Leakage and Dynamic Force Coefficients of a Pocket Damper Seal Operating Under a Wet Gas Condition: Tests Versus Predictions

2019 ◽  
Vol 141 (11) ◽  
Author(s):  
Jing Yang ◽  
Luis San Andrés ◽  
Xueliang Lu
Keyword(s):  
Test Data ◽  
Mass Flow ◽  
Mass Fraction ◽  
Dynamic Stiffness ◽  
Dynamic Force ◽  
Rotor Speed ◽  
Force Coefficients ◽  
Supply Pressure ◽  
Liquid Mass ◽  
Wet Gas

AbstractHigh-performance centrifugal compressors presently favor pocket damper seals (PDSs) as a choice of secondary flow control element offering a large effective damping coefficient to mitigate rotor subsynchronous whirl motions. Current and upcoming multiple-phase compression systems in subsea production facilities must demonstrate long-term operation and continuous availability, free of harmful rotor instabilities. Plain annular seals and labyrinth (LABY) seals are notoriously bad choices, whereas a PDS, by stopping the circulation of trapped liquid, operates stably. This paper presents experimental and computational fluid dynamics (CFD) results for the leakage and dynamic force coefficients obtained in a dedicated test facility hosting a fully partitioned PDS (FPPDS), four ribbed and with eight pockets per cavity. The test PDS, operating at a rotor speed 5250 rpm (surface speed 35 m/s) and under a supply pressure/discharge pressure ratio up to 3.2, is supplied with a mixture of air and ISO VG 10 oil whose maximum liquid volume fraction (LVF) is 2.2%, equivalent to a liquid mass fraction of 84%. When supplied with just air (dry condition), the measured leakage increases nonlinearly with supply pressure. Under a wet gas condition, the recorded mass flow increases on account of the large difference in density between the liquid and the gas. CFD-derived mass flow rates for both dry and wet gas conditions agree with the measured ones. The test dry gas PDS produces a direct dynamic stiffness (HR) increasing with frequency, whereas the direct damping (C) and cross-coupled dynamic stiffness (hR) coefficients remain relatively constant. The CFD-predicted damping agrees best with the test C albeit overpredicting HR at low excitation frequencies and hR at all frequencies (<175 Hz ∼ twice rotor speed). Under a wet gas condition with LVF  =  0.4%, the test force coefficients show great variability over the excitation frequency range; in particular, HR < 0, though growing with frequency due to the large liquid mass fraction. The CFD predictions, on the other hand, produce a dynamic direct stiffness HR > 0 for all frequencies. Both experimental hR and C for the wet gas PDS are larger than their counterparts for the dry gas seal. The CFD-predicted C and hR, wet versus dry, show a modest growth, yet remaining lower than the test data. The CFD-derived flow field for a wet gas condition shows that the seal radial partition walls (ridges) reduce the circumferential flow velocity and liquid accumulation within a pocket. Both the test data and the CFD prediction show that the magnitude of the flexibility function for the PDS test system reduces when the two-component mixture flows through the seal, hence revealing the additional effective damping, more pronounced for the test data rather than that from the predictions. Further work, experimental and CFD based, will continue to advance the technology of wet gas seals while bridging the gap between test data and computational physics model simulations.

Leakage and Dynamic Force Coefficients of a Pocket Damper Seal Operating Under a Wet Gas Condition: Tests vs. Predictions

2019 ◽  
Author(s):  
Jing Yang ◽  
Luis San Andrés ◽  
Xueliang Lu
Keyword(s):  
Test Data ◽  
Mass Flow ◽  
Mass Fraction ◽  
Dynamic Stiffness ◽  
Dynamic Force ◽  
Rotor Speed ◽  
Force Coefficients ◽  
Supply Pressure ◽  
Liquid Mass ◽  
Wet Gas

Abstract High performance centrifugal compressors presently favor pocket damper seals (PDSs) as a choice of secondary flow control element offering a large effective damping coefficient to mitigate rotor sub synchronous whirl motions. Current and upcoming multiple-phase compression systems in subsea production facilities must demonstrate long term operation and continuous availability, free of harmful rotor instabilities. Plain annular seals and labyrinth seals are notoriously bad choices, whereas a PDS, by stopping the circulation of trapped liquid, operates stably. This paper presents experimental and computational fluid dynamics (CFD) results for the leakage and dynamic force coefficients obtained in a dedicated test facility hosting a fully partitioned PDS, four ribbed and with eight pockets per cavity. The test PDS, operating at a rotor speed 5,250 rpm (surface speed 35 m/s) and under a supply pressure/discharge pressure ratio up to 3.2, is supplied with a mixture of air and ISO VG 10 oil whose maximum liquid volume fraction (LVF) is 2.2%, equivalent to a liquid mass fraction of 84%. When supplied with just air (dry condition), the measured leakage increases nonlinearly with supply pressure. Under a wet gas condition, the recorded mass flow increases on account of the large difference in density between the liquid and the gas. CFD derived mass flow rates for both dry and wet gas conditions agree with the measured ones. The test dry gas PDS produces a direct dynamic stiffness (HR) increasing with frequency whereas the direct damping (C) and cross-coupled dynamic stiffness (hR) coefficients remain relatively constant. The CFD predicted damping agrees best with the test C albeit over predicting HR at low excitation frequencies and hR at all frequencies (< 175 Hz ∼ twice rotor speed). Under a wet gas condition with LVF = 0.4%, the test force coefficients show great variability over the excitation frequency range; in particular HR < 0, though growing with frequency due to the large liquid mass fraction. The CFD predictions, on the other hand, produce a dynamic direct stiffness HR > 0 for all frequencies. Both experimental hR and C for the wet gas PDS are larger than their counterparts for the dry gas seal. The CFD predicted C and hR, wet vs. dry, show a modest growth, yet remaining lower than the test data. The CFD derived flow field for a wet gas condition shows the seal radial partition walls (ridges) reduce the circumferential flow velocity and liquid accumulation within a pocket. Both the test data and CFD prediction show that the magnitude of the flexibility function for the PDS test system reduces when the two component mixture flows through the seal, hence revealing the additional effective damping, more pronounced for the test data rather than that from the predictions. Further work, experimental and CFD based, will continue to advance the technology of wet gas seals while bridging the gap between test data and computational physics model simulations.

On the Influence of Gas Content on the Rotordynamic Force Coefficients of a Three-Wave (Air in Oil) Annular Seal for Multiple Phase Pumps

2019 ◽  
Author(s):  
Luis San Andrés ◽  
Xueliang Lu ◽  
Tingcheng Wu
Keyword(s):  
Oil And Gas ◽  
Volume Fraction ◽  
Dynamic Stiffness ◽  
Excitation Frequency ◽  
Gas Content ◽  
Radial Clearance ◽  
Pure Liquid ◽  
Dynamic Force ◽  
Force Coefficients ◽  
Wet Gas

Abstract The subsea oil & gas industry efficiently uses multiphase pumps and wet gas compressors to eliminate upstream oil and gas separation stations, hence saving up to 30% in capital expenditures. Subsea multiphase process facilities must operate reliably for extended lengths of time while the wells, as they deplete, produce a process fluid varying from a pure liquid, to a mixture of gas and liquid, and to eventually just gas. The variation of gas volume fraction (GVF), by affecting the leakage and dynamic forced performance of sealing elements, alters turbomachinery performance to produce both an increase in synchronous speed rotor vibrations and a reduction in rotor dynamic stability. Prior laboratory work shows that plain cylindrical surface annular seals operating with a fluid flow in the laminar flow regime produce no direct (centering) stiffness and a large added mass, in particular for the liquid only condition. The early work also advanced a simple three-wave shape seal (akin to lobes) that generates a significant direct stiffness, impervious to GVF as large as 90%, and hence aids to increase the natural frequency of a vertical pump. Dynamic load tests for this wavy-seal configuration operating with a gas in liquid mixture [air in light ISO VG 10 oil] are the subject of this paper that presents dynamic force coefficients vs. excitation frequency (ω) while the shaft turns at a speed (Ω) equal to 3.5 krpm (23.3 m/s surface speed), a typical operating speed for multiphase pumps. The test seal has length L = 43 mm, diameter D = 127 mm, and a mean radial clearance cm = 0.191 mm. For operation with a pure liquid (GVF = 0), the seal force coefficients are frequency independent, thus a stiffness (K) - damping (C) − Mass (M) model fully characterizes the test article. On the other hand, for operation with an air in oil mixture, the test seal dynamic stiffness coefficients vary greatly with excitation frequency; the direct dynamic stiffness hardens while the cross coupled stiffness decreases as the frequency approaches running speed (ω &lt; Ω) and then increases for super synchronous frequency excitations (ω &gt; Ω). For operation with GVF from 0.1 to 0.8, the wavy seal produces a positive centering dynamic stiffness with large magnitude; a most desirable feature for a vertically installed pump. Notably, the seal direct damping coefficient (C) does not depend on the excitation frequency though reduces continuously as the inlet GVF increases from 0 to 1. For operation with either a pure liquid or a pure air conditions, a computational fluid dynamics (CFD) analysis accurately captures the seal leakage and force coefficients. The current research product adds relevant test data to better the design selection of seals in multiphase pumps.

Leakage and Dynamic Force Coefficients for Two Labyrinth Gas Seals: Teeth-on-Stator and Interlocking Teeth Configurations — A CFD Approach to Their Performance

2018 ◽  
Author(s):  
Luis San Andrés ◽  
Tingcheng Wu
Keyword(s):  
Pressure Ratio ◽  
Labyrinth Seal ◽  
Inlet Pressure ◽  
Dynamic Force ◽  
Rotor Speed ◽  
Frequency Range ◽  
Force Coefficients ◽  
Supply Pressure ◽  
Exit Pressure ◽  
Gas Seals

Labyrinth gas seals (LS) commonly used in turbomachines reduce secondary flow leakage. Conventional see-through labyrinth seal designs include either all Teeth-On-Stator (TOS) or all Teeth-On-Rotor (TOR). Experience shows that an interlocking labyrinth seal (ILS), with teeth on both stator and rotor, reduces gas leakage by up to 30% compared to the conventional see-through designs. However, field data for ILS rotordynamic characteristics is still vague and scarce in the literature. This work presents flow predictions for an ILS and a TOS LS, both seals share identical design features, namely radial clearance Cr = 0.2 mm, rotor diameter D = 150 mm, tooth pitch Li = 3.75 mm, and tooth height B = 3 mm. Air enters the seal at supply pressure Pin = 3.8, 6.9 bar (absolute) and temperature of 25 °C. The ratio of gas exit pressure to supply pressure ranges from 0.5 to 0.8, and the rotor speed is fixed at 10 krpm (surface speed of 79 m/s). The analysis implements a computational fluid dynamics (CFD) method with a multi-frequency-orbit rotor whirl model. The CFD predicted mass flow rate for the ILS is ∼21% lower than that of the TOS LS, thus making the ILS a more efficient choice. Integration of the dynamic pressure fields in the seal cavities, obtained for excitation frequency (ω) ranging from 12% to 168% of rotor speed (sub and super synchronous whirl), allows an accurate estimation of the seal dynamic force coefficients. For all the considered operating conditions, at low frequency range the TOS LS shows a negative direct stiffness (K < 0), frequency independent; whereas the ILS has K > 0 that increases with both frequency and supply pressure. For both seals, the magnitude of K decreases when the exit pressure/inlet pressure ratio increases. On the other hand, the cross-coupled stiffness (k) from both seals is frequency dependent, its magnitude increases with gas supply pressure, and the k for the ILS is more sensitive to a change in the exit/inlet pressure ratio. Notably, k turns negative for subsynchronous frequencies below rotor speed (Ω) for both the TOS LS and ILS. The direct damping (C) for the TOS LS remains constant for ω > ½ Ω and has a larger magnitude than the damping for the ILS over the frequency range up to 1.5Ω. An increase in exit/inlet pressure ratio decreases the direct damping for both seals. The effective damping coefficient, Ceff = (C-k/ω) whenever positive aids to damp vibrations, whereas Ceff < 0 is a potential source for an instability. For frequencies ω /Ω < 1.3, Ceff for the TOS LS is higher in magnitude than that for the ILS. From a rotordynamics point of view, the ILS is not a sound selection albeit it reduces leakage. Comparison of the CFD predicted force coefficients against those from a bulk flow model demonstrate the later simple model delivers poor results, often contradictory and largely indifferent to the type of seal, ILS or TOS LS. In addition, CFD model predictions are benchmarked against experimental dynamic force coefficients for two TOS LSs published by Ertas et al. (2012) and Vannini et al. (2014).

Leakage and Dynamic Force Coefficients for Two Labyrinth Gas Seals: Teeth-on-Stator and Interlocking Teeth Configurations. A Computational Fluid Dynamics Approach to Their Performance

2018 ◽  
Vol 141 (4) ◽  
Author(s):  
Tingcheng Wu ◽  
Luis San Andrés
Keyword(s):  
Gas Turbines ◽  
Pressure Ratio ◽  
Labyrinth Seal ◽  
Inlet Pressure ◽  
Dynamic Force ◽  
Rotor Speed ◽  
Frequency Range ◽  
Force Coefficients ◽  
Supply Pressure ◽  
Gas Seals

Labyrinth gas seals (LSs) commonly used in turbomachines reduce secondary flow leakage. Conventional see-through labyrinth seal designs include either all teeth-on-stator (TOS) or all teeth-on-rotor (TOR). Experience shows that an interlocking labyrinth seal (ILS), with teeth on both stator and rotor, reduces gas leakage by up to 30% compared to the conventional see-through designs. However, field data for ILS rotordynamic characteristics are still vague and scarce in the literature. This work presents flow predictions for an ILS and a TOS LS, both seals share identical design features, namely radial clearance Cr = 0.2 mm, rotor diameter D = 150 mm, tooth pitch Li = 3.75 mm, and tooth height B = 3 mm. Air enters the seal at supply pressure Pin = 3.8, 6.9 bar (absolute) and temperature of 25 °C. The ratio of gas exit pressure to supply pressure ranges from 0.5 to 0.8, and the rotor speed is fixed at 10 krpm (surface speed of 79 m/s). The analysis implements a computational fluid dynamics (CFD) method with a multi-frequency-orbit rotor whirl model. The CFD predicted mass flow rate for the ILS is ∼ 21% lower than that of the TOS LS, thus making the ILS a more efficient choice. Integration of the dynamic pressure fields in the seal cavities, obtained for excitation frequency (ω) ranging from 12% to 168% of rotor speed (sub and super synchronous whirl), allows an accurate estimation of the seal dynamic force coefficients. For all the considered operating conditions, at low frequency range, the TOS LS shows a negative direct stiffness (K < 0), frequency independent; whereas the ILS has K > 0 that increases with both frequency and supply pressure. For both seals, the magnitude of K decreases when the exit pressure/inlet pressure ratio increases. On the other hand, the cross-coupled stiffness (k) from both seals is frequency dependent, its magnitude increases with gas supply pressure, and k for the ILS is more sensitive to a change in the exit/inlet pressure ratio. Notably, k turns negative for subsynchronous frequencies below rotor speed (Ω) for both the TOS LS and the ILS. The direct damping (C) for the TOS LS remains constant for ω > ½ Ω and has a larger magnitude than the damping for the ILS over the frequency range up to 1.5 Ω. An increase in exit/inlet pressure ratio decreases the direct damping for both seals. The effective damping coefficient, Ceff = (C-k/ω), whenever positive aids to damp vibrations, whereas Ceff < 0 is a potential source for an instability. For frequencies ω/Ω < 1.3, Ceff for the TOS LS is higher in magnitude than that for the ILS. From a rotordynamics point of view, the ILS is not a sound selection albeit it reduces leakage. Comparison of the CFD predicted force coefficients against those from a bulk flow model demonstrates that the later simple model delivers poor results, often contradictory and largely indifferent to the type of seal, ILS or TOS LS. In addition, CFD model predictions are benchmarked against experimental dynamic force coefficients for two TOS LSs published by Ertas et al. (2012, “Rotordynamic Force Coefficients for Three Types of Annular Gas Seals With Inlet Preswirl and High Differential Pressure Ratio,” ASME J. Eng. Gas Turbines Power, 134(4), pp. 04250301–04250312) and Vannini et al. (2014, “Labyrinth Seal and Pocket Damper Seal High Pressure Rotordynamic Test Data,” ASME J. Eng. Gas Turbines Power, 136(2), pp. 022501–022509.)

On the Leakage, Torque, and Dynamic Force Coefficients of Air in Oil (Wet) Annular Seal: A Computational Fluid Dynamics Analysis Anchored to Test Data

2018 ◽  
Vol 141 (2) ◽  
Author(s):  
Luis San Andrés ◽  
Jing Yang ◽  
Xueliang Lu
Keyword(s):  
Test Data ◽  
Volume Fraction ◽  
Dynamic Stiffness ◽  
Pure Liquid ◽  
Dynamic Force ◽  
Liquid Content ◽  
Liquid Stream ◽  
Force Coefficients ◽  
Annular Seal ◽  
Gas Volume

Subsea pumps and compressors must withstand multiphase flows whose gas volume fraction (GVF) or liquid volume fraction (LVF) varies over a wide range. Gas or liquid content as a dispersed phase in the primary stream affects the leakage, drag torque, and dynamic forced performance of secondary flow components, namely seals, thus affecting the process efficiency and mechanical reliability of pumping/compressing systems, in particular during transient events with sudden changes in gas (or liquid) content. This paper, complementing a parallel experimental program, presents a computational fluid dynamics (CFD) analysis to predict the leakage, drag power, and dynamic force coefficients of a smooth surface, uniform clearance annular seal supplied with air in oil mixture whose inlet GVF varies discretely from 0.0 to 0.9, i.e., from a pure liquid stream to a nearly all-gas content mixture. The test seal has uniform radial clearance Cr = 0.203 mm, diameter D = 127 mm, and length L = 0.36 D. The tests were conducted with an inlet pressure/exit pressure ratio equal to 2.5 and a rotor surface speed of 23.3 m/s (3.5 krpm), similar to conditions in a pump neck wear ring seal. The CFD two-phase flow model, first to be anchored to test data, uses an Euler–Euler formulation and delivers information on the precise evolution of the GVF and the gas and liquid streams' velocity fields. Recreating the test data, the CFD seal mass leakage and drag power decrease steadily as the GVF increases. A multiple-frequency shaft whirl orbit method aids in the calculation of seal reaction force components, and from which dynamic force coefficients, frequency-dependent, follow. For operation with a pure liquid, the CFD results and test data produce a constant cross-coupled stiffness, damping, and added mass coefficients, while also verifying predictive formulas typical of a laminar flow. The injection of air in the oil stream, small or large in gas volume, immediately produces force coefficients that are frequency-dependent; in particular the direct dynamic stiffness which hardens with excitation frequency. The effect is most remarkable for small GVFs, as low as 0.2. The seal test direct damping and cross-coupled dynamic stiffness continuously drop with an increase in GVF. CFD predictions, along with results from a bulk-flow model (BFM), reproduce the test force coefficients with great fidelity. Incidentally, early engineering practice points out to air injection as a remedy to cure persistent (self-excited) vibration problems in vertical pumps, submersible and large size hydraulic. Presently, the model predictions, supported by the test data, demonstrate that even a small content of gas in the liquid stream significantly raises the seal direct stiffness, thus displacing the system critical speed away to safety. The sound speed of a gas in liquid mixture is a small fraction of those speeds for either the pure oil or the gas, hence amplifying the fluid compressibility that produces the stiffness hardening. The CFD model and a dedicated test rig, predictions and test data complementing each other, enable engineered seals for extreme applications.

On the Leakage, Torque and Dynamic Force Coefficients of an Air in Oil (Wet) Annular Seal: A CFD Analysis Anchored to Test Data

2018 ◽  
Author(s):  
Luis San Andrés ◽  
Jing Yang ◽  
Xueliang Lu
Keyword(s):  
Test Data ◽  
Volume Fraction ◽  
Dynamic Stiffness ◽  
Pure Liquid ◽  
Dynamic Force ◽  
Liquid Content ◽  
Liquid Stream ◽  
Force Coefficients ◽  
Annular Seal ◽  
Gas Volume

Subsea pumps and compressors must withstand multi-phase flows whose gas volume fraction (GVF) or liquid volume fraction (LVF) varies over a wide range. Gas or liquid content as a dispersed phase in the primary stream affects the leakage, drag torque, and dynamic forced performance of secondary flow components, namely seals, thus affecting the process efficiency and mechanical reliability of pumping/compressing systems, in particular during transient events with sudden changes in gas (or liquid) content. This paper, complementing a parallel experimental program, presents a computational fluid dynamics (CFD) analysis to predict the leakage, drag power and dynamic force coefficients of a smooth surface, uniform clearance annular seal supplied with an air in oil mixture whose inlet GVF varies discretely from 0.0 to 0.9, i.e., from a pure liquid stream to a nearly all gas content mixture. The test seal has uniform radial clearance Cr = 0.203 mm, diameter D = 127 mm, and length L = 0.36 D. The tests were conducted with an inlet pressure/exit pressure ratio equal to 2.5 and a rotor surface speed of 23.3 m/s (3.5 krpm), similar to conditions in a pump neck wear ring seal. The CFD two-phase flow model, first to be anchored to test data, uses an Euler-Euler formulation and delivers information on the precise evolution of the GVF and the gas and liquid streams’ velocity fields. Recreating the test data, the CFD seal mass leakage and drag power decrease steadily as the GVF increases. A multiple-frequency shaft whirl orbit method aids in the calculation of seal reaction force components, and from which dynamic force coefficients, frequency dependent, follow. For operation with a pure liquid, the CFD results and test data produce a constant cross-coupled stiffness, damping, and added mass coefficients, while also verifying predictive formulas typical of a laminar flow. The injection of air in the oil stream, small or large in gas volume, immediately produces force coefficients that are frequency dependent; in particular the direct dynamic stiffness which hardens with excitation frequency. The effect is most remarkable for small GVFs, as low as 0.2. The seal test direct damping and cross-coupled dynamic stiffness continuously drop with an increase in GVF. CFD predictions, along with results from a bulk-flow model (BFM), reproduce the test force coefficients with great fidelity. Incidentally, early engineering practice points out to air injection as a remedy to cure persistent (self-excited) vibration problems in vertical pumps, submersible and large size hydraulic. Presently, the model predictions, supported by the test data, demonstrate that even a small content of gas in the liquid stream significantly raises the seal direct stiffness, thus displacing the system critical speed away to safety. The sound speed of a gas in liquid mixture is a small fraction of those speeds for either the pure oil or the gas, hence amplifying the fluid compressibility that produces the stiffness hardening. The CFD model and a dedicated test rig, predictions and test data complementing each other, enable engineered seals for extreme applications.

A NONHOMOGENEOUS BULK FLOW MODEL FOR GAS IN LIQUID FLOW ANNULAR SEALS: AN EFFORT TO PRODUCE ENGINEERING RESULTS

2021 ◽  
pp. 1-31
Author(s):  
Xueliang Lu ◽  
Luis San Andres ◽  
Jing Yang
Keyword(s):  
Pressure Drop ◽  
Test Data ◽  
Liquid Flow ◽  
Flow Model ◽  
Bulk Flow ◽  
Experimental Results ◽  
Pure Liquid ◽  
Dynamic Force ◽  
Force Coefficients ◽  
Direct Stiffness

Abstract Seals in multiple phase rotordynamic pumps must operate without compromising system efficiency and stability. Both field operation and laboratory experiments show that seals supplied with a gas in liquid mixture (bubbly flow) can produce rotordynamic instability and excessive rotor vibrations. This paper advances a nonhomogeneous bulk flow model (NHBFM) for the prediction of the leakage and dynamic force coefficients of uniform clearance annular seals lubricated with gas in liquid mixtures. Compared to a homogeneous BFM (HBFM), the current model includes diffusion coefficients in the momentum transport equations and a field equation for the transport of the gas volume fraction (GVF). Published experimental leakage and dynamic force coefficients for two seals supplied with an air in oil mixture whose GVF varies from 0 (pure liquid) to 20% serve to validate the novel model as well as to benchmark it against predictions from a HBFM. The first seal withstands a large pressure drop (~ 38 bar) and the shaft speed equals 7.5 krpm. The second seal restricts a small pressure drop (1.6 bar) as the shaft turns at 3.5 krpm. The first seal is typical as a balance piston whereas the second seal is found as a neck-ring seal in an impeller. For the high pressure seal and inlet GVF = 0.1, the flow is mostly homogeneous as the maximum diffusion velocity at the seal exit plane is just ~0.1% of the liquid flow velocity. Thus, both the NHBFM and HBFM predict similar flow fields, leakage (mass flow rate) and drag torque. The difference between the predicted leakage and measurement is less than 5%. The NHBFM direct stiffness (K) agrees with the experimental results and reduces faster with inlet GVF than the HBFM K. Both direct damping (C) and cross-coupled stiffness (k) increase with inlet GVF &lt; 0.1.Compared to the test data, the two models generally under predict C and k by ~ 25%. Both models deliver a whirl frequency ratio (fw) ~ 0.3 for the pure liquid seal, hence closely matching the test data. fw raises to ~0.35 as the GVF approaches 0.1. For the low pressure seal the flow is laminar, the experimental results and both NHBFM and HBFM predict a null direct stiffness (K). At an inlet GVF = 0.2, the NHBFM predicted added mass (M) is ~30 % below the experimental result while the HBFM predicts a null M. C and k predicted by both models are within the uncertainty of the experimental results. For operation with either a pure liquid or a mixture (GVF = 0.2), both models deliver fw = 0.5 and equal to the experimental finding. The comparisons of predictions against experimental data demonstrate the NHBFM offers a marked improvement, in particular for the direct stiffness (K). The predictions reveal the fluid flow maintains the homogeneous character known at the inlet condition.

Flow Characteristics of Fluid Droplet Obtained From Air Assisted Atomizer

2011 ◽  
Author(s):  
Pipatpong Watanawanyoo ◽  
Hirofumi Mochida ◽  
Hiroyuki Hirahara ◽  
Sumpun Chaitep
Keyword(s):  
Mass Flow ◽  
Cone Angle ◽  
Flow Ratio ◽  
Test Liquid ◽  
Solid Cone ◽  
Spray Cone ◽  
Supply Pressure ◽  
Liquid Mass ◽  
Air Supply ◽  
Mass Flow Ratio

Air assisted atomizer system was designed and developed for fuel injection. The present purpose is to utilize a low pressure in supplying of atomized fuel. Distilled water was used as test liquid on the experiments for the system of atomization. The results revealed air assisted atomizer had a capability to inject the test liquid in the range of the rates of 0.0019–0.00426 kg/s, with the use of air pressure supplied from 68.9 to 689 kPa. In this research, the test liquid supply pressure was kept constant and the air flow rate through the atomizer was varied over a range of air supply pressure to obtain the variation in air liquid mass flow ratio (ALR). The spray solidity was studied by taking pictures of the spray at different liquid air supply pressures. The experimental investigations suggest that spray cone angle tends to increase with increasing in air liquid mass flow ratio because the kinetic energy of the flow keeps on increasing. The solid cone spray has a pattern of penetration depth between 408–446 mm. and cone angle between 14.5–23.6°. It was observed that spray formed the solid cone at all the operating conditions.

Leakage and Force Coefficients of a Grooved Wet (Bubbly Liquid) Seal for Multiphase Pumps and Comparisons With Prior Test Results for a Three Wave Seal

2019 ◽  
Vol 142 (1) ◽  
Author(s):  
Xueliang Lu ◽  
Luis San Andrés ◽  
Tingcheng Wu
Keyword(s):  
Pressure Drop ◽  
Volume Fraction ◽  
Dynamic Stiffness ◽  
Pressure Ratio ◽  
Excitation Frequency ◽  
Gas Content ◽  
Bubbly Liquid ◽  
Dynamic Force ◽  
Force Coefficients ◽  
Ring Seal

Abstract In the subsea oil and gas industry, multiphase pumps and wet gas compressors are engineered choices saving transportation and separation facility costs. In these machines, seals handling multiple phase components must be able to operate without affecting the system efficiency and its dynamic stability. This paper, extending prior work conducted with uniform clearance and wavy surface annular seals, presents measurements of leakage and dynamic force coefficients in a grooved seal whose dimensions are scaled from an impeller wear ring seal in a boiler feed pump. The 14-grooves seal has diameter D = 127 mm, length L = 0.34 D, and clearance c = 0.211 mm; each groove has shallow depth dg ∼2.6 c and length Lg ∼ 3.4% L. At a shaft speed of 3.5 krpm (surface speed = 23.3 m/s), a mixture of air in ISO VG 10 oil with inlet gas volume fraction (GVF) ranging from 0 (just oil) to 0.7 (mostly air) lubricates the seal. The pressure ratio (inlet/exit) is 2.9. The flow is laminar since the liquid is viscous and the pressure drop is low. The measured mixture mass flow decreases continuously with an increase in inlet GVF. The seal stiffnesses (direct K and cross coupled k), added mass (M), and direct damping (C) coefficients are constant when the supplied mixture is low in gas content, GVF ≤ 0.1. As the gas content increases, 0.2 ≤  GVF ≤ 0.5, the seal direct dynamic stiffness becomes nil with an increase in excitation frequency, whereas k and C reduce steadily with GVF. In general, for GVF ≤ 0.5, the direct damping is invariant with frequency; variations appearing for GVF = 0.7. Compared against a three wave annular seal, the grooved seal offers much lower force coefficients, in particular the viscous damping. Thus, for laminar flow operation (heavy oil) with a low pressure drop as in a wear ring seal, a three wave seal is recommended as it also offers a significant centering stiffness.

Leakage and Force Coefficients of a Grooved Wet (Bubbly Liquid) Seal for Multiphase Pumps and Comparisons With Prior Test Results for a Three Wave Seal

2019 ◽  
Author(s):  
Xueliang Lu ◽  
Luis San Andrés ◽  
Tingcheng Wu
Keyword(s):  
Pressure Drop ◽  
Volume Fraction ◽  
Dynamic Stiffness ◽  
Pressure Ratio ◽  
Excitation Frequency ◽  
Gas Content ◽  
Bubbly Liquid ◽  
Dynamic Force ◽  
Force Coefficients ◽  
Ring Seal

Abstract In the subsea oil and gas industry, multiphase pumps and wet gas compressors are engineered choices saving transportation and separation facility costs. In these machines, seals handling multiple phase components must be able to operate without affecting the system efficiency and its dynamic stability. This paper, extending prior work conducted with uniform clearance and wavy surface annular seals, presents measurements of leakage and dynamic force coefficients in a grooved seal whose dimensions are scaled from an impeller wear ring seal in a boiler feed pump. The 14-grooves seal has diameter D = 127 mm, length L = 0.34 D, and clearance c = 0.211 mm; each groove has shallow depth dg ∼2.6 c and length Lg ∼ 3.4% L. At a shaft speed of 3.5 krpm (surface speed = 23.3 m/s), a mixture of air in ISO VG 10 oil with inlet gas volume fraction (GVF) ranging from 0 (just oil) to 0.7 (mostly air) lubricates the seal. The pressure ratio (inlet/exit) is 2.9. The flow is laminar since the liquid is viscous and the pressure drop is low. The measured mixture mass flow decreases continuously with an increase in inlet GVF. The seal stiffnesses (direct K and cross coupled k), added mass (M), and direct damping (C) coefficients are constant when the supplied mixture is low in gas content, GVF ≤ 0.1. As the gas content increases, 0.2 ≤ GVF ≤ 0.5, the seal direct dynamic stiffness becomes nil with an increase in excitation frequency, whereas k and C reduce steadily with GVF. In general, for GVF ≤ 0.5 the direct damping is invariant with frequency; variations appearing for GVF = 0.7. Compared against a three wave annular seal, the grooved seal offers much lower force coefficients, in particular the viscous damping. Thus, for laminar flow operation (heavy oil) with a low pressure drop as in a wear ring seal, a three wave seal is recommended as it also offers a significant centering stiffness.

Sign in / Sign up

Export Citation Format

Share Document