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8/13/2019 Multistage thermoacoustic engine by Subhan Ullah
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MULTI-STAGE TRAVELING WAVE
THERMOACOUSTICS
IN PRACTICE(Kees de Blok, 19th International Congress on Sound and
Vibration, Vilnius, Lithuania, July 8-12, 2012)
Student: Subhan Ullah
Advisor: Prof. Akiyoshi Iida
Assistant Prof. Hiroshi Yokoyama
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Table of contents
Introduction Background
Previous research
Objective
MethodologyMain components of TA-engine
Acoustic resonators
Regenerators
Heat exchangers
Results
Conclusions
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Introduction
Background
Previous research
Objective
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Simple TA-engine(Prime mover) and
TA-Refrigerator(Heat pump)
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Multi-stage TA-engine
Red = Heat in at Thigh
Blue = Heat out at Tlow
Green = Acoustic loop power
In this case the mutual distance between
the regenerator units is L
There are four loads attached
with each stage
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Cont
An option to increase thermoacoustic power gain at medium
and low operating temperatures is to use multiple
thermoacoustic units or cores, changing the size of
regenerators, or adding an acoustic load per stage
A special configuration suggested by de Blok is, when an even
number (typically two or four) of equally spaced regenerators
is inserted inside the feedback loop, so that the distance fromone regenerator to the other is half of the wave length in the
case of a two-stages engine, and a quarter of the wavelength
in the case of a four-stages engine
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Thermoacoustic power (TAP)
TAP was designed for converting 100 kW of thermal power of
flue gas at 150-160C into 10 kW electricity with an exegetic
efficiency of > 40%.
Basically it is also a 4-stage traveling wave feedback system
using helium at a mean pressure of 750 kPa as working gas
The 1.64 kW output power is reached with helium at a meanpressure of 750 kPa and at only 1.7% drive ratio.
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Previous research
1777, Dr. Bryan Higgins
In 1859, Rijke (open ends, air, and 1/4L)
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Cont
Sondhauss in 1850 (earliest known predecessor to todays
standing wave thermoacoustic engines )
Can work horizontally
No ascending air current is required for oscillations
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Cont
Carter in 1962, introduced a stack of parallel plates inside the
tube which made it easier to exchange heat with the working
gas
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Cont
In 1979, Peter H. Ceperley:
Toroidal geometry
acoustic Stirling engine
The high and low temperature heat exchangers and the stack
or regenerator altogether are sometimes referred to as astage.
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Thermoacoustic power (TAP)
TAP was designed for converting 100 kW of thermal power of
flue gas at 150-160C into 10 kW electricity with an exegetic
efficiency of > 40%. Basically it is also a 4-stage traveling wave
feedback system using helium at a mean pressure of 750 kPa
as working gas
At an input of 99 C and heat rejection at 20 C this
corresponds with 38% effeciency.
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Objectives
Emphasis in this document is on acoustic loss in the acoustic
resonance and feedback circuitry which has turned out to be
the major issue in the design of useful integral
thermoacoustic systems.
To test an integral system of a low temperature
thermoacoustic engine driving a thermoacoustic refrigerator.
Practical reasonable application of Thermoacoustics.
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Methodology
Main components of TA-engine
Acoustic resonators:
A: Standing-wave resonators
B: Helmholtz type resonators
C: Acousto-mechanical resonators
D: Traveling wave or loop resonators
Regenerators
Heat exchangers
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Cont
C: the Acousto-mechanical resonator The mass is acting like a resonator.
D: The traveling wave feedback loop
The load is connected to the acoustic source by one wavelength long feedback tube.
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Regenerator
Sample of the material for the ceramic regenerator: general view (left); close
up of the channel structure(right)
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Heat exchangers
There are two types of heat exchangers
Hot (left) and cold (right) heat exchanger assemblies
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Results
Ranking of resonator tubes
Coupling efficiency = P(Acoustic load) / P(Acoustic source)
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There are less losses in mechanical resonator
but in practice it is difficult to make it.
The travelling wave resonator has the lowest
loss and also it is more compact.
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Table 1: Performance of the integrated system measured at increasing engine
input temperature
ENGINE
TH_EHot hex inputtemperature C 169 211 239
TC_ECold hex inputtemperature C 12 13.2 13
QE Thermal input power W 1041 1300 1728
Qstat Static heat loss W 235 296 340
TH_regRegenerator high
temperature C 138 178 199
TC_regRegenerator low
temperature C 32.1 38.8 47
Pac1Acoustic power at
refrigerator input (#1) 134 192 274
Pac2Acoustic power atengine input (#2) W 73.0 91.4 121
WfbAcoustic loss
feedback W 21.4 30.8 44
Wout_E
Acoustic output
power (Pac1Pac2+
.Wfb) W 76.6 124 187
T_E
Thermal efficiency
(Wout_E/ QE) - 0.10 0.14 0.15
2_E
Exegetic efficiency
relative to TH_E - 0.29 0.34 0.35
2_E_reg
Exegetic efficiency
relative to TH_reg - 0.42 0.48 0.5011/10/2013 22
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Table 2 shows the results for three engine input temperatures
and the lowest cold hex temperature obtained after the system
becomes thermally stable
REFRIGERATOR
dr Drive ratio at cold hex % 1.33 1.53 1.78
Win_R
Acoustic input power
(Pac1
Pac2
.Wfb) W 55.2 93.4 143
Tc_R Cold hex temperature C -33.7 -40.5 -45.5
QC_R Net cooling power W 78.2 95.1 95.4
TH_RAfter refrigerator
temperature C 19.2 24.2 18.8
QH_R Heat rejected W 135 182 253
COP ( QC_R/ Win_R) - 1.42 1.02 0.67
2_R
Exegetic efficiency
relative to TC_R - 0.32 0.29 0.19
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The performance of the engine is strongly affected by the
temperature drop across the heat exchangers.
In this paper only the overall integral system results are
presented.
The working gas is helium at 2.7 Mpa and frequency is 95 Hz.
Performance of the integral system is measured at three
different engine input temperatures.
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