LEAKAGE FOR AN ALL-METAL COMPLIANT GAS SEAL OPERATING...
Transcript of LEAKAGE FOR AN ALL-METAL COMPLIANT GAS SEAL OPERATING...
LEAKAGE FOR AN ALL-METAL COMPLIANT GAS SEAL OPERATING AT HIGH TEMPERATURE
Alain AndersonGraduate Research Assistant
Texas A&M UniversityTurbomachinery Laboratory Mechanical Engineering Department
Work supported by the TAMU Turbomachinery Research Consortium
2013 STLE Annual MeetingDetroit, Michigan, May 5-9, 2013
Luis San AndrésMast-Childs ProfessorFellow STLE
Paper number ??
JUSTIFICATIONTRENDS IN HIGH PERFORMANCE TURBOMACHINERY:
- Compact units (reduce axial length)- Extreme operating temperatures and pressures- Need for higher efficiency & reliability
CONSEQUENCES (as related to sealing):• Large pressure differentials create large forces that may
buckle flexible element seals• Tighter clearances lead to increased wear and drag• Thermal and centrifugal growth must be accounted for in
the design and operation of seals
OBJECTIVES & TASKS
• To quantify leakage of two test seals varying:• Supply pressure (upstream) from 1 bar to 8 bar (max)• Air inlet temperature from 30ºC to 300ºC
• To determine the effect of rotor speed in terms of leakage
Industrial gas turbine manufacturers interested in benchmarking novel seal technologies against (traditional) labyrinth seal to realize benefits and to ensure potential gains.
Labyrinth SealAdvantages
•Non-contacting
•Operates at a wide range of pressures, temperatures, and speeds
•Inexpensive
Disadvantages
•Leakage largely dependent on clearance
•Inevitable wear (enlarges clearances) and worsens leakage
•Long seals lead to instability i.e. large cross-coupled stiffness
Hydrostatic Advanced Low Leakage Seal
Advantages
• Low leakage
• Radial compliance and stiff in axial direction
• Pads generate hydrodynamic wedge separating seal from rotor (non-contacting)
Disadvantages
• Difficult to manufacture (EDM)
• Unproven, except for military
• Expensive
HALO seal
•Chupp et al. review sealing in turbomachinery, detail strengths and weaknesses of most seal types.• Delgado and Proctor measure leakage and power loss in a labyrinth seal, brush seal, and annular seal. Introduce flow factor:
•San Andrés and Ashton compare measured leakage for a labyrinth seal, a brush seal & a hybrid brush seal at high temperature (300°C).
LITERATURE REVIEW: Annular Seals(AIAA J. Propul. Power, 2006)
(Tribol. Trans., 2010)
(AIAA No. 2006-4754)
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•San Andrès et al. measure leakage and power loss in a Hybrid Brush Seal. HBS has ~ 36% less leakage than a shoed brush seal.
•Delgado and San Andrès measure leakage and structural characteristics of a shoed-brush seal.
•Justak and Doux introduce a novel self-acting compliant seal design and discuss CFD and experimental results.
•Justak unveils the HALO® seal
LITERATURE REVIEW: Non-contacting Seals
(U.S. Patent 7,896,352)
(Sealing Technol., 2005)
(ASME GT2008-50532 )
(ASME GT2009-59683)
EXPERIMENTAL FACILITY
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
EXPERIMENTAL FACILITYMaximum
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)
Specific Gas Constant 287 J/kg-K
Supply Pressure, Ps 101 kPa - 808 kPa
Inlet Temperature, Ts 303°K - 573°K
Exhaust Pressure, Pa 101 kPa
Ambient Temperature, Ta 303°K
Bearing assembly
Hot air inlet~100 psig
(7 bar) max
Disk
Test seal
Metal mesh
Journal
Eddy current sensors
Support rod
Support rod
Shaft
Seal Dimensions and Properties Labyrinth Seal Labyrinth Seal HALOTM SealSeal Material Aluminum Steel SteelLinear Coefficient of Thermal Expansion, α
23.6 10-6/°C 11.2 10-6/°C 12.0 10-6/°C
Outer Diameter, SOD 183.20 mm 183.11 mm 183.0 mmInner Diameter, SID (Downstream) 167.85 mm 167.36 mm 167.2 mmSeal Axial Length, l 8.40 mm 8.40 mm 8.5 mmNumber of Teeth 3 3Teeth Tip Width 0.17 mm 0.17 mmNumber of Cavities 2 2Cavity Depth 3.0 mm 3.0 mmNumber of Pads 9Pad Allowable Radial Movement 0.25 mmPad Axial Length, l 8.0 mmPad Arc Length (40°) 57.4 mmDisk Material 4140 Steel 4140 Steel 4140 SteelLinear Coefficient of Thermal Expansion, α
11.2 10-6/°C 11.2 10-6/°C 11.2 10-6/°C
Outer Diameter, D 166.81 mm 166.81 mm 166.81 mmDisk Thickness 44.45 mm 44.45 mm 44.45 mmDiametral Clearance (Cd=SID-D) 1.04 mm 0.55 mm 0.40 mmUncertainty in Lengths ± 0.026 mm ± 0.025 mm ± 0.025 mm
TEST SEALS DIMENSIONS AND PROPERTIES
No Rotor speed
LEAKAGE: Labyrinth Seal
Flow rate increases with pressure and decreases as air inlet temperature
increases due to change in gas density
PR: upstream pressure /ambient (exit) pressure
Labyrinth sealCd=1.04 mm
Labyrinth sealCd=0.55 mm
choked flow
No Rotor speed
LEAKAGE: HALO Seal
PR: upstream pressure /ambient (exit) pressure
Flow rate increases little with pressure and
decreases as air inlet temperature increases
due to reduction in clearance and changes
in gas density
choked flow
HALO seal, Cd=0.4 mm
HALO seal is a clearance controlled seal. Clearance reduces with supply pressure
FLOW FACTOR: Labyrinth Seal
No Rotor speed
Flow factor shows little temperature dependency
& is independent of supply pressure after
flow chokes.
PR: upstream pressure /ambient (exit) pressure
Labyrinth sealCd=1.04 mm
Labyrinth sealCd=0.55 mm
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No Rotor speed
FLOW FACTOR: HALO Seal
Inlet temperature has no effect on flow factor,
and decreases due to the constant mass
flow rate with increasing supply
pressure.
PR: upstream pressure /ambient (exit) pressure
choked flow
HALO seal
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Compare leakage from seals
HALO sealCd=0.4 mm
Labyrinth sealCd=1.04 mm Labyrinth seal
Cd=0.55 mm
Max. air temperature (300ºC), No rotor speed
Max. air temperature (300ºC) No rotor speed
Compare flow factors•Air temperature
affects little the seals’ flow factor.
•HALO seal has low flow factor, ~
¼ of LS with Cd=1.04 mm,
and ½ or less of LS with Cd=0.55
mm
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HALO sealCd=0.4 mm
Labyrinth sealCd=1.04 mm
Labyrinth sealCd=0.55 mm
LABY SEAL: OPERATION WITH ROTOR SPEED100ºC 300ºC
(At low temperature <100ºC) Rotor speed has negligible effect on leakage for the labyrinth seal. At 2.7 krpm, tip speed = 23.6 m/s
Flow factor
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Labyrinth sealCd=0.55 mm
Labyrinth sealCd=0.55 mm
Add slide of predictions vs test data for LabySeal
Add slide of clearance measurement in HALO (Ashton)
• Flow factor characterizes well the leakage of the test seals operating at high temperature (300°C) and supply pressure (~8 bar abs).
• Without rotor speed, the HALO seal shows less leakage than labyrinth seals, ½ to ¼ for small and (~25%) and steel labyrinth seal (~50%).
• Rotor speed decreases leakage at high temperature (300°C) for the labyrinth seal.
CONCLUSIONS
THANK YOU!
QUESTIONS?
Thanks to: • Turbomachinery Research Consortium for funding the project.• Advanced Technologies Group (Mr. John Justak) for donating HALO™ seal
Learn more at http://rotorlab.tamu.edu
• Modify test rig to increase rotor speed for more realistic leakage measurements.
• Measure structural stiffness and damping coefficients of HALO seal. Identify seals rotordynamic coefficients over a range of operating conditions (air pressure and temperature and shaft speed) and compare to predictions.
Measure leakage of HALO seal at rotor speeds up to 15 krpm
Future Improvements
0 2010
mm
Direction of flow
Direction of flow
HALO seal