electret-based electrostatic transducer. The TAE converts thermal energy into high-intensity acoustic energy, while the electret-based electrostatic transducer converts the generated acoustic energy into electricity. The experiments demonstrate the feasibility and potential of the proposed electret-based thermoacoustic-electrostatic power generator (TAEPG). The dynamic response of the electrostatic transducer and energy conversion inside the TAE are further investigated using a lumped element model and a frequency-domain reduced-order network model. Good agreement is achieved between experimental measurements and theoretical predictions. Furthermore, a parametric study is performed to study the effect of key parameters including the external heating power, air gap, and resistive load on the performance of the TAEPG. Results show that an open-circuit voltage amplitude of 4.7 V is produced at a closed-end pressure amplitude of 480 Pa in the experiment, and it is estimated that 25.2% of the acoustic power generated by the TAE has been extracted by the electret-based electrostatic transducer. In this case, the maximum electric power output is measured to be 2.91 μW at a resistive load of around 2.2 MΩ. By increasing the external heating power, the TAEPG can produce a maximum voltage amplitude of 8 V. This work shows that the proposed concept has great potential for developing miniature heat-driven power generators.     

CFD simulation of a thermoacoustic engine with coiled resonator

Thermoacoustic energy conversion is based on the Stirling cycle. In their most basic forms, thermoacoustic devices are comprised of two heat exchangers, a porous medium, both placed inside a resonator. Work is created through the interaction of strong sound waves with the porous medium that is subject to external heating. This work explores the effect of resonator curvature on the thermoacoustic effect. A CFD analysis of a whole thermoacoustic engine was developed and the influence of a curved resonator on the thermoacoustic effect is discussed. The variation of pressure amplitude and operating frequency serves as metrics in this investigation. It was found that the introduction of curvature affects the pressure amplitude achieved. Severely curved resonators also exhibited a variation in operating frequency.     

流动阻力损失对斯特林热机功率和效率影响的理论分析

目前对斯特林热机的理论热工分析主要集中在热阻、热漏和回热损失对效率和功率的影响。讨论了在加进流动阻力损失后,对斯特林热机功率和效率的影响,并对功率和效率曲线进行了理论模拟。     

Performance of solar powered thermoacoustic engine at different tilted angles

In this study, the thermodynamic performance of a thermoacoustic engine charged with different working fluids were examined at different tilted angles ranging from ?90° to 90° with 45° angular interval. The results suggest that the influence of the tilted angle on the onset temperature of the engine depends on the viscidity of the working gas. The lower the viscidity is, the more obvious the influence is. The difference between the maximum and the minimum onset temperature of the engine charged with nitrogen could be as high as 52 °C, but the difference for system charged with helium is only about 1.5 °C. The tilted angle has little or no effect on the pressure oscillation amplitude, pressure ratio, resonance frequency and the relation of the temperature versus heat power. They are mainly affected by the properties of the working gas. Furthermore, the interactions of the oscillatory motion and the natural convection of the working gas within the thermoacoustic core were also examined. The properties are of importance for the thermoacoustic engine driven by two-axis solar collector, for the tilted angle of the engine varies with the sun position.     

斯特林发动机绝热分析法研究

对斯特林发动机绝热分析法进行了详细的阐述,对GPU-3型和P-40型斯特林发动机进行了绝热分析。收集了NASA Lewis研究中心的GPU-3型和P-40型斯特林发动机不同工况下的一系列实验测试数据,通过绝热分析法计算数据和实验测试数据的对比可知：斯特林发动机绝热分析法计算的轴功率、吸热量均偏大。轴功率的计算误差随着转速的增加而增大,随着压力的增加而减小。吸热量的计算误差随着转速的增加而增大。绝热分析法计算误差主要是由于没有计算机械损失、发动机漏气损失以及没有考虑非定常的交变流动的影响造成的。     

斯特林热机冷热电联产系统的可行性分析

斯特林热机对于促进能源的综合利用、减少环境污染具有重要的意义。文中通过对斯特林热机的斯特林循环及其热效率的分析,提出了三种不同形式的以斯特林热机为动力源的分散式冷热电三联产系统,并分别对其进行经济性分析。通过综合对比分析得出基于斯特林热机的分散式冷热电三联产是我国未来能源系统发展的一种环保的经济的选择。     

Design and experimental validation of looped-tube thermoacoustic engine

The aim of this paper is to present the design and experimental validation process for a thermoacoustic looped-tube engine.The design procedure consists of numerical modelling of the system using DELTA EC tool,Design Environment for Low-amplitude ThermoAcoustic Energy Conversion,in particular the effects of mean pressure and regenerator configuration on the pressure amplitude and acoustic power generated.This is followed by the construction of a practical engine system equipped with a ceramic regenerator-a ...     

Novel Helmholtz resonator used to focus acoustic energy of thermoacoustic engine

A thermoacoustic engine (TE) converts thermal energy into acoustic power without any mechanical moving parts. It shows several advantages over traditional engines, such as simple configuration, stable operation, and environment-friendly working gas. In order to further improve the performance of a thermoacoustically driven system, methods are needed to focus the acoustic energy of a TE to its load. By theoretical analysis based on linear thermoacoustics, a novel Helmholtz resonator is proposed to increase the transmission ability of a TE, which makes full use of the interaction between inertance and compliance effects. With this configuration, the output pressure amplitude of a TE is amplified and the maximal pressure amplitude can occur at the end of the Helmholtz resonator tube with a length much shorter than 1/4 wavelength. Furthermore, the Helmholtz resonator has shown remarkably increased volume flow rates at both ends. In experiments, a Helmholtz resonator amplifies the pressure ratio from 1.22 to 1.49 and produces pressure amplitude of 0.44 MPa with nitrogen of 2.2 MPa as working gas. Relatively good agreements are obtained between computational and experimental results. This research is instructive for comprehensively understanding the transmission characteristics of acoustic components.     

Influence of acoustic pressure amplifier dimensions on the performance of a standing-wave thermoacoustic system

A standing-wave thermoacoustic engine, employing an acoustic pressure amplifier (APA), is simulated with linear thermoacoustics to study the influence of APA’s dimensions on performance of the thermoacoustic system. Variations of operating parameters, including pressure ratio, acoustic power, hot end temperature of stack etc., versus length and diameter of APA are presented and discussed based on an analysis of pressure and velocity distribution in APA. Simulation results indicate that a largest amplification effect of both pressure ratio and acoustic power output is achieved at a critical length for the occurrence of pressure node and velocity antinode in APA, close to but less than one fourth of the wavelength. The distribution characteristics of pressure and velocity in APA are similar to a standing-wave acoustic field, which is the reason for the amplification effect. From the viewpoint of energy, the amplification effect results from the changed distribution of acoustic energy and acoustic power loss in the thermoacoustic system by APA. Experiments have been carried out to validate the simulation, and experimental data are presented.     

Performance of a gas engine driven heat pump for hot water supply systems

The present work aimed at evaluating the experimental performance of a gas engine heat pump for hot water supply. In order to achieve this objective, a test facility was developed and experiments were performed over a wide range of ambient air temperature (10.9-25.3 °C), condenser water inlet temperature (33-49 °C) and at two engine speeds (1300 and 1750 rpm). Performance characteristics of the gas engine heat pump were characterized by water outlet temperatures, total heating capacity and primary energy ratio. The reported results revealed that hot water outlet temperature between 35 and 70 °C can be obtained over the considered range of the operating parameters. Also, total heating capacity and gas engine heat recovery decrease by 9.3 and 27.7%, respectively, while gas engine energy consumption increases by 17.5% when the condenser water inlet temperature changes from 33 to 49 °C. Total heating capacity, gas engine heat recovery and gas engine energy consumption at ambient air temperature of 25.3 °C are higher than those at ambient air temperature of 10.9 °C by about 10.9, 6.3 and 1.5% respectively. Moreover, system primary energy ratio decreases by 15.3% when the engine speed changes from 1300 to 1750 rpm.     

Study on energy flows in thermoacoustic engines utilizing two-temperature heat sources

The proposal of a novel thermoacoustic regenerator using multi-temperature heat sources (MTHS) makes it possible to utilize lower-grade energy and keep relatively high efficiency in a thermoacoustic engine (TE) simultaneously. Based on thermodynamic laws combined with linear thermoacoustic theory, the time-averaged total power, enthalpy flux, acoustic power, entropy flux, and exergy flux in each component are derived and calculated to further understand the mechanism of a TE with the regenerator using two-temperature heat sources (TTHS). The comparison of the energy flows between the traditional TEs and those utilizing TTHS shows that the improvement of the temperature gradient in the regenerator by adding a mid-heater with appropriate heating power can increase the acoustic power and efficiency of a TE.     

Temperatures near the interface between an ideal heat exchanger and a thermal buffer tube or pulse tube

A thermal buffer tube (or pulse tube) thermally isolates two heat exchangers at different temperatures in a thermoacoustic engine or refrigerator while allowing the flow of acoustic power. For many heat transport mechanisms, the quality of the thermal isolation depends on the time-averaged mean temperature distribution in the thermal buffer tube, which is determined by boundary conditions set up by the heat exchangers. However, finite-amplitude effects within one peak-to-peak gas displacement of the heat exchangers can lead to significant modification of the thermal boundary conditions and thus the heat transport. To explore these effects, measured mean temperature profiles in the vicinity of the interface between a heat exchanger and thermal buffer tube are reported for a broad range of acoustic and thermal conditions. A one-dimensional Lagrangian model is developed to predict the mean temperature distribution, and reasonable agreement between experimental data and model results is found for the majority of the acoustic conditions considered.     

Experimental Investigation of Self—sustained Oscillation in a Traveling Wave Thermoacoustic System

A traveling wave thermoacoustic engine consisting of a loop tube with a resonator has been tested. The onset characteristic together with the transition of oscillation mode from traveling wave to standing wave and the periodic shifting between modes in this system are investigated experimentally. The process of self-sustained thermoacoustic oscillation in this heat engine is described and analyzed through phase space distribution reconstructed from the time series of acoustic signal.     

Design and experimental validation of looped-tube thermoacoustic engine

The aim of this paper is to present the design and experimental validation process for a thermoacoustic looped-tube engine. The design procedure consists of numerical modelling of the system using DELTA EC tool, Design Environment for Low-amplitude ThermoAcoustic Energy Conversion, in particular the effects of mean pressure and regenerator configuration on the pressure amplitude and acoustic power generated. This is followed by the construction of a practical engine system equipped with a ceramic regenerator — a substrate used in automotive catalytic converters with fine square channels. The preliminary testing results are obtained and compared with the simulations in detail. The measurement results agree very well on the qualitative level and are reasonably close in the quantitative sense.     

A four power-piston low-temperature differential Stirling engine using simulated solar energy as a heat source

In this paper, the performances of a four power-piston, gamma-configuration, low-temperature differential Stirling engine are presented. The engine is tested with air at atmospheric pressure by using a solar simulator with four different solar intensities as a heat source. Variations in engine torque, shaft power and brake thermal efficiency with engine speed and engine performance at various heat inputs are presented. The Beale number obtained from the testing of the engine is also investigated. The results indicate that at the maximum actual energy input of 1378 W and a heater temperature of 439 K, the engine approximately produces a maximum torque of 2.91 N m, a maximum shaft power of 6.1 W, and a maximum brake thermal efficiency of 0.44% at 20 rpm.