Introduction
Acoustic to electric power conversion
Kees de Blok, Aster Thermoacoustics
Pawel Owczarek, Future energy management-University of Wraclow
Maurice Francois, Hekyom
Brief introduction
Thermoacoustic engine
Multistage traveling wave themoacoustics
High power applications
Acoustic to electric conversion
(movie)
Full scale design
Conclusions
23 juni 2014
1
Introduction
What is thermoacoustics?
•A key enabling energy conversion technology based on "classic"
thermodynamic cycles in which compression, displacement and
expansion of the gas is controlled by an acoustic wave rather then by
pistons and displacers.
•Characteristics
n
n
n
n
n
n
n
n
n
No mechanical moving parts in the thermodynamic process
Maintenance free
Simple construction
Large freedom of implementation
Low noise
High efficiency (>40% of the Carnot factor)
Large temperature range
Scalable from Watt’s to MegaWatt’s
Inert gas like helium, argon or even air as working medium
23 juni 2014
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Introduction
What can we do with thermoacoustics?
Heat supply
at high
temperature
Converting heat into acoustic energy (= mechanical energy)
Þ Heat engine
n
n
n
Heat supply at high temperature from arbitrary heat source
Onset temperature difference » 30ºC
Operating temperature differerence >100ºC
TAEC
Acoustic
output power
Heat sink at a
low
temperature
Converting the acoustic output power into electricity
n Linear alternator (loudspeaker)
n Bi-directional turbine
Heat sink at a
high
temperature
Converting acoustic energy into a temperature lift
(By reversal of the thermodynamic cycle)
Þ Heat pump or refrigerator
n
n
Acoustic
power
Temperature lift: > 80ºC
Temperature range: -200ºC up to 250ºC
TAEC
Heat taken at
low
temperature
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Introduction
Thermoacoustic Heat Engine
Typical operating characteristics
•Low onset and operation temperature
n
No wear and mechanical friction
•Large temperature range
n
No phase change working gas
Thermoacoustic cooler
23 juni 2014
Thermoacoustic heat pump
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Thermoacoustic engine
Basic geometry of a thermoacoustic
engine
n
Above onset temperature acoustic
power gain exceeds losses and
oscillation start
n
Oscilllation frequency is set by
(acoustic) length of the feedback tube
n
At increasing input temperature (above
onset) part of the acoustic loop power
can be extracted as net output power
Acoustic output power can be converted to
n
electricity …
n
or drive a termoacoustic heat pump
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Multi-stage traveling wave thermoacoustics
Utilizing low and medium temperature heat sources
•Waste heat
•Solar (vacuum tube collectors)
•Geothermal
•…….
•.
Multi stage traveling wave thermoacoustic engine
n
Increase of acoustic power gain proportional with
4-stage thermoacoustic traveling wave engine (THATEA project)
number of stages
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Less acoustic loop power relative to the net acoustic
output power (more compact design)
n
Oscillation frequency set by the acoustic length
n
Onset temperature difference < 30°C
n
Operating temperature difference > 100 °C
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High power applications
100 kW T Thermo Acoustic Power generator
Thermoacoustic power (TAP)
Conversion of industrial waste heat
into electricity
•SBIR project phase2
nDesign and built of a TAP converting
100 kW waste heat at 160ºC into 10
kW electricity
nLocation: Smurfit Kappa Solid Board,
Nieuweschans(Gr)
Other (industrial) applications
•Heat transformer
3m
nUpgrade waste heat above the pinch
•Gas liquefaction
nStorage and transport of LNG
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High power applications
Conclusions of the TAP project in 2011
•Thermoacoustic energy conversion itself can be scaled up
in power succesfully
•Upscaling toward high power applications is blocked by the
linear alternators
Practical issues
n Piston stroke limited by stroke of the springs
n Size and weigth of moving mass more than proportional with power
(Larger TA system Þ lower frequency Þ less induction)
n Sensitive for overload
n Vibration
Economic issues
n Cost > 3000 € / kW
n No mass production
n Per kW electrictricity relativelly large amont of magnetic materiaal
n Availability and cost of raw materials for strong magnets (neodynium)
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The TAP Linear alternator
Acoustic to electric conversion
Acoustic wave motion
1) Using the acoustic wave pressure component
Convert periodic pressure variation into periodic
bi-directional linear motion (piston, membrane)
Pressure
amplitude
Mean
pressure
n Linear alternators
n MHD
n Piezo electric effect
2) Using the acoustic wave velocity component
0
0
Convert periodic bi-directional velocity into unidirectional rotation
n Bi-directional turbine
Gas
displacement
amplitude
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Acoustic to electric conversion
Bi-directional turbines
Guide vanes
Guide vanes
Rotation is independent of flow direction
Rotor
Know embodiments
•Lift based turbines
Wells turbine
Darrieus rotor (wind turbine)
•Impulse based turbines
Savonious rotor (ventilation)
Axial impulse turbine
Radial impulse turbine
Existing technology used for oscillating
water column (OWC) wave power plants
(30-500kWe)
Bron: Limpet 500
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Acoustic to electric conversion
Axiale impuls turbine
Acoustic experiments on scale models
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Radial impuls turbine (100mmÆ)
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Axial impuls turbine (72mmÆ)
Both manufactured in SLA-SMS 3-D printing.
brushless DC elektromotor used as generator
Observations:
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Radial turbine
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Relation rotor efficency and frequency
Higher torque at lower rotational speed
Axiale turbine
n
Lower torque at higher rotational speed
•
Better efficiency for AC flow
•
Output power and efficiency observed to be
hardly dependent of acoustic frequency
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Acoustic to electric conversion
Scaling experiment at the 100 kW TAP SKSB
Radiale impuls turbine voor de TAP (Drotor =300 mm)
Linear alternator replaced by radial bi-directional inpulse
turbine
•Measured rotor efficiency of 75% at 0.8MPa
•Efficiency proportional with fluid density
Radiale impuls turbine in position in engine stage #2
23 juni 2014
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Acoustic to electric conversion
Test axial turbines in the 100kW TAP
Turbine in preparaton
Manufactured by AGAN italy
Axial turbine :
Rotor diameter: 200mm
Rotational speed : 2700rpm
Power: 2 kW
Generator : Outer runner permanent magnet motor
Turbine position inside the TAP
Aim of this experiment
•Validate turbine model
•Acoustic impedance
•Avoid radial induced streaming
•Confirm feasible turbine effciency
•Starting point for manufacturing and turbine optimization
Efficiency in air at 0.8MPa of this axial bi-directional
turbine is measured to be 80%
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Full scale design 1MW T
•
Basic thermoacoustic engine stage
High temperature
heat exchanger
Regenerator
Low temperature
heat exchanger
Bi-directional
turbine +
generator
Acoustic
power out
Low temperature
cooling circuit
15-40°C
(Waste) heat in
(140-250°C)
Acoustic
power in
Electricity out
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Full scale design 1MW T
Looped heat-pipe
circuits
Flue gas heat
exchanger
2m
Roof section or
mounting platform
Heat sink terminals
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Conclusions
•The TAP concept is theroretical and experimentally validated and recognized as a compatitive
technology for converting waste heat into electricity.
•Upscaling in power toward industrial levels however was blocked by the increasing cost, mass and
complexity of linear alternators
•As a practical and economic viable alternative for linear alternators at increasing power levels the
concept of a bi-directional turbine, converting acoustic power into rotation and from there into electricity,
is introduced and tested succesfully
•Rotor efficiency defined as shaft output power over acoustic input power is a function of fluid density,
and is measured to raise from about 30% at atmospheric pressure up to 80% for air at 0.8MPa.
•As a major achievement, the initial limitation in upscaling the thermal and electric power levels is
abrogated, paving the way for full scale application of thermoacoustic waste heat recovery in industry up
to MW scale
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