Step Clearance Seals: An Analysis to Demonstrate Their Unique Performance

Lu, Xueliang; Andrés, Luis San

doi:10.1115/1.4041719

Cited by 3 publications

References 7 publications

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

Andrés

2020

Journal of Fluids Engineering

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Subsea multiphase pumps must operate reliably with a process fluid transitioning from a pure liquid, to a mixture of gas and liquid, and to eventually just gas; and pressure seals controlling secondary leakage paths are important for both pump efficiency and dynamic stability considerations, in particular, for flows with a sizable gas volume fraction (GVF). Early work advances a three-wave shape seal that generates significant direct stiffness and hence aids to increase the natural frequency of a vertical pump. This paper details dynamic load tests and produces rotordynamic force coefficients for the wavy-seal operating with a gas in liquid mixture made of air in light ISO VG 10 oil. For operation with pure liquid, GVF = 0, a stiffness (K), damping (C), and added mass (M) model fully characterizes the test article. For operation with a mixture, the seal dynamic stiffness coefficients vary greatly with excitation frequency; the direct dynamic stiffness hardens while the cross coupled stiffness decreases as the whirl frequency approaches shaft speed and then increases for super synchronous frequency. For operation with GVF from 0.1 to 0.8, the seal produces a large positive centering dynamic stiffness. Notably, the seal direct damping coefficient does not depend on frequency though reduces continuously as the inlet GVF increases from 0 to 1 (all gas). The current research adds relevant test data and unique dynamic force coefficients to the design selection of seals in multiphase pumps.

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

Andrés

2020

Journal of Fluids Engineering

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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

Andrés

2019

Volume 7B: Structures and Dynamics

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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.

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Mechanism analysis of double helical balance drum to improve axial force of multistage pump

Chen

Lihuan

Peng³

et al. 2022

Mod. Phys. Lett. B

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In the case of high pressure, the size of the multistage pump axial force sometimes reaches hundreds of tons, the seriousness of the problem generated by excessive axial force has surpassed the efficiency, wear and other factors, and has become a decisive factor in the stable operation of multistage pumps. In this paper, the 11-stage double-case multistage pump is taken as the research object. On the basis of studying the clearance internal flow mechanism, according to the pressure difference equation of axial motion of clearance fluid, the main factors affecting the balance force of the balance drum are analyzed, and a new type of balance drum — “double helical balance drum” is proposed, which is compared with the smooth balance drum in the hydraulic performance and axial force performance. The research shows that with the increase of the axial displacement of the balance clearance, the pressure drop between the clearances decreases linearly. Compared with the smooth balance drum, the pressure drop at the inlet and outlet of the helical balance drum is 1.30 times that of the smooth balance drum under the design flow rate condition, the mean velocity, mean velocity curl and velocity coefficient of the double helical balance drum increase, indicating that adding double helix can increase the dynamic pressure ratio of clearance fluid. In addition, the test results show that the head and efficiency of the double helical balance drum of multistage pump is increased by 0.76% and 1.1%, respectively, compared with the smooth balance drum, and the vibration amplitude of the front and rear bearing is reduced by 3.36%, 0.76% and 1.75% on average along the axial, radial and tangential direction. In addition, the temperature of the front and rear bearing is reduced by 3.1% and 8.7%, respectively, indicating that the double helical balance drum can effectively improve the hydraulic performance and axial force performance of the multistage pump at design operating point. The results of the study can provide reference for the long-cycle stable operation of multistage pumps and the optimization of balance drum design.

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Step Clearance Seals: An Analysis to Demonstrate Their Unique Performance

Cited by 3 publications

References 7 publications

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

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

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

Mechanism analysis of double helical balance drum to improve axial force of multistage pump

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