Luis San Andrés TRC San Andres... · 2020-06-27 · 1 LEAKAGE AND ROTORDYNAMIC FORCE COEFFICIENTS...
Transcript of Luis San Andrés TRC San Andres... · 2020-06-27 · 1 LEAKAGE AND ROTORDYNAMIC FORCE COEFFICIENTS...
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LEAKAGE AND ROTORDYNAMIC FORCE
COEFFICIENTS OF A THREE-WAVE
(AIR IN OIL) WET ANNULAR SEAL:
MEASUREMENTS AND PREDICTIONS
Xueliang LuGraduate Research Assistant
Texas A&M University
Luis San AndrésMast-Childs Chair Professor
Fellow ASME
Funded by Turbomachinery Research
Consortium
accepted for
journal publication
Proceedings of ASME Turbo Expo 2018: Turbomachinery Technical
Conference and Exposition, June 11-15, 2018, Oslo, Norway
Paper GT2018-75200
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Annular Pressure Seals
Seals in a Multistage Centrifugal Pump or Compressor
Seals (annular, labyrinth or textured) separate regions of high pressure
and low pressure to minimize leakage (secondary flow); thus
improving the overall efficiency of a machine extracting or delivering
power to a fluid.
Impeller eye or
neck ring sealBalance piston seal
Inter-stage
seal
• Wet gas compression and multiphase oil boosting can
save up to 30% CAPEX when compared with a L/G
separation station.
• Subsea facilities must handle gas in liquid mixtures with
a varying gas content:
Wet gas compressor: LVF < 5%
Multiphase pump: 0< GVF< 100%
Justification subsea facilities
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Need of concerted effort to quantify effect
of two phase flow in sealing components
The aims are to improve reliability and to
reduce operating costs.
Prior Work Apps
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Vannini et al., 2016, “Experimental Results and CFD Simulations of Labyrinth and Pocket Damper
Seals for Wet Gas Compression,” ASME J. Eng. Gas Turb. Power, 138.
0.45 X SSV increases in
magnitude with LVF
13.5 krpm, 10 bar
Balance piston:
Labyrinth sealFluids:
Air and water
Rotor lateral vibration
LVF: 0~3%
Trapped liquid in seal
rotates with great
momentum and causes
0.45X vibes.
1 X
0.45 X
Two-phase flow in a wet gas compressor
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Vannini et al., 2016, “Experimental Results and CFD Simulations of Labyrinth and Pocket Damper
Seals for Wet Gas Compression,” ASME J. Eng. Gas Turb. Power, 138.
13.5 krpm, 10 bar
Balance piston:
Pocket damper
seal (PDS)
Rotor lateral vibration
0.45 X SSV reduces from 20 μm
to a few microns.
Liquid does not accumulate
in PDS, thus mitigating SSV.
1 X
0.45 X
Two-phase flow in a wet gas compressor
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Helico-axial pump (1.5 to 4.6 krpm)
Rotor SSV appears under some
two-phase flow conditions : low
differential pressure with a
high-viscosity mixture.
Bibet, P. J., et al., 2013, "Design and Verification Testing of a New Balance Piston for High Boost
Multiphase Pumps," Proc. 29th International Pump User Symposium, Houston, TX.
Bibet et al. (2013)
Two-phase flow in a Multiple Phase pump
Pump operates stable with liquid.
(600 cPoise)
When vibrations occur, seal whirl
frequency ratio > 1.0.
high amplitude
SSVs
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Childs and students (2012-2017)
Brief Review of Research on Wet Seals at TAMU
San Andrés and students (2014-present)
Measures leakage and rotordynamic force coefficients of wet seals with
an air in silicon oil mixture. GVF: 0 10%, LVF: 0 8%. Max pressure: 70
bar, shaft speed 20 krpm (RΩ=96 m/s)
J. Eng. Gas Turb. Power, 2017, v. 139
ASME J. Eng. Gas Turb. Power, 2018
ASME GT2017-63254 (San Andrés and Lu) S&D Best Paper Award
Quantifies leakage and dynamic force coefficients of wet seals [five types]
with an air in ISO VG10 oil mixture. GVF: 0 1, Max supply pressure: 5
bar, shaft speed: 5.2 krpm (RΩ=35 m/s).
Tribol. Trans., 2016 2018 ATPS/TPS
Application: Subsea multiphase pumps and wet gas
compressors
Overview of GT2018-75200
• Make oil-gas mixtures with inlet GVF = 0.0 0.9.
• Measure flow rate for range of GVF & pressure
supply/discharge = 1 3.5.
• Measure test system periodic forced response and perform
parameter identification.
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TYPICAL OPERATION RANGE FOR ELECTRICAL SUBMERSIBLE PUMP
• Vertical pumps (with plain bushings) operate w/o a radial
load, hence are prone to show SSVs.
• A three-lobe bearing generates a centering stiffness to
stabilize a pump.
Does a three-wave seal operate stably with either a
gas or a liquid or a mixture?
• Generates centering stiffness in (unloaded)
vertical pump.
• Easy to fabricate with low cost. 10
Three-wave seal (from Dimofte in early 1990’s)
Diameter D = 2R 127 mm
Length L 46 mm
Number of waves 3
Max clearance cmax 0.274 mm
Min clearance cmin 0.108 mm
Mean Clearance
cm= ½(cmin + cmax)0.191 ± 0.004 mm
Wave amplitude
ew = cmax - cm
0.083 mm
εw = ew/cm =0.43
Benefits
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Three-wave seal
Measure wall thickness ht
c = ½ OD - ht – ½ D
cm= 0.191 mm
D: shaft diameter
Design clearance Measured clearance
Test seal
Measure OD
Clearance:
Test Rig at TAMU
Turbo Lab
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Air InletOil Inlet
(ISO VG 10)
Test seal
section
Valve
Valve
Sparger
(mixing)
element
Wet seal test rig shaft speed: 3.5 krpm (23.3 m/s)
GVF at inlet:
/
/in
g a s
l g a s
Q P P
Q +Q P P
α : Gas volume fraction
Ps: pressure at seal inlet plane
Pa: ambient pressure= 1 bar(a)
Qg: gas flow rate at Ps
Ql: liquid flow rate
Supply pressure (Ps) 1.0~3.5 bar (abs)
Oil ISO VG 10
density(ρl) 830 kg/m3
viscosity (μl) 10.6 cP at 34 ºC
Air density (ρga) 1.2 kg/m3 at 1bar
viscosity(μga) 0.02 cP at 20 ºC
Section A-A
Stinger Y
Stinger X
Ω
Seal element
Journal
housing
Support rod
(90° apart, four)
Y
X0
Shaker Y
Shaker XSeal
Top lidSeal
housingSeal element
Load cell
Accelerometer
Displacement
sensor
Journal
Shaft
Shaker
stinger
Centering
bolts
Support
rod
Wet seal test rig
Stinger
Top journal speed, Ωmax 3.5 krpm
Rotor surface speed, ½DΩmax 23.3 m/s
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A A
Centering bolts
Leakage for uniform
clearance seals and wavy-seal
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#1 c1=0.203 mm
#2 c2=0.274 mm
Paper GT2017-63254
#3 cm=0.191 mm
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
0.00 0.20 0.40 0.60 0.80 1.00
Three-wave seal
(4 krpm)
Three wave seal
(0 rpm)
Plain seal-1, (0 rpm)
Cseal#1 = 0.203 mm; Cseal#2 = 0.274 mm; Cwavy-seal = 0.191 mm
Mass f
low
/ l
iqu
id m
ass f
low
Plain seal-2
(0 rpm)
Gas volume fraction at seal inlet
Leakage for all seals shows
same trend as GVF
increases it drops!Three-wave seal leaks a little
more.
Predictions agree with test
data.
Leakage (Mixture) gas volume fraction increases
mixture
liquid
mm
m
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Normalized with respect to liquid
(GFV=0)
Seal Dynamic Force
Coefficients
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#3
Three-wave seal cm=0.191 mm
Dynamic load tests
Excite test system
with periodic loads
and measure test
system forced
response and
perform parameter
identification.
room temperature 20oC.
journal speed: 3.5 krpm(RΩ: 23 m/s)
Inlet GVF: 0 to 0.9
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Seal reaction force is a function of the
fluid properties, flow regime, operating
conditions and geometry.
For small amplitudes of rotor
motion, the force is represented
with stiffness, damping and inertia
force coefficients:
X
Y
F K k x C c x M 0 x
F k K y c C y 0 M y
Dynamic force coefficients
X
Y
K k C cF x x
F k K y c C y
For two-
phase flow
or a gas
frequency dependent
EOM: Time Domain
' ')SEAL SEAL SEAL S S SK z+C z+M z = F-M a-(K z C z
Relative displacement Absolute acceleration Absolute displacement
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Model system (2-DOF): structure + SEAL
Measure:
Load F=Fo sin(t)
Displacement z,
acceleration a
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Structure (pipe) stiffness,
Ks = 690 kN/m
Structure damping,
Cs= 0.2 kN.s/m
Housing mass & seal
MBC = 7 kg
Test rig structure parameters
Dry system
natural frequency,
fn= 50 Hz
& damping ratio, ξ = 4.5 %
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Model system Dynamic Complex Stiffness (H)
'S S S F-M A- K + C z H ziω
( ) ( )
( ) ( )
Re
Im
H K
H C
Parallel to rotor center displacement
Parallel to rotor center velocity
EOM: Frequency Domain
Components of complex dynamic stiffness H
functions of frequency ().
Direct dynamic complex stiffness (MN/m)Ps/ Pa = 2.5.
3.5 krpmGVF = 0
GVF = 0.9
GVF=0: K is a parabolic
function of frequency.
GVF>0: K does not reduce
with frequency.
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GVF = 0.2
Frequency (Hz)
Frequency (Hz)
Frequency (Hz)
Cross coupled complex stiffness (MN/m)Ps/ Pa = 2.5.
3.5 krpm
Re(HXY) & - Re(HYX) decrease
with GVF. Peculiar dip at
ω Ω or ω ωn
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GVF = 0
GVF = 0.2
GVF = 0.9
Frequency (Hz)
Frequency (Hz)
Frequency (Hz)
Quadrature dynamic stiffness (MN/m)Ps/ Pa = 2.5
3.5 krpmGVF = 0 GVF = 0.2
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GVF = 0.9
Im(H)= C is proportional
to frequency.
Damping C decreases as GVF
increases.
Frequency (Hz)Frequency (Hz)
Frequency (Hz)
Effective damping (kN.s/m)
Ps/ Pa = 2.5.
3.5 krpm
Ceff =(C - k/ω)
Ceff reduces with increase in GVF.
Cross frequency: 0.46X→ 0.43X
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GVF = 0
GVF = 0.2
GVF = 0.9
Frequency (Hz)
Frequency (Hz)
Frequency (Hz)
Compare test results for plain
cylindrical seals and three-wave seal
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#1 & # 2
Plain sealsc1=0.203 mm, c2=0.274 mm (worn)
#3
Three-wave seal cm=0.191 mm
Large uniform clearance seal
emulates a seal worn condition
Ps/ Pa = 2.5 & 3.5 krpm
Direct dynamic stiffness K (MN/m)
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Symbols: test results Lines: predictions
Three wave seal (#3) shows largest
K (promotes static stability).
Worn seal (#2) shows lowest K.
K : soft to hard as GVF increases
lesser added mass!
Ps/ Pa = 2.5; 3.5 krpm
GVF = 0.9
GVF = 0.0
GVF = 0.2
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Direct damping coefficient C (kN.s/m)
Worn seal (#2) shows
smallest damping.
Three wave seal (#3) shows
largest damping.
C drops with GVF
C ~ Cpl (1-GVF)
Damping is frequency
independent
Symbols: test results
Ps/ Pa = 2.5; 3.5 krpm
For stability, Ceff >0 is a must.
Increase in GVF Ceff drops.
Cross frequency drops from ~
½ X to lower magnitude.
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Effective damping (kN.s/m) Ceff =C –k /ω
Symbols: test results Lines: predictions
Ps/ Pa = 2.5; 3.5 krpm
GVF = 0.0
GVF = 0.2
GVF = 0.9
Test data and model to become a reference for the design of seals in
electrical submersible pumps.
(a) Three wave seal leaks more than a plain seal but produces largest direct
stiffness K.
(b) Mass flow continuously drops with an increase in gas volume fraction (GVF).
(c) Force coefficients are frequency dependent for operation with gas/oil
mixture.
(d) Three wave seal cross –coupled stiffness k decreases with both frequency
and GVF.
(e) Direct damping C decreases with GVF C~Cl (1-GVF)
(f) Effective damping Ceff increases with frequency and drops with GVF. Cross
over frequency is ~ ½ X.
(g) Air injection produces a hard centering stiffness.
(h) Future work will focus on non-homogenous flow models for seals supplied
with air/liquid mixtures with large GVF conditions.
Conclusion
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Paper GT2018-75200
For more test results (6 seals) please read our ATPS/TPS papers
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Six test seals
Smooth surface
plain seal x 2:Nominal c and worn (>c)
Three-wave seal:Large dynamic stiffness
Groove seal: Typ for pumps (turbulent
flow)
Step clearance
seal x 2: Often used in water
turbines/pumps.
Plain seals #1 & 2:(c1= 0.203 mm, c2 = 0.274 mm)
#3
Three-wave seal(cm=0.191 mm)
#4
Grooved seal (cr=0.211 mm, dg=0.543 mm,
lg=1.5 mm, ll=0.904 mm,
Ng=14)
#5
Upstream step clearance (cT=0.164mm, cB=0.274 mm,
LT=0.11L).
#6
Downstream step
clearance (cT=0.274 mm, cB=0.164 mm,
LT=0.82L).
San Andrés, L., Lu, X., and Zhu, J., 2018, “On the Leakage and Rotordynamic Force Coefficients of Pump
Annular Seals Operating with Air/Oil Mixtures: Measurements and Predictions,” Proc. 2nd Asia
Turbomachinery & Pump Symposium, Singapore, Mar. 13-15.
Clearance c~0.2 mm
Acknowledgments
Turbomachinery Research Consortium
Questions (?)
Learn more at http://rotorlab.tamu.edu
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Backup slides
Flow visualization in
upstream pipe, seal
clearance and
downstream pipe
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D = 26 mm
Mixture in upstream pipe GVF = 0.5. Ps =2.5 bara
Mixture in seal inlet GVF = 0-0.9. Ps/Pa=2.5. 0 rpm
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Mixture in downstream pipe