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LABYRINTH SEAL vs HALOTM SEAL:LEAKAGE AT HIGH TEMPERATURE
Luis San AndrésMast-Childs Chair Professor
Presentation to Alstom Power
Based on GT2014-25572
Jan 8, 2015
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OBJECTIVES & TASKS
• To measure leakage in two test seals:• Supply pressure (upstream) from 1 bar to 7 bar.• Air inlet temperature from 30ºC to 300ºC.
• To measure drag torque from each seal.
Industrial gas and steam turbine OEMs interested in benchmarking novel seal technologies against (traditional) labyrinth seal to realize benefits and to ensure potential gains.
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Labyrinth SealAdvantages .•Non-contacting.
• Wide range of pressures, temperatures, and shaft speeds
• Inexpensive.
Disadvantages
• Leakage depends on clearance
• Inevitable wear (enlarges clearances) and worsens leakage.
• Long seals lead to instability i.e. large cross-coupled stiffness.
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Hydrostatic Advanced Low Leakage Seal
Advantages .
• Low leakage.
• Radial compliance and stiff in axial direction.
• Pads generate hydrodynamic wedgeseparating seal from rotor (non-contacting).
Disadvantages
• Difficult to manufacture (EDM).
• Not many commercial applications.
• Expensive.
HALOTM seal
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Justak, J., 2013, “Hydrogen Compressor Seal Case Study,” Proc. 42nd Turbomachinery Symposium, Texas A&M University, Houston, TX, USA, Sept 30-Oct 3.
Applications of HALO Seal
Delivered HALO seals to replace 4 interstage, 5 impeller eye, and buffer gas seals for a hydrogen compressor.
During start up and run in, compressor did not experiencevibration on the way up to full speed.
At full speed the compressor was 20% more efficient than with the labyrinth seals.
By 09/2013, the compressor was operating for 6-months, 24/7.
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Heater
Exhaust duct
Air pressurization cylinder
Motor Test seal Roller bearings
cm
50 25 75 0
Flow in
Flow out
Rotor
Voltage Power OutputHeater 240 V 12 kW 300°CMotor 90 V 850 W 3,000 rpm
Maximum
TEST FACILITY
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TEST FACILITY
Maximum 300°C
1 Tapered roller bearings 7 Quill shaft
2 Shaft 8 Flexible coupling
3 Disk 9 Test seal
4 Pressure vessel 10 Metal Mesh Foil Bearing
5 Air inlet 11 Position rods
6 Motor 12 Eddy current sensors (X and Y directions)
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TEST RIG
Hot air IN
Test seal
Air OUT
Disc & Shaft
Air Constant 287 J/kg-K
Supply Pressure, Ps 101 kPa - 707 kPa
Inlet Temperature, Ts 303°K - 573°K
Exhaust Pressure, Pa 101 kPa
Ambient Temp., Ta 303°K
Shaft speed Tip speed (OD)
1000 rpm 8.7 m/s
2000 rpm 17.5 m/s
3000 rpm 26.2 m/s
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Bearing assembly
Hot air inlet100 psig (7 bar) max
Disk
Test seal
Metal mesh
Journal
Eddy current sensors
Support rod
Support rod
Shaft
TEST RIG: gas flow paths
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TEST SEALS DIMENSIONS AND PROPERTIESSeal Dimensions and Properties Labyrinth Seal HALOTM Seal Seal Material 4140 Steel Inconel 718 Linear Coefficient of Thermal Expansion, α 11.2 10-6/°C 12.0 10-6/°C Outer Diameter, SOD 183.11 mm 183.05 mm Inner Diameter, SID (Upstream) 167.36 mm 167.28 mm Seal Axial Length, l 8.40 mm 8.48 mm Number of Teeth 3 Teeth Tip Width 0.17 mm Number of Cavities 2 Cavity Depth 3.0 mm Number of Pads 9 Pad Allowable Radial Movement 0.27 mm Pad Axial Length, l 8.05 mm Pad Arc Length (40°) 58.42 mm Disk Material 4140 Steel 4140 Steel Linear Coefficient of Thermal Expansion, α 11.2 10-6/°C 11.2 10-6/°C Outer Diameter, D 166.85 mm 166.85 mm Disk Thickness 44.45 mm 44.45 mm Diametral Clearance (Cd=SID-D) 0.51 mm 0.43 mm Uncertainty in Lengths ± 0.01 mm ± 0.01 mm
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TEST RIG: TEMPERATURE MEASUREMENTS [2]
0
50
100
150
200
250
300
350
0 60 120 180
Tem
pera
ture
[°C
]
Time [min]
[2] Ashton, Z., 2009, "High Temperature Leakage Performance of a Hybrid Brush Seal Compared to a Standard Brush Seal and a Labyrinth Seal," M.S. thesis, Texas A&M University, College Station, TX.
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Flow rate increases with
pressure and decreases as air
inlet temperature
increases
PR: upstream pressure /ambient (exit) pressure
300°C
LEAKAGE: Labyrinth Seal
Choke region 17.5 m/s
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TEST HALO SEAL
0 2010
mm
Direction of flow
Direction of flow
HALO seal
Cold clearance 2c =0.43 mm
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HALO SEAL: CLEARANCE MEASUREMENTS [*]
Seal clearance decreases from 0.20
mm (cold) to 0.03 mm at a
pressure ~1.7 bar.
30ºC
[*] San Andrés, L., and Ashton, Z., 2009, "Monthly Report No. 16: May," Proprietary Technical Report to Siemens Power Gen., Turbomachinery Laboratory, Texas A&M University.
HALO seal is a
clearance control
element.
19No rotor speed
Compare leakage from two seals
HALO seal leaks a
fraction of labyrinth
seal.
Best at high pressures
when choking.
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Compare LEAKAGES: define flow factor
Flow factor
DPTm
s
Delgado & ProctorTo compare the leakage performance of different seal types with dissimilar operating conditions and geometry.
AIAA No. 2006-4754
=1.89 for air
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FLOW FACTOR: LABYRINTH SEAL
Flow factor removes effect of
temperature and is
independent of upstream
pressure after flow
chokes.Predictions are
good.
Flow factor
DPTm
s
300°C
Choke region
Predictions: Model of Thorat, M. R., 2010
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FLOW FACTOR: HALO SEAL
Flow factor decreases
above choke region
because clearance decreases
as pressure drop
increases
Flow factor
DPTm
s
100°C
Choke region
23.6 m/s
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No rotor speed
Compare flow factor from two seals
HALO seal has lower flow
factor than the labyrinth
seal (~1/2 to 1/5)
• HALO seal is +effective
in controlling
leakage
Flow factor
DPTm
s
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• Flow factor characterizes well leakage of both test seals operating at high temperature (300°C) and supply pressure (~4 bar).
• To 300°C, the HALO seal leaks 50% or less than the labyrinth seal. For pressure ratios (Ps/Pa) > 3.0, the novel seal leaks 70% or less than a labyrinth seal does.
• Shaft speed affects little the seals’ leakage (tip speed max = 25 m/s).
• Both seals offer similar drag torque (not shown).
CONCLUSIONS
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HALO™ Seal
Hybrid Brush Seal
0
5
10
15
20
25
30
35
40
1.0 2.0 3.0 4.0 5.0 6.0Pressure Ratio [Ps/Pe]
Flow
Fac
tor [
kg-K
0.5 /(M
Pa-m
-s)]
Labyrinth SealBrush SealHybrid Brush SealHALO™ Seal
Temperature (300 °C)
Flow factor
DPTm
s
Compare leakage from four seal types
[*] San Andrés, L., and Ashton, Z., 2009, "Proprietary Technical Report to Siemens Power Gen., Turbomachinery Laboratory, Texas A&M University.
2009 (Siemens Project)
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Funding to date ($279,806)
Siemens32525/3465AA
$106,950 High temperature Hybrid Brush Seal 10/01/076/30/09
TRC32514/1519 3S
$74,863 High Temperature Low Leakage Seals 08/01/10 08/31/13
TRC32514/1519/S4
$22,000 Stiffness and Damping Coefficients of Brush Seals with Reverse Rotation Ability
07/15/04-06/30/05
Siemens32525/34650
$ 75,993 Brush Seals with Reverse Rotation 01/01/06-09/30/07
ATG donated brush seal, hybrid brush seals and HALO seals
TRC: Turbomachinery Research Consortium funds graduate students mainly.
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• Revamp test rig to increase rotor speed for more realistic operating conditions: 15 krpm (120 m/s).
• Measure stiffness and damping coefficients of HALO seal over a range of operating conditions (air pressure and temperature and shaft speed) and compare to predictions.
Future Improvements
0 2010
mm
Direction of flow
Direction of flow
HALO seal
Sponsors sought!