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

Test seals

Labyrinth Seal3 teeth

HALO SealCantilever pad

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