Static Seal Research Articles

Influence of the axial tooth structure on the pressure resistance of the magnetic fluid sealing device

Magnetic fluid sealing is one of the most advanced applications of magnetic fluids. Presently, the research field mainly focuses on the polar teeth, leaving a gap in the structure of the shaft. To effectively achieve the improvement of the compression resistance of the magnetic fluid sealing device, an improvement of the axial structure is required. From this perspective, this study presents a novel shaft axis gear structure for the establishment of a magnetic fluid static seal compression capacity for this model. The shaft is studied through the simulation analysis of the tooth height, the width and eccentric distance was investigated for the influence of the compression capacity. An experimental device was then used to validate the results and confirm the validity of the findings.

Effect of pressure fluctuation in oil-gas multiphase pump on cavitation and performance of sealing liquid film

During the operation of the oil-gas multiphase pump, due to the variable gas content of the incoming flow, the medium pressure at the high-pressure end fluctuates widely, which is easy to cause the stress change at both ends of the mechanical seal compensation ring and “instability” phenomenon. In this paper, a three-dimensional spiral groove seal film model is established. Considering the cavitation effect of liquid film gap, the variation law of end face cavitation and sealing performance of liquid film seal is explored according to the effect of pressure pulsation in the pump on the inner diameter side (Static mechanical seal, PLAN74 flushing scheme in API 682) and outer diameter side (Rotary mechanical seal, PLAN53A flushing scheme in API 682). The results show that the local pressure drop in the sealing liquid film is the main cause result to cavitation of liquid film. The inner diameter side pressure fluctuation has a great impact on the end face cavitation, and the wave peak is about 100 times that of the outer diameter side pressure. The inner diameter side pressure fluctuation should be avoided in engineering application. There is hysteresis between gas volume fraction (GVF) and boundary pressure fluctuation. The synchronization between sealing performance parameters and outlet pressure fluctuation is good, but there is phase difference with inlet pressure fluctuation. The inner diameter side pressure fluctuation has a great change on the sealing performance. The peak is about 5–20 times that of the outer diameter side pressure, which is easy to cause vibration of the mechanical seal. The amplitude and period of pressure fluctuation have a great impact on the GVF and sealing performance. The larger the fluctuation period is, the less obvious the hysteresis of GVF is, and the closer to the variation law of pressure fluctuation. During the actual operation of the oil-gas multiphase pump, the mechanical seal connected with the medium in the pump is rotary, and the flushing scheme ought to be PLAN53A to ensure the safe and stable operation of the oil-gas multiphase pump.

Study on Leakage Model of Typical Penetration of Closed Structures Based on Porous Media Seepage Theory

Quantitative prediction of penetration leakage rate has not been reported so far. The theoretical prediction method of leakage rate of typical penetration static seal structure of closed structure is studied. Based on porous media seepage mechanics, the relationship between leakage rate and microstructure parameters is established, and a new prediction model of the leakage rate of sealing structures is proposed. Then, the relationship between seal-specific pressure and microstructure parameters is obtained by the Hertz contact mechanics model. Finally, the leakage rate calculation, which is independent of any experimental data, is obtained innovatively. The new model is used to predict the leakage rate of penetration, and the theoretical prediction results are compared with the experimental measurement results. It is proved that the two agree well, which verifies the effectiveness of the model. The prediction model based on this method can well reflect the effects of rough surface morphology, material mechanical properties, sealing load, high temperature, and high pressure on the leakage rate. The leakage rate prediction model proposed in this paper is independent of the experimental regression coefficient and can realize the conversion relationship between different sealing media, sealing materials, and working conditions.

Fluid Leakage in Static Rubber Seals

Interfacial surface roughness can result in fluid leakage of seals, and in the design of seals it is standard to give an upper limit for the surface root-mean-square (rms) roughness amplitude h_text{rms}. However, h_text{rms} is determined mainly by the long-wavelength roughness, which is (nearly) irrelevant for the sealing. I discuss the parameters which determine the leakage of seals, and present results for static rubber seals with circular cross-section (like rubber O-rings). I also study the influence of the fluid pressure on the interfacial surface separation and the leakrate.Graphical

Iron Loss Analysis and Efficiency Calculation of Double Stator HTS Machine With Stationary Seal

This paper mainly analyzes the iron loss of a double stator high-temperature superconducting (HTS) machine with stationary seal and calculates its efficiency. Firstly, according to the field-modulation theory, the air-gap flux density harmonic components of the excitation magnetic field and armature-reaction magnetic field are derived. Secondly, the air-gap flux density harmonic components corresponding to the flux density harmonic components of iron core are derived, and the main iron core flux density harmonic components are confirmed and verified by finite element analysis (FEA). When using the semi-FEA method to calculate the iron loss, according to the analysis results of main core flux density harmonic components, the appropriate step-interval of the FEA is selected. In addition, according to the characteristics of the iron core flux density, this paper proposes an alternative method of iron core flux density, which greatly shortens the calculation time of semi-FEA method of iron loss calculation. Then, iron loss model with variable coefficients is used to calculate the iron loss of the machine, and the calculation results are compared with those of the FEA iron loss calculation method. Finally, other losses and efficiency of the machine are calculated.

Development of a test-rig for advanced rotor–stator seals used in jet engines: Part II

Advanced rotor–stator seals are becoming more and more common in the latest generation of jet engines. In order to develop new radial seals and fully understand existing ones, testing needs to be done under full-scale conditions. It is necessary to be able to evaluate a new seal concept at “scale one”, under representative operating temperatures, pressure and rotational speed. This article – published in two instalments – presents details of an advanced new test-rig that is able to achieve this goal. It describes many facets of its design, construction, commissioning and use, and the challenges associated with its development.

Leakage Model of Metal Static Seal with Two Rough Surfaces Based on the Theory of Porous Medium

Leakage Model of Metal Static Seal with Two Rough Surfaces Based on the Theory of Porous Medium

Dynamic failure analysis of static seals under pressure fluctuation in an ultrahigh-pressure water piston pump

For ultrahigh-pressure piston pumps, in the reciprocating action of the piston, the fretting between the static face seal and the mating surface occurs with the change of the pressure in the piston chamber. This phenomenon will seriously affect the service life of the seal ring and lead to the failure of the pump. However, the failure of static seals used to seal ultrahigh-pressures is usually studied from the directions of shear, stress, or rubber material. These studies cannot explain the failure phenomenon of the sealing ring found in our experiment. This paper analyzed the failure of the face seal ring in a piston pump with a maximum pressure of 120 MPa. A two-dimensional axisymmetric finite element model was established based on the Mooney-Rivlin constitutive relation of the rubber material, and the fretting conditions of the sealing ring were analyzed. Combined with the wear scars observed by the scanning electron microscope the face seal ring’s dynamic failure mechanism on the ultrahigh-pressure piston pump was determined. A better sealing scheme was proposed and verified by the duration test of the pump, which provided a basis for the design of the sealing of the ultrahigh-pressure fluid with high-frequency fluctuations.

Development of a test-rig for advanced rotor–stator seals used in jet engines: Part I

Advanced rotor–stator seals are becoming more and more common in the latest generation of jet engines. In order to develop new radial seals and fully understand existing ones, testing needs to be done under full-scale conditions. It is necessary to be able to evaluate a new seal concept at “scale one”, under representative operating temperatures, pressure and rotational speed. This article – published in two instalments – presents details of an advanced new test-rig that is able to achieve this goal. It describes many facets of its design, construction, commissioning and use, and the challenges associated with its development. The first instalment, which appears here, looks at key characteristics of the test-rig, provides an overview of its mechanical design and airflow loop, and lists associated references. The second instalment will be published in the January 2022 issue of Sealing Technology.

Study on Improving the Sealing Reliability of Fluid Connector

Aiming at the problem of sealing reliability of fluid connector products commonly used in hydraulic system, this paper studies the static seal and the sliding seal. The factors affecting the sealing such as spring force, sealing ring and life of spring are considered one by one and the sealing effect is teseted. The results showed that improved fluid connector can ensure that the hydraulic system is in the state of not even air intake or oil leakage while connecting and disconnecting at any time. The connector has been successfully applied to a certain model of launch vehicle.

Impact Investigation of Stator Seal Leakage on Aerodynamic Performance of Multistage Compressor

In this paper, a numerical model based on the mass flow rate of seal leakage is presented, and a 3D numerical method of a multistage axial compressor with good engineering practicability is established. Validation consists of modeling a nine-stage axial compressor in all operating rotation speeds and calculating results of the performance characteristic curves in good agreement with test data. Comparisons are made against different cases of seal leakage mass flow rate for analyzing the impact of increasing seal leakage on the aerodynamic performance of the multistage axial compressor. The results indicate that the performance of the nine-stage axial compressor is degenerated faster and faster with seal leakage increasing in all operating working points, and the degeneration of performance of this compressor can be evaluated by the relationships of main performance parameters with the mass flow rate of seal leakage. Comparisons of flow distribution in the compressor for different cases of seal leakage also show that stators located in front stages of the multistage axial compressor are affected more seriously by the increasing seal leakage, and it can be confirmed that relatively larger flow losses in front stages bring significant impact on the decay of aerodynamic performance of a multistage axial compressor.

Fretting Wear of Rubber Sealing Ring Caused by Fluid Pressure Fluctuation

In the process of gas charging and discharging of gas cylinder, the fluid pressure fluctuates causing fretting wear of rubber sealing ring, which affects the sealing performance. The model of O-ring that installed at the mouth of the gas cylinder was established to study the fretting wear in the static seal. Effects of fluid pressure, compression ratio, friction coefficient and temperature on the fretting wear of the O-ring were considered. The results show that the fretting wear of O-ring can be divided into non-contact region, slip region and sticky region. In the static seal, the compression ratio and friction coefficient are the main factors affecting the fretting wear. The sealing performance is greatly influenced on the compression ratio and it is less affected by the temperature. The junction of slip region and sticky region has the greatest probability of seal failure.

Optimal design of large gap magnetic fluid sealing device in a liquid environment

Magnetic fluid seals (MFSs) have been widely used as a gas seal because of its advantages such as low wear, zero leakage, and long service life. However, the MFS is generally unstable due to structural- and material-related challenges in a liquid environment. To improve the pressure resistance and durability of the sealing liquid, we proposed an improved structure, where the annular pole component is designed as a radially magnetized annular permanent magnet. Furthermore, the structural parameters are optimized to maximize the magnetic induction intensity in the sealing gap. An MFS test device was simultaneously designed, according to the optimized results, to test the pressure resistance and durability under static and dynamic conditions. The results show that the pressure resistance and durability of the improved MFS structure is better than those of the traditional structures, specifically for a large gap structure. Furthermore, in a static seal, the sealing performance depends on the magnetic fluid magnetic saturation rather than other physical parameters, while in dynamic sealing, although magnetic saturation is a primary factor, the viscosity of the magnetic fluid also affects the sealing performance. Furthermore, the high-viscosity magnetic fluid had a higher critical pressure, while the low-viscosity magnetic fluid improved the durability of the seal. This result provides a reference for designing a magnetic fluid sealing device in a liquid environment.

Swelling Behaviour of Static Seals in Redox Flow Batteries

Swelling Behaviour of Static Seals in Redox Flow Batteries

A HTS Stator-Excited Axial-Flux Magnetic Gear With Static Seal

This paper proposes a novel high-temperature superconducting stator-excited axial-flux magnetic gear (HTS-SEAFMG) for the high-torque transmitting system. The proposed magnetic gear combines the merits of both HTS-excitation and stator-excitation. By using the HTS-excitation, a high air-gap flux density can be easily obtained, thus achieving the high torque density. The HTS-excitation windings are placed on the stator with a static seal of cooling Dewar which greatly reduces the manufacturing difficulty and the cost of refrigeration system compared with the dynamic seal. Thanks to the stator-excitation pattern, both the high-speed rotor and the low-speed rotor comprise only iron, thus contributing to the high mechanical reliability. The axially sandwich structure can also simplify its assembly in the high torque transmission applications. The dimensional parameter optimization and the electromagnetic performance evaluation are conducted by using the finite element method, respectively. The results show that the torque density of the proposed HTS-SEAFMG can reach 123 kNm/m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> . Theoretical analysis and results are both given to verify the feasibility of the proposed HTS magnetic gear design.

Analytical Modeling and Design of Novel Conical Halbach Permanent Magnet Couplings for Underwater Propulsion

Permanent magnet couplings can convert a dynamic seal into a static seal, thereby greatly improving the stability of the underwater propulsion unit. In order to make full use of the tail space and improve the transmitted torque capability, a conical Halbach permanent magnet coupling (C-HPMC) is proposed in this paper. The C-HPMC combines multiple cylindrical HPMCs with different sizes into an approximately conical structure. Compared with the conical permanent magnet couplings in our previous work, the novel C-HPMC has better torque performance and is easy to process. The analytical calculation method of transmitted torque of C-HPMC is proposed on the basis of torque calculation of the three common types of HPMCs. The accuracy of the torque calculation of the three HPMCs is verified, and the torque performance of the three HPMCSs of different sizes is compared and discussed. The “optimal type selection” method is proposed and applied in the design of C-HPMC. Finally, on the basis of torque analysis calculation and axial force calculation, a complete flowchart of the design and performance analysis of C-HPMC is described.

Investigation of a Novel Radial Partitioned Stator HTS-Excitation Flux-Switching Machine

This paper proposes and analyzes a novel radial partitioned stator HTS-excitation flux-switching (RPS-HTSFS) machine. The key is that the single ring-shaped HTS-excitation coil is independently placed in the coaxial claw-pole outer stator while the armature windings are wound around the U-shaped iron core on the inner flux-switching armature stator without permanent magnets. This solution has been explored to realize the physical isolation of armature winding and excitation winding, relieving the influence of armature field on the HTS-excitation coil. Moreover, only a single ring-shaped HTS-excitation coil is employed, therefore, reducing the HTS wires and the bending strain of the HTS-excitation coil. Also, the special refrigeration system can realize stationary seals of the double-layer ring-shaped cooling Dewar pattern, improving the cooling performance. By using the three-dimensional finite element analysis (3D-FEA), the machine performances are investigated and the validity of the proposed machine is verified.

Design and Analysis of 10 MW HTS Double-Stator Flux-Modulation Generator for Wind Turbine

Due to the advantage of stationary seal structure, HTS double-stator flux-modulation direct-drive generators (HTS-DSFMDDGs) have been proposed and researched. In order to investigate HTS-DSFMDDGs for large offshore wind turbines, the design and analysis of the machine have been conducted in this paper. Firstly, the generator structure and the principle are introduced and the parameter optimization procedure is described. Then, the influence of design parameters such as pole number of field coils, pole ratio (ratio of rotor pole-pair number to armature coil pole-pair number) and diameter of air-gap on the performance, in terms of mass and cost of active material, is presented. Finally, the optimal parameter for the 10 MW HTS-DSFMDDG is determined.

Performance Analysis of a New HTS-Excitation Claw-Pole Doubly-Salient Machine

This paper proposes a new 12-slot/10-pole high-temperature superconducting excitation claw-pole doubly-salient (HTS-CPDS) machine with a single HTS-excitation unit using stationary seal cooling. The key advantage of adopting claw-pole structure is that a ring-shaped HTS-excitation coil can be easily wound and artfully placed in the claw-pole cavity to realize the design of single excitation unit, and thus the cooling Dewar design for stationary seal is easily implemented. Also, due to using HTS-excitation, the air-gap flux can be flexibly regulated by changing the HTS current, thus keeping a constant amplitude of phase back-EMF under different rotor speeds. The cooling Dewar construction and the key parameter optimization are illustrated in detail. And compared to a counterpart employing the discrete racetrack HTS coils, the proposed machine can significantly reduce the HTS wire consumption and electromagnetic stress to a certain extent, thus cutting the cost and improving the anti-quench ability. By using the finite element analysis (FEA), the machine electromagnetic performances are evaluated, and its validity is verified.

Numerical Simulation of Static Seal Contact Mechanics Including Hydrostatic Load at the Contacting Interface

A finite element model of a static seal assembled in its housing has been built and is utilized to study how the seal deforms under varying loading conditions. The total contact load on the sealing surface is balanced by the sealed fluid pressure and the friction between the seal and the housing sidewall perpendicular to the sealing surface. The effect of the sealed fluid pressure between the sealing surfaces was investigated and the simulation showed that the surface profile is distorted due to the hydrostatic pressure. We study the distorted contact profile with varying sealed fluid pressure and propose five parameters to describe the corresponding contact pressure profile. One of these parameters, overshoot pressure, a measure of the difference between maximum contact pressure and the sealed fluid pressure, is an indicator of sealing performance. The simulations performed show different behaviors of the overshoot pressure with sealed fluid pressure for cosinusoidal and parabolic surfaces with the same peak to valley (PV) value.