Upload
others
View
2
Download
0
Embed Size (px)
Citation preview
30 oktober 2015 1
Introduction
Beyond acoustic to electric power conversion limits
Kees de BlokAster Thermoacoustics
www.aster-thermoacoustics.com
Thermoacoustic engines
Acoustic to electric conversion
Conversion mechanismns
Current limitations
Bi-directional turbines
Principle
Experiments
Design approach
30 oktober 2015 2
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 Temperature lift
Acoustic resonance and feedback circuit
Acoustic to electric conversion
Conversion of (thermo) acoustic power to electricity
Acoustic pressure amplituden Periodic force (F) n Periodic displacement (s)
Conversion mechanismns•Piezo electric•Electro magnetic
n Magneto Hydro Dynamic (MHD) fluid pistonn Linear alternator, solid piston
•Others……….
•Solid or fluid characterized by a high acoustic impedance•Acoustic impedance matching by resonance
n Mass-spring systemn Gas springn Mechanical springn Gravity
30 oktober 2015 3
0
Meanpressure
Pressureamplitude
T
Alternator TAP Star-engine qdrive
The origin of limitations
Scaling up in power
• Induction (dφ/dt)n Force (pressure amplitude)n Velocity amplituden Frequencyn Magnetic field
• Stroken Limited by springs
• Moving massn Inertancen Gas springs
• Clearance sealn Tigth tolerancen Loss proportional with 1 / freq
30 oktober 2015 4
m
F, s
gap
Dp
pa
Helium, P0 = 0.6MPa, dr=5%, Dp= 120mm∅, Lp = 40mm
High power application example
30 oktober 2015 5
3m
Conversion of industrial waste heat into electricity
Thermoacoustic power (TAP)
•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
nUpgrade waste heat above the pinch
•Gas liquefactionnStorage and transport of LNG
Balanced linear alternators
4 x 2 x 1.25kWe
High power application example
30 oktober 2015 6
Leassons learned from the TAP project in 2011 •Thermoacoustic energy conversion itself can be scaled up in power unlimited•Upscaling toward high power is limited by practical and by economic linear alternator issues
Practical issues• Piston stroke limited by stroke of the springs
• Sensitive to overload (varying load or input)
• Size and weigth of moving mass more than proportional with power (Larger TA system ⇒ lower frequency ⇒ less induction)
Economic issues • Cost > 3000 € / kW
• No mass production
• Per kW electrictricity relativelly large amont of magnetic materiaal
• Future availability and cost of raw materials for strong magnets (e.g. neodynium)
The TAP Linear alternator
Alternative acoustic to electric conversion
30 oktober 2015 7
Using the acoustic wave pressure component
• Convert periodic pressure variation into bi-directional linear motion (piston, membrane)
n Linear alternators
n MHD
n Piezo electric effect
n Others…….
Using the acoustic wave velocity component
• Convert bi-directional velocity into uni-directional rotation
n Bi-directional turbine
n Others……
0
Meanpressure
0
Acoustic wave motion
Pressureamplitude
Gas displacementamplitude
Bi-directional turbines
30 oktober 2015 8
Bi-directional turbines
Rotation is independent of flow direction
Know implementations •Lift based turbines
Wells turbine
Darrieus rotor (vertical axis wind turbine)
•Impulse based turbinesSavonious rotor
Axial impulse turbine
Radial impulse turbine
Existing technology used for oscillating water column (OWC) wave power plants (30-500kWe)
Bron: Limpet 500
Guide vanes
Rotor
Guide vanes
Air flow
Bi-directional turbines
30 oktober 2015 9
Rotor efficiencyn Fluid densityn Flow coefficient n Size (scale effect)
Power level• OCW plants
n Air at atmospheric pressure
n 5-50 kWe plants installed
• Acoustic power conversionn Gas at high elevated
pressuren Up to 1 kW tested (2013)n No scale or power limits
• Economics / productionn 130 €/kWe (# 1000)n Standard generatorn Plastic turbine
Water turbines• High density
Acoustic turbines• Large scale• high pressure
Acoustic turbines• Small scale• Atmospheric pressure
Oscillating water columnPower (OWC) plant• Large scale• Atmospheric pressure
Initial experiments
30 oktober 2015 10
Acoustic experiments on scale models
• Radiale impuls turbine • Axiale impuls turbine
Both manufactured in SLA-SMS 3-D printing.
brushless DC elektromotor used as generator
Observations:•Radial turbine
•Higher torque at lower rotational speed
•Axiale turbine•Lower torque at higher rotational speed
•Output power and efficiency of both embodiments not sensitive to acoustic frequency
Axial impuls turbine
Relation rotor efficency and frequency
Scaling experiment performed in the 100 kW TAP
30 oktober 2015 11
Linear alternator set replaced by radial bi-directional inpulse turbine
•Measured rotor efficiency of 75% for air at 0.8MPa and 16Hz oscillation frequency •Confirms that efficiency increase with fluid density
Radial impuls turbine(Drotor =300 mm)
Radial impuls turbine mounted in engine stage #1
Axial impuls turbine(Drotor =200 mm)
Design approach
Turbine act as a complex acoustic impedancen Inertance by acceleration in blade sections n Real part represent shaft power and losses
30 oktober 2015 12
20 40 60 80 1000
0.5
1
1.5
2
2.5
freq [Hz]
|Z| /
ρC
20 40 60 80 1000
10
20
30
40
50
60
70
80
90
freq [Hz]
angl
e Z
[deg
]
0000 Rpm1000 Rpm2000 Rpm3000 Rpm4000 Rpm4500 Rpm
Guide vanes
Rotor
Generator
Measured impedance of a 72mm∅ axial 4-stage turbine
Zin
2-stage turbine
Design approach
Coupling with the TA engine
• In series Inserted in the traveling wave feedback loopNo additonal tubingLow velocityLow rotational speed
• In Parallel n Connected by a T junction to the traveling
wave feedback loopn Additional tubingn Hellmholts type resonatorn High velocity n High rotational speed
30 oktober 2015
Bi-directional turbine Terminated with complex impedance
Bi-directional turbine
Terminated with Z ≈ ρ.c
Design approach
Turbine design using analytic expresions
• Flow coefficient φφ = gas velocity (va) / circumferencial speed (Ur)
• Torque coefficient CTCT = f (Re, shape, angle)
• Input coefficient CACA = f (Re, shape, angle, surface)
• Rotor efficiency ηR
• Typical Reynolds numbersOWC 104 < Re 5.104
High power TA turbine Re > 2.105
30 oktober 2015 14
0 1 2 3 4 50
2
4
6
8
10
φ = va/ UR
CTCA
Design approach
• Example of an input file for an axial
turbinen T0 = 300;
n P0 = 29e5;
n GasType = 'He';
n D0 = 0.050; % TAEC reference diameter
n V0 = 8; % input flow velocity amplitude at D0
n R0 = 0.040; % outer radius rotor
n R1 = 0.031; % inner radius rotor
n Lt = 0.015; % blade chord length
n B1 = 0.0012; % rotor blade thickness
n B2 = 0.0025; % distance between rotor blades
n z = 30; % number of blades
30 oktober 2015 15
24-Oct-2015 12:09:50
Data_file: STAGE axial turbine, v3
GasType = He
v0 = 8.00 m.s-1 (effective value)
Solidity = 1.02 -
P0 = 2.90 MPa
RP = 2400 Rpm
|Z| = 0.11 ρc
P_shaft = 48.21 W
P_ac = 67.85 W
Eff = 71.0 %
Conclusions (1)
• Thermoacoustic energy conversion can be scaled up in power to industrial power levels n Increase dimensionsn Lower frequency
• Linear alternators can not be scaled up accordingly for practical and economic reasons
• Search for an alternative approach by adapting bi-directional turbines from OWC power plants and converting the velocity component of the acoustic wave into rotation n Bi-directional turbines are proven technology for Oscillating Water Column power plants n Coupled to standard generators n No vibration issuesn Scalable
Experiments are performed to validated this approach and it is observed that • Turbine efficiency raise with fluid density (mean pressure) • Performance is maintained over a large frequency range (non-resonant)• No strict tolerances• Scalable• Ready for mass production (plastic moulding)
30 oktober 2015 16