Predictions for Non-Contacting Mechanical Face Seal Vibration With External Excitation From Pump Vibration: Part II — Flexibly Mounted Rotor

2018 ◽  
Author(s):  
Clay S. Norrbin ◽  
Dara W. Childs
Keyword(s):  
Excitation Frequency ◽  
Harmonic Excitation ◽  
Fluid Film ◽  
Axial Distance ◽  
Mechanical Seal ◽  
Seal Ring ◽  
Mechanical Seals ◽  
Running Speed ◽  
Frequency Dependent ◽  
Frequency Independent

Stability and response predictions are presented for a Flexibly Mounted Rotor (FMR) mechanical seal ring using the model developed by Childs in 2018. The seal ring is excited by lateral/pitch vibration from the rotor/housing. The model includes a frequency dependent stiffness and damping model for the O-ring and a frequency independent model for the fluid film. The dynamic coefficients are speed and frequency dependent. The mechanical seal is modeled after a typical FMR mechanical seal. Parameters for radius, fluid film clearance, and O-Ring axial distances are varied. The axial distance between the O-Ring and seal ring inertia center doz is found to couple lateral rotor motion and seal ring pitch vibration. The predictions show a dependency on both excitation frequency and running speed. The analyzed FMR has a critical region with high transmissibility in a region around a speed and excitation frequency of 70 kRPM. Another region of high transmissibility is predicted to be with sub-harmonic excitation frequency. The FMR seal ring also has an unstable region that is sub-harmonic of 1% running speed. Running back on the HQ curve for a pump causes broadband sub-harmonic excitaiton, which can cause rub failures for FMR mechanical seals.

Predictions for Non-Contacting Mechanical Face Seal Vibration With External Excitation From Pump Vibration: Part I — Flexibly Mounted Stator

2018 ◽  
Author(s):  
Clay S. Norrbin ◽  
Dara W. Childs
Keyword(s):  
Excitation Frequency ◽  
Mechanical Seal ◽  
Seal Ring ◽  
External Excitation ◽  
Frequency Dependent ◽  
Frequency Independent ◽  
Mechanical Face Seal ◽  
Stiffness And Damping ◽  
Damping Model ◽  
Independent Model

Stability and response predictions are presented for a Flexibly Mounted Stator (FMS) mechanical seal ring using the model developed by Childs in 2018. The seal ring is excited by external vibration from the rotor/housing. The model includes a frequency dependent stiffness and damping model for the O-ring and a frequency independent model for the fluid film. The dynamic coefficients depend on both speed and excitation frequency. Data used in defining the model are representative of a typical FMS mechanical seal. Parameters for radius and O-Ring placement are varied. The predictions show an insignificant dependency on speed. The predictions are strongly frequency dependent with a critical speed of 90 kRPM. The FMS is predicted to be stable to frequencies below 140 kRPM. The distance between the O-Ring and seal ring inertia center doz couples lateral and pitch-yaw motion of the seal ring. Overall, if doz is kept small, the seal ring is predicted to not have any stability or response issues.

A Study on the Leakage and Rotordynamic Performance of a Long Labyrinth Seal Under Mainly Air Conditions

2019 ◽  
Vol 141 (12) ◽  
Author(s):  
Min Zhang ◽  
Dara W. Childs
Keyword(s):  
Silicone Oil ◽  
Dynamic Stiffness ◽  
Excitation Frequency ◽  
Labyrinth Seal ◽  
System Stability ◽  
Test Fluid ◽  
Liquid Volume ◽  
Frequency Dependent ◽  
Frequency Independent ◽  
The Impact

Abstract This paper investigates the impact of liquid presence in air on the leakage and rotordynamic coefficients of a long (length-to-diameter ratio L/D = 0.747) teeth-on-stator labyrinth seal. The test fluid is a mixture of air and silicone oil (PSF-5cSt). Tests are carried out at inlet pressure Pi = 62.1 bars, three pressure ratios from 0.21 to 0.46, three speeds from 10 to 20 krpm, and six inlet liquid volume fractions (LVFs) from 0% to 15%. Complex dynamic-stiffness coefficients Hij are measured. The real parts of Hij are too frequency dependent to be fitted by frequency-independent stiffness and virtual-mass coefficients. Therefore, this paper presents frequency-dependent direct stiffness KΩ and cross-coupled stiffness kΩ. The imaginary parts of Hij produce frequency-independent direct damping C. Test results show that, under both pure- and mainly air conditions, the leakage mass flowrate m˙ of the test seal steadily increases as inlet LVF increases. KΩ is negative under all test conditions, and the magnitude of KΩ increases as inlet LVF increases, leading to a larger negative centering force on the associated compressor rotor. Under pure-air conditions, kΩ is a small negative value. Injecting oil into the air increases kΩ slightly and make the magnitude of kΩ closer to zero. Under mainly air conditions, increasing inlet LVF from 2% to 15% has little impact on kΩ. C normally increases as inlet LVF increases. The value of the effective damping Ceff = C − kΩ/Ω near 0.5ω is of significant interest to the system stability since an unstable centrifugal compressor may precess at approximately 0.5ω. Ω denotes the excitation frequency. The oil presence in the air has little impact on the value of Ceff near 0.5ω. Also, the liquid presence does not change the insensitiveness of m˙, KΩ, kΩ, C, and Ceff to change in ω; i.e., under both pure- and mainly air conditions, changes in ω has little impact on m˙, KΩ, kΩ, C, and Ceff.

Analysis of Carrying Capacity and Friction Torque of Friction Pair Fluid-Film for High Parameter Bellows Mechanical Seal

2013 ◽  
Vol 455 ◽  
pp. 207-211
Author(s):  
Mutellip Ahmat ◽  
Zhi Wei Niu ◽  
Guzaiayi Abudoumijiti
Keyword(s):  
Carrying Capacity ◽  
High Speed ◽  
Influence Factor ◽  
Friction Pair ◽  
Scientific Basis ◽  
Friction Torque ◽  
Fluid Film ◽  
Mechanical Seal ◽  
Mechanical Seals ◽  
The Relationship

The friction pair for bellows mechanical seal as a friction element is one of the key components for it. In this research, by based on the computational fluid dynamics (CFD) numerical theory, using the Fluent software, corresponding model and parameters, the fluid-film between the clearance of the sealing ring friction pair for the bellows mechanical seal under such the high-temperature, high-pressure, high-speed as complex working conditions is numerically simulated, the relationship between the carrying-capacity of the fluid-film and the temperature, the viscosity of the fluid-film, the relationship between friction torque of the fluid-film and the speed, viscosity of the fluid-film, the influence factor of leakage are obtained. The researching results provide the scientific basis for the optimization designing of the high parameter bellows mechanical seals.

Optimum Design of Flat End Face Mechanical Seal Based on Coupling Analysis

2010 ◽  
Vol 37-38 ◽  
pp. 819-822 ◽  
Author(s):  
Jian Feng Zhou ◽  
Bo Qin Gu ◽  
Chun Lei Shao
Keyword(s):  
Optimum Design ◽  
Thermal Deformation ◽  
Coupling Effect ◽  
Design Method ◽  
Fluid Film ◽  
Outer Side ◽  
Mechanical Seal ◽  
Mechanical Seals ◽  
Friction Heat ◽  
Bearing Force

The flat end face mechanical seals are widely used in shaft sealing at moderate rotational speed. The thermal deformation of the rotating and stationary rings initiated by friction heat of fluid film should be primarily considered in the design of mechanical seal. In consideration of the coupling effect among the thermal deformation of sealing rings, the fluid flow in the gap composed by end faces of sealing rings and the heat transfer from fluid film to sealing rings, the optimum design method for flat end face mechanical seal is established. The end faces are fabricated to form a divergent gap at the inner side of the sealing rings, and a convergent gap will occur at the outer side and a parallel gap will be obtained at where the original divergent gap is due to the thermal deformation. After optimization, the leakage rate can be reduced while the bearing force of fluid film is still large enough to keep the fluid lubrication of the end faces.

scholarly journals Research on the Dynamic Characteristics of Mechanical Seal under Different Extrusion Fault Degrees

Processes ◽  
2020 ◽  
Vol 8 (9) ◽  
pp. 1057
Author(s):  
Yin Luo ◽  
Yakun Fan ◽  
Yuejiang Han ◽  
Weqi Zhang ◽  
Emmanuel Acheaw
Keyword(s):  
Film Thickness ◽  
Dynamic Characteristics ◽  
Fluid Film ◽  
Mechanical Seal ◽  
Mechanical Seals ◽  
Rotating Speed ◽  
Analysis Process ◽  
Fluid Film Thickness ◽  
Object Of Study ◽  
Fault Mechanism

In order to explore the dynamic characteristics of the mechanical seal under different fault degrees, this paper selected the upstream pumping mechanical seal as the object of study. The research established the rotating ring-fluid film-stationary ring 3D model, which was built to analyze the fault mechanism. To study extrusion fault mechanism and characteristics, different dynamic parameters were used in the analysis process. Theoretical analysis, numerical simulation, and comparison were conducted to study the relationship between the fault degree and dynamic characteristics. It is the first time to research the dynamic characteristics of mechanical seals in the specific extrusion fault. This paper proved feasibility and effectiveness of the new analysis method. The fluid film thickness and dynamic characteristics could reflect the degree of the extrusion fault. Results show that the fluid film pressure fluctuation tends to be more intensive under the serious extrusion fault condition. The extrusion fault is more likely to occur when the fluid film thickness is too large or too small. Results illustrate the opening force is affected with the fluid film lubrication status and seal extrusion fault degrees. The fluid film stiffness would not always increase with the rotating speed growth. The seal fault would occur with the increasing of rotating speeds, and the leakage growth fluctuations could reflect the fault degree.

Relationship Between Vibrations and Mechanical Seal Failures in Centrifugal Pumps

2005 ◽  
Author(s):  
David B. Stefanko ◽  
Robert A. Leishear
Keyword(s):  
Industrial Applications ◽  
The Other ◽  
Fluid Film ◽  
Operating Speed ◽  
Mechanical Seal ◽  
Mechanical Seals ◽  
Centrifugal Pumps ◽  
Radial Vibrations ◽  
The Common ◽  
Bearing Design

A reduction of radial vibrations in mechanical seals increases the life of the seals in centrifugal pumps. Mechanical seals consist of two smooth seal faces. One face is stationary with respect to the pump. The other rotates. Between the faces a fluid film evaporates as the fluid moves radially. Ideally, the film evaporates as it reaches the outer surface of the seal faces, thereby preventing leakage from the pump and effectively lubricating the two surfaces. Relative vibrations between the two surfaces affect the fluid film, damage the faces, and decrease the life of the seals. In a series of industrial applications, different techniques were used to minimize vibration, and the life of the seals was shown to significantly increase. The operating speed was controlled in one case, the bearing design was replaced in another case, and the stiffness of the pump was altered in still another case. The common corrective action in each case was a reduction in vibration.

A Novel Controlled-Motion Test Rig to Evaluate Effect of Synchronous and Subsynchronous Lateral Vibration on Reliability and Performance of Mechanical Seals in Pumps

2020 ◽  
Author(s):  
Clay S. Norrbin ◽  
Adolfo Delgado
Keyword(s):  
Mineral Oil ◽  
Mechanical Seal ◽  
Mechanical Seals ◽  
Test Rig ◽  
Flow Loop ◽  
Rotating Shaft ◽  
Premature Failure ◽  
Frequency Independent ◽  
Controlled Motion ◽  
And Performance

Abstract Mechanical seals are commonly used in rotating machinery to contain liquid leakage past a rotating shaft. Pumps vibration often exhibit both synchronous and sub-synchronous whirling, which may lead to premature failure of mechanical seals. A test rig was developed to simulate a running pump environment for the mechanical seal. The controlled-motion test rig comprises a flexibly-mounted-rotor connected to a pair of electrohydraulic shakers. This configuration allows imposing whirl orbits to a flexibly-mounted-rotor (FMR) mechanical seal at any prescribed frequency independent of rotor speed. A 6-axis load cell provides direct measurements of the reaction forces at the mechanical seal stationary component. Five Eddy current sensors and capacity probes track the 5 DOFs of the mechanical seal dynamic face. The flow loop is a modified plan 54 with an external pump capable of delivering 32 lpm at 14 bar using VG 2 mineral oil, and an external heat exchanger to regulate oil temperature. Tests were performed on a 3-inch (76.2 mm) FMR seal. Input rotor whirl vibration was increased to 10 mils pk-pk (254 microns), while cooling flow (VG2 mineral oil) was set to 8 lpm and pressure was varied from 1.7–6.9 lpm. The measurements include steady state values of temperature, power loss, clearance and leakage; and dynamic measurements of seal face wobble, wobble-imposed torque, relative lateral movement and fluid film shear.

scholarly journals Relationship Between Vibrations and Mechanical Seal Life in Centrifugal Pumps

2007 ◽  
Author(s):  
Robert A. Leishear ◽  
David B. Stefanko
Keyword(s):  
Crack Growth ◽  
Fatigue Damage ◽  
The Other ◽  
Fluid Film ◽  
Time To Failure ◽  
Mechanical Seal ◽  
Mechanical Seals ◽  
Centrifugal Pumps ◽  
Vibration Data ◽  
Cyclic Stresses

A reduction of vibrations in mechanical seals increases the life of the seals in centrifugal pumps by minimizing fatigue damage. Mechanical seals consist of two smooth seal faces. One face is stationary with respect to the pump. The other rotates. Between the faces a fluid film evaporates as the fluid moves radially outward across the seal face. Ideally, the film evaporates as it reaches the outer surface of the seal faces, thereby preventing leakage from the pump and effectively lubricating the two surfaces. Relative vibrations between the two surfaces affect the fluid film and lead to stresses on the seal faces, which lead to fatigue damage. As the fluid film breaks down, impacts between the two seal faces create tensile stresses on the faces, which cycle at the speed of the motor rotation. These cyclic stresses provide the mechanism leading to fatigue crack growth. The magnitude of the stress is directly related to the rate of crack growth and time to failure of a seal. Related to the stress magnitude, vibration data is related to the life of mechanical seals in pumps.

Coupling Analysis of Fluid Film and Thermal Deformation of Sealing Members in Spiral Groove Mechanical Seal

2007 ◽  
Vol 353-358 ◽  
pp. 2455-2458
Author(s):  
Jian Feng Zhou ◽  
Bo Qin Gu
Keyword(s):  
Thermal Deformation ◽  
Critical Speed ◽  
Fluid Film ◽  
Hydrodynamic Effect ◽  
Mechanical Seal ◽  
Mechanical Seals ◽  
Spiral Groove ◽  
Coupling Analysis ◽  
Rotating Speed ◽  
Bearing Force

The thermo-hydrodynamic effect in the spiral groove mechanical seal was investigated. The coupling analysis of the fluid film and the thermal deformation of sealing rings was carried out, the separation angle obtained, and the shape of the gap between the two deformed end faces determined. The results indicate that the increase of the temperature of the fluid film and the thermal deformation of the sealing rings cause the increase of the leakage rate. There exists a critical rotating speed, when the rotating speed is lower than the critical speed, the bearing force increases with the increase of the rotating speed, and once the rotating speed is higher than the critical speed, the bearing force decreases reversely. The thermal deformation weakens the hydrodynamic effect of the spiral groove mechanical seals.

Vibration Modeling and Experimental Results of Two Phase Flow Twin-Screw Pump

2015 ◽  
Author(s):  
Ameen R. A. Muhammed ◽  
Dara W. Childs
Keyword(s):  
Critical Speed ◽  
Dynamic Pressure ◽  
Excitation Frequency ◽  
Harmonic Excitation ◽  
Running Speed ◽  
Two Phase ◽  
Screw Pump ◽  
Positive Displacement ◽  
Twin Screw ◽  
Dynamic Pressure Measurements

In turbomachines, the transfer of energy between the rotor and the fluid does not — in theory — result in lateral forces on the rotor. In positive displacement machines, on the other hand, the transfer of energy between the moving and stationary components usually results in unbalanced pressure fields and forces. In [1] the authors developed a model to predict the dynamic forces in twin screw pumps, showing that the helical screw shape generates hydraulic forces that oscillate at multiples of running speed. The work presented here attempts to validate the model in [1] using a clear-casing twin screw pump. The pump runs in both single and multiphase conditions with exit pressure up to 300 KPa and a flow rate 0.6 liter per second. The pump was instrumented with dynamic pressure probes across the axial length of the screw in two perpendicular directions to validate the dynamic model. Two proximity probes measured the dynamic rotor displacement at the outlet to validate the rotordynamics model and the hydrodynamic cyclic forces predicted in [1]. The predictions were found in good agreement with the measurements. The amplitude of the dynamic pressure measurements in two perpendicular plans supported the main assumptions of the model (constant pressure inside the chambers and linear pressure drop across the screw lands). The predicted rotor orbits at the pump outlet in the middle of the rotor matched the experimental orbits closely. The spectrum of the response showed harmonics of the running speed as predicted by the model. The pump rotor’s calculated critical speed was at 24.8 krpm, roughly 14 times the rotor’s running speed of 1750 rpm. The measured and observed excitation frequencies extended out to nine times running speed, still well below the 1st critical speed. However, for longer twin-screw pumps running at higher speed, the coincidence of a higher-harmonic excitation frequency with the lightly damped 1st critical speed should be considered.

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