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Journal ArticleDOI

Acoustic matching of a traveling-wave thermoacoustic electric generator

05 Jun 2016-Applied Thermal Engineering (Pergamon)-Vol. 102, pp 272-282

AbstractAcoustic 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 750.4 W 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 506.4 W 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.

Topics: Thermoacoustics (61%), Acoustic impedance (61%), Linear alternator (59%), Alternator (automotive) (55%), Electric generator (54%)

Summary (4 min read)

1. Introduction

  • Traveling-wave thermoacoustic electric generator is capable of converting thermal energy into electric power with high reliability and efficiency with very simple structures.
  • After further optimizations, the system was able to achieve 473.6 W electric power and 14.5% thermal-to-electric efficiency [17].
  • Therefore, the match of the acoustic impedances between the thermoacoustic engine and the linear alternator is critical to the overall performance.
  • The effects of the acoustic impedance on the performance of the thermoacoustic system and whether the systems were acoustically well matched have not been studied by the above work.

2. Procedure of acoustic impedance match

  • Acoustic impedance denotes the ratio of pressure to volume flow rate in acoustic systems, such as thermoacoustic engines, pulse tube refrigerators, etc. Acoustic impedance Za is defined by, UpUpaaa U p j U p U p ZjZZ sincosImRe 1 1 1 1 1 1 (1) where, 1p and 1U denote the complex pressure amplitude and volume flow rate amplitude, respectively;.
  • Up is the phase difference between the pressure and volume flow rate.
  • When the acoustic impedance is matched in a thermoacoustic electric generator, it means that the thermoacoustic engine and the linear alternators can both work at or near their optimal working conditions simultaneously when they are connected.
  • Secondly, the required acoustic impedances to reach the optimal performances of the engine and the alternators should be matched.
  • In electrics, an effective way of realizing the electric impedance match in a power circuit is to introduce the concepts of input impedance of the electric load and the output impedance of the electric source, and design the load and electric source separately.

3. Experimental Setup

  • Figure 2 illustrates the schematic of the traveling-wave thermoacoustic engine [17].
  • The regenerator (REG) is the key component where thermoacoustic energy conversion happens, and is filled with stainless steel screens with a mesh number of 120.
  • The main ambient heat exchanger (MAHX) is of shell-tube type with working gas oscillating inside the stainless steel tubes with inner diameters of 2 mm and the chilling water flowing through the shell sides.
  • The schematic of the linear alternators, which are supplied by Lihan Thermoacoustic Technologies Co. Ltd, are depicted in Figure 3.
  • The generated electric power is therefore dissipated by the load resistance.

4. Output acoustic impedance of thermoacoustic engine

  • Requirements of acoustic impedances for coupling the engine and the load are different at different output positions.
  • Therefore, the output acoustic impedance characteristics can be simply modulated by changing the location for connecting the load.
  • A numerical model of the traveling-wave thermoacoustic engine is first built based on DeltaEC (Design Environment for Low-amplitude ThermoAcoustic Energy Conversion) [31].
  • The output acoustic power, thermoacoustic efficiency, pressure amplitude, volume flow rate, and frequency at different acoustic impedances can then be calculated by setting different values of the real and imaginary parts of the BRANCH component.
  • In the calculations, the hot and ambient heat exchangers are set at 650 °C and 13 °C, respectively.

4.1 Operating frequency

  • Figure 4 shows the variation of operating frequency of the thermoacoustic engine with the output impedance at the two output locations.
  • It is shown that the output acoustic impedance has weak effects on the operating frequency, especially at relatively high acoustic impedances.
  • In general, the operating frequencies of the engine are around 65.5 Hz.

4.2.1 Location A

  • Variations of the output acoustic power and thermoacoustic efficiency of the thermoacoustic engine with the acoustic impedance at location A are given in Figure 5(a) and Figure 6(a), respectively.
  • It is both beneficial for the power and the efficiency if the imaginary part Im[Za] of the output acoustic impedance approaches zero, which means the acoustic load is a pure acoustic resistance.
  • Increasing the magnitude of Im[Za] results in a decrease of the maximum output acoustic power and the thermoacoustic efficiency, especially the latter one.
  • The required output acoustic impedances of the engine for the maximum output acoustic power and thermoacoustic efficiency are not the same, and a compromise should be made when modulating the acoustic impedance of the load.

4.2.2 Location B

  • Variations of the output acoustic power and thermoacoustic efficiency of thermoacoustic engine with the acoustic impedance at location B are given in Figure 5(b) and Figure 6(b), respectively.
  • Similar to the trends with location A, both the output acoustic power and thermoacoustic efficiency are able to reach the higher maximum values when the imaginary part of the output acoustic impedance approaches zero.
  • When the imaginary output acoustic impedance Im[Za] is zero, the maximum output acoustic power of 837 W and highest thermoacoustic efficiency of 0.31 are achieved at the real output acoustic impedances Re[Za] of 1.8×107 Pa·s/m3 and 9×106 Pa·s/m3, respectively.
  • The ranges to achieve the relatively high acoustic power and efficiency are enlarged, which makes it easier for adjusting the acoustic impedance of the linear alternator to fall into the sweet spot range.
  • When Im[Za] is far away from zero, for example at the scale of 10 7 Pa·s/m3, the performances of the thermoacoustic engine are largely degraded.

4.3 Equivalent displacement

  • During the modulation of the acoustic impedance, the output acoustic power may exceed the maximum value that can be extracted by the linear alternators, and make the linear alternator be overloaded in displacements.
  • The volume flow rate |U1| at the output position is converted into the equivalent displacement |x1| of the linear alternators by using the relationship of |x1|=0.5|U1|/ωA.
  • Recalling the output performances given in Figure 5 and 6, though relatively good performances can still be obtained at these impedances, it is not appropriate to couple the linear alternators with the engine at these acoustic impedance ranges due to the overloaded displacements.

5.1 Effect of operating frequency

  • Figure 8 shows the dependences of input acoustic power and output electric power on operating frequency for one linear alternator at fixed pressure amplitude and load resistance.
  • The variations of the acoustic impedances of the linear alternator with the operating frequency are shown in Figure 9.
  • The imaginary part of the acoustic impedance reaches zero at the resonant frequency.
  • This is why the acoustic power extracted and the electric power generated at the resonant frequency reach the maximums.
  • When the operating frequency is far away from the resonant one, the acoustic power that can be extracted by the linear alternator is largely decreased due to the large acoustic reactance.

5.2 Effect of electric capacitance

  • Figure 10 and Figure 11 shows the effects of the connected electric capacitance on the input acoustic impedance and acoustoelectric efficiency of the two linear alternators when the load resistance is at 100 Ω and 180 Ω, respectively.
  • The above analysis shows that the linear alternators cannot be matched to the thermoacoustic engine at either location A or location B when the electric capacitance is either larger than 100 μF or smaller than 1 μF.
  • It denotes that the system is acoustically matched and the optimal performance can be obtained at the location B.

5.3 Effect of load resistance

  • Figure 12 and Figure 13 show the effects of the load resistance on the input acoustic impedance and acoustoelectric efficiency of the linear alternators when the electric capacitance is 9.6 μF, which is consistent with that used in the following experiments.
  • As shown in Figure 12, when no electric capacitance is connected in the circuit, both the real and imaginary parts of the acoustic impedance have very limited variation ranges when adjusting the load resistance.
  • It indicates that the load resistance has great effects on the real and imaginary parts of the input acoustic impedance of the linear alternator, which makes it possible to modulate the acoustic impedance in a large enough range to match with the thermoacoustic engine.
  • As shown in Figure 13, the acoustoelectric efficiency of the linear alternators first increases and then has a slightly decrease when increasing the load resistance.
  • The efficiency with the electric capacitance is higher than that without an electric capacitance at any load resistance, showing the importance of the electric capacitance.

6.1 Matching of operating frequency

  • The operating frequency is adjusted by using two different working gas, i.e. helium and nitrogen gases in the experiments.
  • When nitrogen is used as working fluid, the operating frequency of the whole system is about 23 Hz, which is much lower than the mechanical resonant frequency of the linear alternator.
  • It shows that both the electric power and the efficiency of the system with helium as the working fluid are much higher than those with nitrogen.
  • The optimal output acoustic power of the engine with nitrogen is about 260 W.
  • The results show that the match of the operating frequency is critical to the impedance match of the thermoacoustic electric generator.

6.2 Coupled at location A

  • Based on the above analysis about the match of the operating frequency, helium is used as the working fluid in the following experiments.
  • Figure 15 and Figure 16 shows the frequency, pressure amplitude, displacement, and electric current of the thermoacoustic electric generator when the engine and the alternator are coupled at location A.
  • All the four calculated parameters have good agreements with the experimental ones, showing the good accuracy of the numerical model.
  • The maximum electric power reaches 506.4 W in the experiments.
  • Tests are not conducted below 60 Ω for the safety concerns.

6.3 Coupled at location B

  • According to the output acoustic impedance of the thermoacoustic engine and the input acoustic impedance of the linear alternators, the engine and the alternators can be better matched at location B by adjusting the electric capacitance and the load resistance to be 9.6 μF and 100 Ω, respectively.
  • Therefore, the displacement increases when increasing the load resistance due to the reduced real acoustic impedance.
  • Figure 20 shows the relationship of output electric power of the coupled system with the real part of the acoustic impedance of the linear alternators.
  • When the heating temperature is fixed at 650 °C, the electric power reaches its maximums of 765.8 W in the simulations and 750.4.
  • The trends of the numerical results are similar to the experimental ones.

7. Conclusions

  • The general procedure for the impedance match is proposed systematically.
  • Two different coupling positions, including location A at the feedback loop and location B at the resonator, are investigated to modulate the output acoustic impedances of the engine.
  • This work was supported by National Natural Science Foundation of China under contract No. 51476136 and China Postdoctoral Science Foundation under contract No. 2013M541772.

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1
Acoustic matching of a traveling-wave thermoacoustic electric generator
Kai Wang
a,b,c
, Jie Zhang
a,b
, Ning Zhang
a,b
, Daming Sun
a,b *
, Kai Luo
a,b
, Jiang Zou
a,b
, Limin Qiu
a,b
a
Institute of Refrigeration and Cryogenics, Zhejiang University, Hangzhou 310027, PR China
b
Key Laboratory of Refrigeration and Cryogenic Technology of Zhejiang University
c
Energy Research Institute @ NTU, Nanyang Technological University, Singapore 637141
Abstract
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 750.4 W
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 506.4 W 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.
Keywords: thermoacoustic; linear alternator; acoustic impedance; impedance match
*
Corresponding author. Tel/Fax: +86-571-87952769 (Daming Sun)
E-mail address: wangkai7089@gmail.com (Kai Wang), sundaming@zju.edu.cn (Daming Sun)

2
1. Introduction
Traveling-wave thermoacoustic electric generator is capable of converting thermal energy into
electric power with high reliability and efficiency with very simple structures. It is typically
composed of a traveling-wave thermoacoustic engine [1-7] or several traveling-wave
thermoacoustic conversion units [8, 9] that consist of a hot heat exchanger, a regenerator and a cold
heat exchanger, and several linear alternators. The externally added thermal energy is first converted
into acoustic energy by the thermoacoustic engine, and then into electric power by the linear
alternators.
In recent ten years, many research groups have been devoted into the developments of the
thermoacoustic electric generation system, and great progress has been made. The earliest
thermoacoustic electric generator was built by Backhaus et al. [10] in 2004, which achieved an
electric power of tens of watts. The long resonator in a traditional traveling-wave thermoacoustic
engine is firstly completely replaced by the linear alternators in the system. Sunpower, Inc. later
developed a similar traveling-wave thermoacoustic electric generator with an output power of about
50 W [11]. Wang et al. experimentally optimized the shapes of the phase adjusting components at
the coupling port of a small traveling-wave thermoacoustic electric generator and achieved about 73
W electric power [12]. Luo et al. [9, 13-15] have conducted a series of research work on
traveling-wave thermoacoustic electric generators. They proposed a double-acting thermoacoustic
electric generator removing the long gas resonator, which is composed of three sets of
thermoacoustic conversion units and three linear alternators arranged in a loop [15]. The designed 3
kW-scale system achieved the maximum electric power of 1.57 kW with an efficiency of 16.8%.
Later, a three-stage resonant thermoacoustic electric generator capable of generating about 5 kW
electric power was developed [9]. Sun et al. [16, 17] were also engaged into the developments of
traveling-wave thermoacoustic electric generators recently. The effects of the mechanical and
electric resonances on the performances of a traveling-wave thermoacoustic electric generator with
a resonator were investigated [16]. An electric power of 345.3 W and a thermal-to-electric
efficiency of 12.33% were achieved. After further optimizations, the system was able to achieve
473.6 W electric power and 14.5% thermal-to-electric efficiency [17]. Several other research groups
adopted low-cost loudspeakers as the electric convertors in traveling-wave thermoacoustic electric
generators [18-21]. The achieved electric powers ranged from several watts to about 200 W and the
thermal-to-electric efficiencies were typically less than 5%.
In a traveling-wave thermoacoustic engine, the linear alternators act as the acoustic load to the
thermoacoustic engine. The acoustic impedance of the linear alternators has great effects on the
performances of the engine. Besides, the required acoustic impedance for coupling the
thermoacoustic engine also affects the acoustic-to-electric conversion of the linear alternators.
Therefore, the match of the acoustic impedances between the thermoacoustic engine and the linear
alternator is critical to the overall performance. In some cases, the system is even not able to work if
they don’t match.

3
Swift [22] pointed out that the best position for placing an acoustoelectric transducer in a
standing-wave resonator depends on the acoustic impedance of the transducer itself.
High-impedance transducer should be placed at a point of high acoustic impedances, and a
low-impedance transducer is best located at a point of low acoustic impedances. This is one of the
earliest statements about the impedance match in a thermoacoustic system. Several researchers
[23-27] used the equivalent circuit method to obtain the equivalent acoustic impedances of the
acoustoelectric transducers, and then coupled it with standing-wave thermoacoustic systems. The
effects of the frequency on the efficiencies of the transducers were extensively studied. However,
the effects of the acoustic impedance on the performance of the thermoacoustic system and whether
the systems were acoustically well matched have not been studied by the above work. Dai et al. [28]
studied the impedance match for Stirling type cryocoolers. The study mainly focused on the
requirements of the acoustic impedance for maximizing the efficiency and output acoustic power of
the linear compressors, while the characteristics of the cryocooler part were not considered. Hatori
et al. [29] reported an experimental method to determine the acoustic impedances of a
traveling-wave thermoacoustic loop and its acoustic load by using an acoustic driver. Sun et al. [5]
studied the output characteristics of a traveling-wave thermoacoustic engine, and showed that the
output position have great effects on the output performances. It was demonstrated that the double
output method helped to improve the output performances. Zhang et al. [30] studied the output
characteristics of a traveling-wave thermoacoustic engine numerically and experimentally. RC-type
and RL-type acoustic loads driven by the engine were studied and compared. It was shown that the
acoustic impedance is critical and unique for a good output performance. The work is helpful for
designing an appropriate acoustic load to couple with the engine. In the studies about the small
thermoacoustic electric generator, Backhaus et al. [10] pointed out that the moving mass of the
linear alternators should be in a resonance state under the combined actions of the forces from the
gas spring, the flexure bearing and the electromagnetism effect. The details about the designs and
impedance match were not presented. In the work about the kW-class thermoacoustic electric
generator of Ref. [14], the system was not operated at its optimal acoustic impedance when pure
helium is used as the working gas due to the mismatch of the working frequency. Argon-helium
mixed gas was used to decrease the frequency so as to have a better impedance match. In all, there
are few detailed and comprehensive studies about the impedance match between the thermoacoustic
engine and the alternators in thermoacoustic electric generation systems. Particularly, the effects of
the coupling positions of the linear alternators on the performance of the thermoacoustic electric
generation systems have never been studied. How to match the system effectively by modulating
the acoustic impedances of the engine and the linear alternators to achieve the best performance still
remains a question.
In this paper, the acoustic impedance match in a traveling-wave thermoacoustic electric
generator is studied numerically and experimentally. The general procedure to match the
thermoacoustic engine and the linear alternators to reach an acoustically well matched working
condition is presented. The acoustic impedance characteristics of the thermoacoustic engine and the

4
linear alternators are then calculated and analyzed individually. Two different locations for coupling
the linear alternators are investigated and compared. Several effective measures are used to match
the acoustic impedances. Experiments are finally conducted to verify the numerical analysis and
demonstrate the acoustically well matched working conditions.
2. Procedure of acoustic impedance match
Acoustic impedance denotes the ratio of pressure to volume flow rate in acoustic systems, such
as thermoacoustic engines, pulse tube refrigerators, etc. Acoustic impedance Z
a
is defined by,
UpUpaaa
U
p
j
U
p
U
p
ZjZZ
sincosImRe
1
1
1
1
1
1
(1)
where,
1
p
and
1
U
denote the complex pressure amplitude and volume flow rate amplitude,
respectively;
Up
is the phase difference between the pressure and volume flow rate.
A traveling-wave thermoacoustic electric generator is generally composed of a traveling-wave
thermoacoustic engine and several linear alternators. When the acoustic impedance is matched in a
thermoacoustic electric generator, it means that the thermoacoustic engine and the linear alternators
can both work at or near their optimal working conditions simultaneously when they are connected.
The coupled system is able to achieve the maximum electric power output and the highest
thermal-to-electric efficiency at its full potential. In order to achieve the matching condition stated
above, three aspects of matching should be considered. Firstly, the frequencies of the engine and the
alternators should be matched so that the coupled system is harmonically operated. Secondly, the
required acoustic impedances to reach the optimal performances of the engine and the alternators
should be matched. In other words, they can be both operated at the optimal states simultaneously at
a certain acoustic impedance and frequency. Thirdly, the output acoustic power of the engine and
the acoustic power that can be extracted by the alternators should be matched.
In previous studies on thermoacoustic systems, it was a regular approach to first build a
complete model of the whole system, and then investigate the effects of different parameters on the
system performances so as to find the direction for optimization. It is worth noting that the
thermoacoustic engine and the linear alternators not only work synergistically as a coupled system,
but also work independently in a thermoacoustic electric generator. If the aforementioned approach
is used in such a strongly coupled system, the critical information about the optimal working
conditions that the engine and the alternators require may be covered. It is difficult to know whether
the sub-systems have reached their optimal working conditions if only the whole model is
investigated. Besides, due to so many adjustable parameters in the whole system, it is also a
challenge to find the clear direction for the optimization and realize the acoustic match between the
engine and the alternators.
In electrics, an effective way of realizing the electric impedance match in a power circuit is to
introduce the concepts of input impedance of the electric load and the output impedance of the

5
electric source, and design the load and electric source separately. When the input and output
impedances are adjusted to be the same, the electric load and the source can be matched to form a
more complex electric circuit. Inspired by the idea, we propose to realize the acoustic impedance
match of the thermoacoustic electric generator in the procedure illustrated in Figure 1. The
characteristics of the required acoustic impedances for the operations of the engine and alternators
are first analyzed independently. According to the requirements of the acoustic impedances, their
acoustic impedances are then adjusted to be the same when they can operate at or near their optimal
states simultaneously. Finally, the engine and the alternators are coupled at the modulated acoustic
impedance.
Analyze the output acoustic impedance of
thermoacoustic engine
Analyze the input acoustic impedance of
linear alternators
Modulate the output and input
acoustic impedances
Couple the whole system
Matched?
Acoustically matched
thermoacoustic electric generator
No
Yes
Figure 1. Procedure of impedance matching of thermoacoustic electric generator.
3. Experimental Setup
Figure 2 illustrates the schematic of the traveling-wave thermoacoustic engine [17]. It mainly
consists of a regenerator, several heat exchangers, a feedback loop and a gas resonator. The
regenerator (REG) is the key component where thermoacoustic energy conversion happens, and is
filled with stainless steel screens with a mesh number of 120. The copper heat transfer element
inside the hot heat exchanger (HHX) is of fin type with a fin thickness of 0.5 mm and a gap of 1
mm. The main ambient heat exchanger (MAHX) is of shell-tube type with working gas oscillating
inside the stainless steel tubes with inner diameters of 2 mm and the chilling water flowing through
the shell sides. The total number of the thin tubes is 301. The second ambient heat exchanger
(2AHX) is also of the shell-tube type composed of 199 tubes with an inner diameter of 3 mm. In the
experiments, the temperatures of the HHX and the AHXs are kept at 650 °C and 13 °C, respectively.
The detailed dimensions of the traveling-wave thermoacoustic engine are listed in Table 1. Two

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Cites background from "Acoustic matching of a traveling-wa..."

  • ...49 Many efforts were recently devoted into employing the engine for power generation by using linear alternators 50 [19-25]....

    [...]

  • ...It indicates that the middle coupling position is a low acoustic impedance region, which also requires 190 a low load acoustic impedance for better output performances [19]....

    [...]

  • ...Previous work on thermoacoustic-linear alternator coupled systems 72 showed that the acoustic matching between them is critical for the overall performance [19]....

    [...]


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References
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Proceedings Article
W. P. Arnott1, R. Raspet1, H.E. Bass1
01 Jan 1991
Abstract: Thermoacoustic engines (TAEs) can be used to pump heat using a sound wave or pump a sound wave using a temperature gradient. The basic arrangement is a gas-filled acoustic resonator with appropriately positioned thermoacoustic elements. Two types of thermoacoustic elements are used in these engines: (1) heat exchangers used to communicate heat between the gas and external heat reservoirs; and (2) the TAE, also known as a stack. The TAEs are sections of porous media that support the temperature gradient, transport heat on the acoustic wave between the exchangers, and produce or absorb acoustic power. Previous results have been developed for TAEs with circular or parallel slit pore geometries. The theory is extended for gas-filled TAEs to include pores of arbitrary cross-sectional geometry. An approximate analysis of energy flow and acoustical measurements of a thermoacoustic prime mover are given. >

774 citations


"Acoustic matching of a traveling-wa..." refers background in this paper

  • ...596 [22] G.W. Swift, Thermoacoustic engines, The Journal of the Acoustical Society of America, 84 (1988) 597 1145-1180....

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  • ...69 Swift [22] pointed out that the best position for placing an acoustoelectric transducer in a 70 standing-wave resonator depends on the acoustic impedance of the transducer itself....

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  • ...615 [31] B. Ward, J. Clark, G.W. Swift, Design Environment for Low-amplitude Thermoacoustic Energy Conversion....

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Journal ArticleDOI
Abstract: Traveling-wave thermoacoustic heat engines have been demonstrated to convert high-temperature heat to acoustic power with high efficiency without using moving parts Electrodynamic linear alternators and compressors have demonstrated high acoustic-to-electric transduction efficiency as well as long maintenance-free lifetimes By optimizing a small-scale traveling-wave thermoacoustic engine for use with an electrodynamic linear alternator, we have created a traveling-wave thermoacoustic electric generator; a power conversion system suitable for demanding applications such as electricity generation aboard spacecraft

175 citations


"Acoustic matching of a traveling-wa..." refers background in this paper

  • ...93 [10] pointed out that the moving mass of the linear alternators should be in a resonance state 94 under the combined actions of the forces from the gas spring, the flexure bearing and the 95...

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  • ...[10] in 2004, which achieved 40 an electric power of tens of watts....

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Journal ArticleDOI
Abstract: The Los Alamos thermoacoustics code, available at www.lanl.gov/thermoacoustics/, has undergone extensive revision this year. New calculation features have been added to the original Fortran computational core, and a Python‐based graphical user interface wrapped around that core provides improved usability. A plotter routinely displays thermoacoustic wave properties as a function of x or tracks results when a user‐specified input variable, such as frequency or amplitude, is varied. The Windows‐like user interface provides mouse‐based control, scrolling, and simultaneous displays of plots and of several categories of numerical values, in which color indicates important features. Thermoacoustic phenomena can be calculated with superimposed steady flow, and time‐averaged pressure gradients are calculated. In thermoacoustic systems with toroidal topology, this allows modeling of steady flow caused by gas diodes (with or without time‐averaged heat transfer) and Gedeon streaming. Thermoacoustic mixture separation is included, also with superimposed steady flow. The volume integral of the complex gas momentum is available, so vibrations of thermoacoustic systems can be analyzed.

168 citations


"Acoustic matching of a traveling-wa..." refers methods in this paper

  • ...197 A numerical model of the traveling-wave thermoacoustic engine is first built based on 198 DeltaEC (Design Environment for Low-amplitude ThermoAcoustic Energy Conversion) [31]....

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Journal ArticleDOI
Abstract: This paper proposes a novel concept of a travelling-wave thermoacoustic electricity generator, which employs a looped-tube travelling-wave thermoacoustic engine to convert thermal energy into acoustic power, an ultra-compliant alternator within the engine loop to extract and convert the engine acoustic power to electricity and an acoustic stub matching technique to match the alternator to the engine. In addition, a carefully designed cold heat exchanger acts as a phase shifting inertance to improve the performance. A simple model has been developed to capture and demonstrate the physics of this new concept, while the whole system has been investigated in detail numerically by using a specialized design tool DeltaEC. Based on the current concept, a prototype has been designed, constructed and tested. It uses atmospheric air as the working fluid, a commercially available audio loudspeaker as the electro-dynamic transducer, and inexpensive standard parts as the acoustic resonator. The experimental results have verified the simplified model and the numerical simulations of the practical build. The small-scale inexpensive prototype generator produced 11.6 W of electrical power, which shows the potential for developing cheap thermoacoustic electricity generators for energy recovery from waste heat sources. It is concluded that such concept could be very attractive provided that inexpensive ultra-compliant alternators based on the standard technology used in audio loudspeakers could be developed. Finally, some guidelines have been discussed and proposed for developing such alternators.

134 citations


"Acoustic matching of a traveling-wa..." refers background in this paper

  • ...Several other research groups adopted low-cost loudspeakers as the electric convertors 59 in traveling-wave thermoacoustic electric generators [18-21]....

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Journal ArticleDOI
Tianjiao Bi1, Zhanghua Wu1, Limin Zhang1, Guoyao Yu1, Ercang Luo1, Wei Dai1 
Abstract: 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 4.69 kW with thermal-to-electric efficiency of 15.6% and the maximum thermal-to-electric efficiency of 18.4% with electric power of 3.46 kW were achieved with 6 MPa 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.

75 citations


"Acoustic matching of a traveling-wa..." refers background in this paper

  • ...4 resonant thermoacoustic electric generator capable of generating about 5 kW electric power 52 was developed [9]....

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  • ...[9, 13-15] have 46 conducted a series of research work on traveling-wave thermoacoustic electric generators....

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  • ...It 32 is typically composed of a traveling-wave thermoacoustic engine [1-7] or several 33 traveling-wave thermoacoustic conversion units [8, 9] that consist of a hot heat exchanger, a 34 regenerator and a cold heat exchanger, and several linear alternators....

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