Measurements Of Leakage and Force Coefficients in a Short Length Annular Seal Operating with a Gas in Oil Mixture

Transcription

1 2015 STLE Annual Meeting & Exhibition, May 17-21, 2015, Dallas, TX Measurements Of Leakage and Force Coefficients in a Short Length Annular Seal Operating with a Gas in Oil Mixture Luis San Andrés Mast-Childs Chair Professor Fellow STLE Q. Liu & X. Lu Graduate Research Assistants May 2015 Supported by TAMU Turbomachinery Research Consortium 1

2 Bubbly Mixture Annular Pressure Seals Justification Seals operate with either liquids or gases, but not both As oil fields deplete compressors work off-design with liquid in gas mixtures, mostly inhomogeneous. Similarly, oil compression station pumps operate with gas in liquid mixtures. The flow condition affects compressor or pump overall efficiency and reliability. Little is known about seals operating under 2-phase conditions, except that the mixture affects seal leakage, power loss and rotordynamic force coefficients; perhaps inducing random vibrations that are transmitted to the whole rotor-bearing system. 2

3 Subsea Application: Wet Gas Compression Brenne, L., Bjørge, T., Gilarranz, J., Koch, J., and Miller, H., 2005, Performance Evaluation of A Centrifugal Compressor Operating under Wet Gas Conditions, Proc. 34 th Turbomachinery Symposium, Houston, TX, pp. 111~120 Brenne, L., Bjørge, T., Bakken, L., and Hundseid, Ø., 2008, "Prospects for Sub Sea Wet Gas Compression," ASME Paper GT Bertoneri, M., Duni, S., Ransom, D., Podesta, L., Camatti, M., Bigi, M., and Wilcox, M., 2012, Measured Performance of Two-stage Centrifugal Compressor under Wet Gas Conditions, ASME Paper GT Vannini, G., Bertoneri, M., Del Vescovo, G., and Wilcox, M., 2014, Centrifugal Compressor Rotordynamics in Wet Gas Conditions, Proc. 43 rd Turbomachinery & 30 th Pump Users Symposia, Houston, TX. Bertoneri, M., Wilcox, M., Toni, L., and Beck, G., 2014, Development of Test Stand for Measuring Aerodynamic, Erosion, and Rotordynamic Performance of a Centrifugal Compressor under Wet Gas Conditions, ASME Paper GT Announce / assess the effects of two phase flow in wet gas compression: drop in efficiency and reliability, excessive vibration and rotordynamic stability. 3

4 Squeeze film dampers Background literature Experimental & Physical Modeling Tao, L., Diaz, S., San Andrés, L., and Rajagopal, K.R., 2000, "Analysis of Squeeze Film Dampers Operating with Bubbly Lubricants" ASME J. Tribol., 122. Diaz, S., and San Andrés, L., 2001, "Air Entrainment versus Lubricant Vaporization in Squeeze Film Dampers: An Experimental Assessment of their Fundamental Differences, ASME J. Eng. Gas Turbines Power, 123. Diaz, S., and San Andrés, L., 2001, A Model for Squeeze Film Dampers Operating with Air Entrainment and Validation with Experiments, ASME J. Tribol., Diaz, S., and San Andrés, L., 2002, Pressure Measurements and Flow Visualization in a Squeeze Film Damper Operating with a Bubbly Mixture, ASME J. Tribol., 124. Sponsored by National Science Foundation and TAMU Turbomachinery Research Consortium, June May

5 Literature: Two Phase Flow in Annular Seals Experimental Seals (two phase) Hendricks, R.C., 1987, "Straight Cylindrical Seals for High Performance Turbomachinery," NASA TP Iwatsubo, T., and Nishino, T., 1993, An Experimental Study on the Static and Dynamic Characteristics of Pump Annular Seals, 7th Workshop on Rotordynamic Instability Problems in High Performance Turbomachinery, Texas A&M University.. Computational Seals (two phase) Beatty, P.A., and Hughes, W.F., 1987, "Turbulent Two-Phase Flow in Annular Seals," ASLE Trans., 30. Arauz, G., and San Andrés, L., 1998, Analysis of Two Phase Flow in Cryogenic Damper Seals, I: Theoretical Model, II: Model Validation and Predictions, ASME J. Tribol., 120. Arghir, M., Zerarka, M., Pineau, G., 2009 "Rotordynamic Analysis of Textured Annular Seals with Mutiphase (Bubbly) Flow, Workshop : Dynamic Sealing Under Severe Working Conditions EDF LMS Futuroscope. NEED EXPERIMENTAL validation. San Andrés, L., 2012, Rotordynamic Force Coefficients of Bubbly Mixture Annular Pressure Seals, ASME J. Eng. Gas Turbines Power,

6 Experimental Seals (two phase) Mxx Iwatsubo, T., and Nishino, T., 1993, An Experimental Study on the Static and Dynamic Characteristics of Pump Annular Seals, 7th Workshop on Rotordynamic Instability Problems in High Performance Turbomachinery. Cxx Kxx NO description of water lubricated seal (L, D, c) or gas type.. Tests at shaft speed krpm and supply pressure= bar. Gas/liquid volume fraction =0, 0.25, 0.45, 0.70, gas volume fraction increases Stiffness, damping and mass coefficients decrease as gas volume fraction increases. 6

7 Motivation Application Subsea compression and pumping (wet compressors must operate with LVF up to 5%) Effect of two component flow on seal Leakage rate Dynamic force coefficients Stability Status of current research: Bulk-flow model available Lack of experimental validation 7

8 Overview of this work Design and construct test rig. Make oil-gas mixtures with liquid volume fraction (LVF) at inlet plane from 0.0~1.0. Measure flow rate thru seal for range of LVF & pressure supply/discharge = 1 to 4. Measure test system periodic forced response and perform parameter identification. room temperature 20 o C. Stationary (non-rotating) journal. 8

9 Wet Seal Test Rig Top plate Air-Oil Mixture Main frame Support pipe Shaker Stinger Bearing cartridge Thermocouple Accelerometer Rotor Shaker Dynamic pressure sensor Rotor Load cell Shaker Bearing Eddy current sensor seal clearance 9

10 Flows & Mixture Air Oil Inlet (ISO VG 10) Valve Air Inlet Valve Sparger (mixing) element Test seal section Oil P s /P a =1.5, inlet LVF= 2% 10

11 Seal cartridge L/D=0.36 Flow Diameter Length clearance Seal 127 mm (5in) 46 mm (1in) mm (5mil) Seal Supply pressure 1~3.5 bar Oil ISO VG 10 density 846 kg/m 3 viscosity 18 cp at 20ºC Air density viscosity 1.2 kg/m 3 at 1bar 0.02 cp at 20ºC, 1bar Rotor & journal 11

12 Flow Rate Measurement Flow rate of mixture vs. supply pressure 1.1 ~3.5bar (abs) Room temperature ~20ºC Liquid volume fraction (at supply pressure) at inlet: LVF= β = inlet Q l P Q+Q a l g P s Air Mass fraction is constant as there is no mass transfer between oil and air. Oil 12

13 Mass Flow Rate in Wet Seal mass flow rate Mass flow rate of mixture [kg/s] L/D=0.36 c=0.127 mm seal inlet LVF Measurement Prediction Liquid mass fraction ( ) is large even for small LVF because of large density ratio (oil/air)~200. Flow ranges from turbulent (pure air) to laminar (pure oil). Predicted flow ~ 10% lower than measured. P s /P a =3.5 Supply P S =3.5 bar(abs), ambient P a =1 bar(abs), (non-rotating) journal. Liquid mass fraction Reynolds #

14 Flow visualization in Wet Seal Top Seal land length= 46 mm ambient pressure P a =1 bar(abs), inlet temperature 20 o C. Non-rotating journal. Inlet LVF=0.45 P S =1.5 bar(abs) Top Bottom =0.45 L/D=0.36 c=0.127 mm Bottom P S =3.0 bar(abs) =0.45 Smaller bubbles with higher supply pressure

15 Force Coefficients in Annular Seals c D L rotor rotor P e stator P a Axial pressure field (liquid) W Axial velocity Y X Film thickness H=c+e X cos e Y sin Seal reaction force is a function of the fluid properties, flow regime, operating conditions and geometry. For small amplitudes of rotor lateral motion: forces are linearized with stiffness, damping and inertia force coefficients: P S F K K x C C x M M x X XX XY XX XY XX XY F K K y C C y M M y Y YX YY YX YY YX YY 15

16 Parameter Identification Model system (2-DOF): structure + seal EOM: Time Domain EOM: Frequency Domain Measure: (K +K )z+(c +C )z+(m +M )z=f S SEAL S SEAL BC SEAL K C M 2 K+ iωc-ω M z=f Load F=Fo sin( t) Displacement z, 2 H( ) z =F H( ) K+ iωc-ω M =F z 1 2 Re H ( ) K-ω M Im H ( ) ω C (?) Estimate Parameters: K, C, M

17 Applied load and seal motion X direction, frequency = 30 Hz 90 Load 50 Displacement Load (N) Load (N) inlet LVF 0% inlet LVF 4% Time (s) FFT 20 inlet LVF 0% 15 inlet LVF 4% Frequency (Hz) Displacement (um) Displacement (um) inlet LVF 0% inlet LVF 4% Time (s) FFT inlet LVF 0% inlet LVF 4% Unexplained drift at low frequencies Frequency (Hz)

18 Parameter Identification Instrumental Variable Filter Method (IVFM) (Fritzen, 1985, J.Vib, 108) Complex stiffness Re 2 H K M H Im (?) C Real(H) (MN/m) Hᵪᵪ Hᵧᵧ K - Mω² Frequency (Hz) Imaginary(H) (MN/m) P s /P a =2, inlet LVF 2% 20 Hᵪᵪ 16 Hᵧᵧ Frequency (Hz) Seal coefficients (K, C, M) SEAL = (K, C,M) (K, C, M BC ) S SEAL Test system (lubricated) Structure (dry)

19 Test System Dynamic Stiffness liquid volume fraction at inlet: β inlet =0.02 Real(H) (MN/m) Hᵪᵪ Hᵧᵧ K - Mω² Frequency (Hz) 2.0 = Supply pressure P S /ambient pressure P a inlet temperature 20 o C. (non-rotating) journal. K- 2 M fits well the test data. β inlet =0.04 Uncertainty ±0.7MN/m Real(H) (MN/m) Hᵪᵪ Hᵧᵧ K - Mω² Frequency (Hz)

20 Test System Quadrature Stiffness liquid volume fraction at inlet ( β inlet = (all air) (m m =6±0.8 g/s) β inlet = (m m =6±0.2 g/s) Imaginary(H) (MN/m) Imaginary(H) (MN/m) Hᵪᵪ Hᵧᵧ Frequency (Hz) Hᵪᵪ Hᵧᵧ Inlet LVF 0% Hᵪᵪ Hᵧᵧ 2.0 = Supply pressure P S /ambient pressure P a inlet temperature 20 o C. (non-rotating) journal. β inlet = (m m =7±0.2 g/s) Inlet LVF 4% Ima(H) shows damping is frequency dependent. Very little damping with all gas. Uncertainty: ±0.7MN/m Frequency (Hz) 20

21 Wet Seal Direct Damping C=Im(H)/ 100,000 β inlet = = Supply pressure P S /ambient pressure P a Stationary (non-rotating) journal. Cxx_seal (N-s/m) Cyy_seal (N-s/m) 10,000 1, Frequency (Hz) 100,000 10,000 β inlet =0.02 β inlet =0 (all air) β inlet =0.04 β inlet =0.02 1, β inlet = Frequency (Hz) liquid volume fraction at inlet 0% (all gas), 2%, 4%. Damping is frequency dependent. Small LVF causes damping to increase 20 fold w/r to air only. C XX & C YY differ due to uneven clearance and inhomogenous flow

22 Parameter Identification Seal mass and stiffness coefficients LVF at seal Liquid mass K XXseal K YYseal M XXseal M YYseal inlet fraction MN/m MN/m kg kg % 90% % 95% With mixture, CXX>CYY mixture is not evenly distributed in seal clearance. Liquid volume is larger in X direction than in Y direction

23 Completed work Assembled new test rig and trouble shoot. Generate mixtures and measure flow rates: LVF = 1% to 100% supply pressure up to 50 psig (3.5 bar abs) Rotor speed: stationary Forced response Installed shakers and performed single frequency dynamic load measurements Identification of force coefficients Visual inspection of bubbly mixture 23

24 Conclusion Mass flow rate through seal dictated by liquid content (density ratio ~ 200). Damping coefficients are frequency dependent. For operating conditions with a small volume fraction of oil in gas (4%), damping can be up to twenty times larger than that obtained for the pure gas condition. The effect of a few droplets of liquid on affecting the test system forced response is overwhelming. 24

25 Future Work Extend the range of LVF at seal inlet in tests to quantify its effect on force coefficients. Operate test seal rig with journal rotation (6 krpm) and with a higher supply pressure (6 bar). Benchmark bulk-flow model predictions 1. Extend existing predictive model 1 considering inhomogeneous flow. San Andrés, L., 2012, Rotordynamic Force Coefficients of Bubbly Mixture Annular Pressure Seals, ASME J. Eng. Gas Turbines Power, 134 (2), p

26 Acknowledgments Turbomachinery Research Consortium Turbomachinery Laboratory Staff and Students Questions (?) Learn more at 26