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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Brush Seal to Hybrid Brush Seal ….to…

An engineered evolution:

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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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Labyrinth Seal3 teeth

Cantilever pad

TEST SEALS

HALO Seal

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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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TEST LABYRINTH SEAL

Cold clearance 2c =0.51 mm

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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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100°C

LEAKAGE: HALO Seal

PR: upstream pressure /ambient (exit) pressure

23.6 m/s

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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!

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QUESTIONS?Thanks to: • Turbomachinery Research Consortium for funding project• Advanced Technologies Group (Mr. John Justak) for donating HALO™ seal• SIEMENS Power Gen. for funding test rig construction.

Learn more at http://rotorlab.tamu.edu