Non-contacting Seals Research Articles

Analysis of dynamic characteristics of spiral groove liquid film seal under thermal–fluid–solid coupling

Purpose The purpose of this paper is to investigate the dynamic characteristics of spiral groove liquid film seal under the effect of thermal–fluid–solid coupling. Design/methodology/approach The dynamic analysis model of spiral groove liquid film seal under the effect of thermal–fluid–solid coupling was established by perturbation method. The steady-state and perturbation Reynolds equations were solved, and the steady-state sealing performance and dynamic characteristic coefficients of the liquid film were obtained. Findings Compared with the liquid film without coupling method, a divergent seal gap is formed between the seal rings under the effect of thermal–fluid–solid coupling, the minimum liquid film thickness decreases, the dynamic stiffness and damping coefficients of the liquid film are increased and the thermoelastic deformation of the end-face improves the dynamic performance of the liquid film seal. Originality/value The dynamic characteristics of the spiral groove liquid film seal under the effect of thermal–fluid–solid coupling are studied, which provides a theoretical reference for optimizing the dynamic performance of the non-contacting liquid film seal.

Physical modeling of a skip pneumatic winder

Introduction. The analytical phase of research on mine skip pneumatic winders has been passed, so the theoretical provisions have to be tested by the methods of physical modeling which is aimed at confirming the mathematical model adequacy and assessing the effectiveness of different types of sealing devices. Research methods. Physical modeling phases have been formulated, including modeling by geometric and aerodynamic similarity criteria, constructing aerodynamic characteristics of the installation, carrying out experiments with non-contacting and combined seals, and calculating the values of the installation volumetric efficiency based on the experimental data obtained. Research results. The lifting time of the skip model with different masses of material and seal types has been determined. The installation working points in the “flow rate–pressure” coordinate system have been identified, and the values of the volumetric efficiency have been calculated for each working point. Analysis of the results. A satisfactory convergence of calculated and experimental parameters of the physical model has been established. The model's volumetric efficiency has reached a technically acceptable level. The expected value of the experimental model’s volumetric efficiency has been calculated according to the similarity constants. Conclusions. The model's study revealed the convergence of the experimentally obtained volumetric efficiency of the model with its calculated values and proved the applicability of the mathematical model to experimental sample parameters calculation. The volumetric efficiency of the installation with both non-contacting and combined seals is quite high allowing to recommend the studied sealing devices for mine pneumatic winders.

Ultra-high-speed TEHL characteristics of T-groove face seal under supercritical CO2 condition

Purpose The purpose of this paper is to acquire sealing properties of supercritical CO2 (S-CO2) T-groove seal under ultra-high-speed conditions by thermo-elastohydrodynamic lubrication (TEHL) analysis. Design/methodology/approach Considering the choked flow effect, the finite difference method is applied to solve the gas state equation, Reynolds equation and energy equation. The temperature, pressure and viscosity distributions of the lubricating film are analyzed, and sealing characteristics is also obtained. Findings The face distortions induced by increasing rotational speed leads to the convergent face seal gap. When the linear velocity of rotation exceeds 400 m/s, the maximum temperature difference of the sealing film is approximately 140 K, and the viscosity of CO2 is altered by 17.80%. Near the critical temperature point of CO2, while the seal temperature increases by 50 K, the opening force of the T-groove non-contact seal enhances by 20% and the leakage rate declines by 80%. Originality/value The TEHL characteristics of the T-groove non-contact seal are numerically analyzed under ultra-high-speed, considering the real gas effect and choked flow effect. In the supercritical conditions, the influence of rotational speed, seal temperature, seal pressure and film thickness on sealing performance and face distortions is analyzed.

Experimental Investigations on the Pressure Fluctuations in the Sealing Gap of Dry Gas Seals With Embedded Pressure Sensors

Abstract Dry gas–lubricated noncontacting mechanical seals (DGSs), most commonly found in centrifugal compressors, prevent the process of gas flow into the atmosphere. Especially when high speed is combined with high pressure, DGS is the preferred choice over other sealing alternatives. Even though the noncontacting seal is proved reliable, the ultrathin gas film can still lead to a host of potential problems due to possible contact. In order to investigate the flow field in the sealing gap and to facilitate the numerical prediction of the seal performance, a dedicated test facility is developed to carry out the measurement of key parameters in the gas film. Gas in the sealing film varies according to the seal inlet pressure, and the thickness of gas film depends on this fluctuated pressure. In this paper, the test facility, measurement methods, and the first results of static pressure measurements in the sealing gap of the DGS obtained in the described test facility are presented. An industry DGS with three-dimensional grooves on the surface of the rotating ring, where experimental investigations take place, is used. The static pressure in the gas film is measured, up to 20 bar and 8100 rpm, by several high-frequency ultraminiature pressure transducers embedded into the stationary ring. The experimental results are discussed and compared with the numerical model programed in matlab (Luo, J., Dohmen, H. J., and Benra, F. K., 2018, “Coupled Thermal-Structural-Fluid Numerical Analysis of Gas Lubricated Mechanical Seals,” ASME Paper No. GT2018-75458), the characteristic and magnitude of which have a good agreement with the numerical simulations. It suggests the feasibility of measuring pressure profiles of the standard industry DGS under pressurized dynamic operating conditions without altering the key components of the seal, and thereby affecting the seal performance.

Optimizing the Geometric Parameters of a Straight-Through Labyrinth Seal to Minimize the Leakage Flow Rate and the Discharge Coefficient

A straight-through labyrinth seal is one of the most popular non-contacting annular seals through which energy dissipation by turbulence viscosity interaction is achieved with a series of teeth and cavities. The geometric parameters of the straight-through labyrinth seal, such as clearance, tooth width, tooth height, cavity width, and tooth inclination angle, affect its performance. The space for installing a labyrinth seal in turbomachinery is limited, and so it is important to optimize its geometry for a fixed axial length in order to minimize the leakage flow rate and the discharge coefficient. The objective of the current study is to understand the effects of changing the geometric parameters of the seal on the leakage flow rate and the discharge coefficient, and to determine the optimized geometry for a fixed axial length. When the whole axial length is fixed, the most effective way to decrease the discharge coefficient is to reduce the cavity width by increasing the number of cavities. However, if the number of cavities is too high, the beneficial effect of more cavities can be reversed. The results of this study will help turbomachinery manufacturers to design a more efficient labyrinth seal. Numerical simulations of leakage flow for the straight-through labyrinth seal were carried out using Reynolds-Averaged Navier–Stokes (RANS) models, and the results for their discharge coefficients and pressure distributions were compared to previously published experimental data.

A numerical solution of temperature distribution in the clearance and the sealing rings of the non-contact face seal

The study presents a numerical analysis of the temperature distribution in the clearance and the temperature distribution in the rings of a non-contact face seal. Non-contact face seals designed for turbine pumps to meet the requirements of lower leakage, longer life, and more frequent starting and stopping are included in this test. A thermo-hydro-mechanical model of the non-contact face seal clearance has been presented. Based on this model, dimensionless differential equations were derived to determine the temperature distribution in the clearance seal gap and the temperature distribution in sealing rings. The numerical solution of differential equations allowed the presentation of temperature characteristics for different parameters of the analyzed non-contact face seal. The analysis took into account hydrodynamic and thermodynamic phenomena in the clearance of the face seal depending on pressure, leakage flow rate and temperature of the sealing fluid, clearance dimensions, thermal parameters of the sealing rings, and operation parameters of the rotating machine. The temperature distribution in a non-contact face seal can also be used to determine the thermal deformation of the sealing rings. The presented numerical model is useful in the design of non-contact face seals because it allows the selection of parameters stabilizing the thermo-hydro-mechanical state of the two mating sealing rings.

Experimental Study on the Performance of a See-Through Labyrinth Seal With Two-Phase, Mainly-Liquid Mixtures

Abstract With the increasing demand of the oil and gas industry, many pump companies are developing multiphase pumps, which can handle liquid–gas flow directly without separating the liquid from a mixed flow. The see-through labyrinth seal is one of the popular types of noncontact annular seals that act as a balancing piston seal to reduce the axial thrust of a high-performance centrifugal pump. The see-through labyrinth seal also generates reaction forces that can significantly impact the rotordynamic performance of the pump. Multiphase pumps are expected to operate from pure-liquid to pure-gas conditions. Zhang and Childs (2019) (Zhang, M., and Childs, D., 2019, “A Study on the Leakage and Rotordynamic Performance of a Long Labyrinth Seal Under Mainly-Air Conditions,” ASME J. Eng. Gas Turbines Power, 141(12), p. 121024) conducted a comprehensive experimental study on the performance (leakage and rotordynamic coefficients) of a see-through labyrinth seal under mainly gas conditions. This paper continues Zhang and Childs (2019) (Zhang, M., and Childs, D., 2019, “A Study on the Leakage and Rotordynamic Performance of a Long Labyrinth Seal Under Mainly-Air Conditions,” ASME J. Eng. Gas Turbines Power, 141(12), p. 121024) research and studies the performance of the see-through tooth-on-stator labyrinth seal under mainly liquid conditions. The test seal's inner diameter, length, and radial clearance are 89.256 mm, 66.68 mm, and 0.178 mm, respectively. The test fluid is a mixture of air and paper silicone oil (PSF-5cSt), and the inlet gas volume fraction (GVF) varies from zero to 12%. Tests are conducted at an exit pressure of 6.9 bars, an inlet temperature of 39.1 °C, three pressure drops (PDs) (27.6 bars, 34.5 bars, and 48.3 bars), and three rotating speeds ω (5 krpm, 10 krpm, and 15 krpm). The seal is always concentric with the rotor, and there is no intentional fluid prerotation at the seal inlet. The air presence in the oil flow significantly impacts the leakage as well as the dynamic forces of the test seal. The first air increment (increasing inlet GVF from 0% to 3%) slightly increases the leakage mass flow rate, while further air increments steadily decrease the leakage mass flow rate. For all test conditions, the leakage mass flow rate does not change as ω increases from 5 krpm to 10 krpm but decreases as ω is further increased to 15 krpm. The reduction in the leakage mass flow rate indicates that there is an increase in the friction factor, and there could be a highly possible flow regime change as ω increases from 10 krpm to 15 krpm. For ω ≤ 10 krpm, effective stiffness Keff increases as inlet GVF increases. Keff represents the test seal's total centering force on the pump rotor. The increase of Keff increases the seal's centering force and would increase the pump rotor's critical speeds. Ceff indicates the test seal's total damping force on the pump rotor. For ω ≤ 10 krpm, Ceff first decreases as inlet GVF increases from zero to 3%, and then remains unchanged as inlet GVF is further increased to 12%. For ω = 15 krpm, Keff first increases as inlet GVF increases from zero to 3% and then decreases as inlet GVF is further increased. As inlet GVF increases, Ceff steadily decreases for ω = 15 krpm.

A Method for Estimating on Dynamic Characteristics of Non-Contact Seals With a Surface Texture

A Method for Estimating on Dynamic Characteristics of Non-Contact Seals With a Surface Texture

Mathematical modeling of centrifugal machines rotors seals as dynamic systems

The possibilities of using axial and radial contactless seals as static and dynamic supports of the centrifugal machine rotor are considered. A model of the hydromechanical system rotor - groove seals has been built. Analytical relationships that describe the radial - angular oscillations of a centrifugal machine rotor in groove seals are obtained. Figs.: 3, Refs.: 12 titles.Keywords: mathematical modeling; hydromechanical system; radial-angular vibrations, radial non-contact seal.

Effects of Clearance on the Performance of a Labyrinth Seal Under Wet-Gas Conditions

Abstract The labyrinth seal is one of the most popular noncontact annular seals used in centrifugal compressors to improve machine efficiency by reducing the secondary flow leakage. Reducing the radial clearance Cr can effectively decrease the seal's leakage and therefore increase the machine efficiency. However, reducing Cr can also introduce undesired effects on the machine's vibration behaviors. This paper experimentally studies the impact of reducing Cr on the leakage and rotordynamic coefficients of a 16-tooth see-through labyrinth seal under wet-gas conditions. The test seal's inner diameter is 89.256 mm. Two rotors with different diameters are used to obtain two radial clearances (0.102 mm and 0.178 mm). Tests are carried out at a supply pressure of 62 bars, three speeds from 10 krpm to 20 krpm, three pressure ratios from 0.21 to 0.46, and six inlet liquid volume fractions (LVFs) from zero to 15%. The test fluid is a mixture comprised of air and silicon oil. Test results show that, for all pure-air and mainly air conditions, decreasing Cr decreases (as expected) the test seal's leakage mass flowrate. For all test cases, direct dynamic stiffness KΩ is negative, producing a negative centering force on the associated rotor. For inlet LVF ≤ 8%, the effects of decreasing Cr on KΩ are negligible. When inlet LVF = 12% and 15%, decreasing Cr increases KΩ (decreases the magnitude). In other words, when inlet LVF = 12% and 15%, decreasing Cr reduces the test seal's negative centering force on the rotor, and would increase the critical speeds of the rotor. The value of the effective damping Ceff near 0.5ω represents the seal's capability to suppress the rotor's potential whirling motion at about 0.5ω. For all pure-air and mainly air conditions, decreasing Cr generally increases the Ceff value near 0.5ω; i.e., decreasing Cr improves the test seal's stabilizing capability against the rotor's potential whirling motion at about 0.5ω.

Influence of Thermoelastic Phenomena on the Energy Conservation in Non-Contacting Face Seals

The purpose of this study was to develop a mathematical model for non-contacting face seals to analyze how their performance is affected by thermoelastic phenomena. The model was used to solve thermal conductivity and thermoelasticity problems. The primary goal was to calculate the values of thermal deformations of the sealing rings in a non-contacting face seal with a flexibly mounted rotor (FMR) for a turbomachine. The model assumes the conversion of mechanical energy into heat in the fluid film. The heat flux generated in the fluid film is transferred first to the sealing rings and then to the fluid surrounding them. Asymmetric distribution of temperature within the sealing rings leads to the occurrence of thermal stresses and, consequently, a change in the geometry of the rings. The model is solved analytically. The distributions of temperature fields for the sealing rings in the cross-sections are calculated using the Fourier-Bessel series as a superficial function of two variables (r,z). The thermoelasticity problems described by the Navier equations are solved by applying the Boussinesq harmonic functions and Goodier’s thermoelastic displacement potential function. The proposed method involves solving various theoretical and practical problems of thermoelasticity in FMR-type non-contacting face seals. The solution of the mathematical model was made use of analytical methods, and the most important obtained results are presented in graphical form, such as the temperature distributions and axial thermal distortions in cross-sections of the rings. The calculated thermal deformations of the sealing rings are used to determine the most important seal performance parameters such as the leakage rate and power loss. The article also presents a multi-criteria analysis of seal rings materials and geometry, which makes it easier to choose the type of materials used for the sliding rings.

Investigation on Leakage Characteristics of Two Kinds of Injection-type Shaft Seals Using CFD

Recently, injection-type shaft seals (non-contact type seals) started replacing their counterparts called mechanical seals (contact-face type seals) in power plant feedwater pumps. Both of these seals have primary function of preventing the fluid inside the pump pressure casing from leaking to outside of the pump. Mechanical seals are reported to fail rapidly and abruptly in especially power plant feedwater pumps because of increased speeds and the feedwater temperatures. If mechanical seals fail, most often the pump must be shut-down immediately and put the pump reliability in question. Hence, the injection-type shaft seals were introduced in order to avoid reliability problems associated with mechanical seals and save maintenance costs of feedwater pumps. Therefore, in this paper we investigated the performance of injection-type shaft seals particularly with labyrinth and plain annuls designs. Research findings show that design parameters such as seal clearance and diameter play an important role in determining the injection-type shaft seal’s leakage, while drain temperature was un-affected by these design parameters.

Steady and Transient Thermal State of Turbine Disk Estimation for Life Time Monitoring

Abstract In connection with increasing intensification of the working process in a gas turbine engine and increasing requirements for economy, the problem of defining and monitoring the main parts lifetime is becoming more vital. Modern algorithms of the monitoring systems are based on taking into account the levels of part temperature and total equivalent stress throughout the flight cycle. Thermal and stress-strain states of the critical zones of the main parts are determined on the basis of information received from the sensors installed in the engine gas path. Turbine disks are located in the internal cavities of the engine and are cooled by air from the compressor. However, in some designs, the disk cavity can be separated from the place of cooling air bleed by several stages of non-contact labyrinth seals, which will lead to some delay in changing the parameters of the cooling air flow when changing the engine operating mode. It has been observed that if this situation is not taken into account, it can lead to significant errors (more than 40%) in determining the lifetime for the peripheral zone of the disk. At the same time, this error is minimal for the hub and the middle zone of the disk, and the existing monitoring algorithms can be used.

Creative Design of Streamline Groove Mechanical Seal Based on TRIZ Theory

In view of the problems of poor stability and large leakage of dynamic pressure non-contact mechanical seals in a specific working environment, through the analysis of the mechanical seal principles and end structure, based on the TRIZ theory, choose the “structure stability”, “adaptability and versatility” as the improve elements, the “harmful emission” and “foreign harmful factors” as the deteriorate elements. The principle numbers of the invention are obtained from the contradiction matrix. According to the principles of the invention, a new type of streamline groove mechanical seal is designed. Through the technology of making groove on the end face, a fluid film with a certain stiffness is obtained, and the end face is sealed. Through improve the stability and adaptability of the mechanical seal operation, it can operate safely and stably in a specific working environment and meet the requirements of the seal.

Computational analysis for scallop seals with sickle grooves, part I: Leakage performance

Reducing of leakage rate of annular seals is an important objective of sealing technology. A number of noncontact seals are used for hermetic sealing of centrifugal compressors shafts such as: annular, labyrinth, honeycomb, hole pattern, pocket and scallop seals. In the art, scallop seals are of great interest in terms of reducing costs and time of manufacture. This paper presents results of calculation of leakage rate characteristics of scallop seals with sickle grooves (SSSG) depending on seal geometry. The Computational Fluid Dynamics (CFD) technique is used for calculation of hydrodynamic characteristics of seal. The Design of Experiment (DOE) technique is used for analysis of influence of scallop depth and width, rib width and number of scallops in circumferential direction on sealing performance of scallop seal. Such a comprehensive approach to the calculation using computational methods allows improving and further optimizing the existing designs of scallop seals.

Transient response and rub-impact phenomenon of liquid lubricated non-contacting mechanical seals during external pressure fluctuation

The purpose of this paper is to investigate the dynamic contact behavior and transient response of liquid lubricated non-contacting mechanical seals during external pressure fluctuation. The presented model of spiral groove mechanical seals includes the Reynolds equation considering surface roughness and mass-conserving cavitation boundary, elastoplastic asperity contact model expressing rub-impact phenomenon, as well as the dynamic equation describing the vibrations of stator which were solved simultaneously with a numerical method. Results indicate that the vibration amplitude and frequency of sealing performances are affected significantly by the external pressure. The increment of rotational speed avoids face rub-contact and reduces the instantaneous variation of leakage. The results presented in the study are expected to provide a theoretical guidance to improve stability and safety of sealing system.

Development of a friction test apparatus for simulating the ultra-high pressure environment of the deep ocean

The continued development of deep-ocean equipment requires improved friction and wear resistance of key tribopairs in a high pressure environment. However, there is little research on the effect of high hydrostatic pressure on the tribological properties of different tribopairs as available test rigs are scarce. In this work, a friction test apparatus was developed to help carry out this research. A non-contact gap seal and uniquely shaped loading system were developed to adapt to the high pressure environment and improve measurement accuracy. The fatigue life simulation of key components was conducted to ensure the safety and reliability of the apparatus. Pilot studies on tribopairs consisting of 30 vol% carbon fiber-reinforced polyetheretherketone (CFRPEEK) and AISI 431 stainless steel (431SS) lubricated with high-pressure water were conducted. The results indicated that the apparatus could work stably under an ultra-high hydrostatic pressure of 80 MPa. Friction was found to decrease with increasing hydrostatic pressure. Maximum wear of CFRPEEK occurred at 20 MPa. The results also showed that the CFRPEEK/431SS tribopair could be used in the deep ocean at depths of less than 8000 m as the friction and wear of the tribopair did not degenerate sharply for pressures of 0–80 MPa.

Non-Contacting Finger Seal Piston for Oil Less Engines

<div class="section abstract"><div class="htmlview paragraph">The current quest to reduce CO<sub>2</sub> emissions combined to new technologies has sparked an interest in revisiting radically different engine configuration concepts, such as adiabatic and split-cycle engines. To achieve the full potential of both concepts, the combustion chamber must be sealed without lubricating oil. A promising approach that has yet remained elusive, is to lubricate the piston-liner interface with gases. This paper explores the concept of using non-contacting finger seals to seal piston engines combustion chambers. The finger seals, made of a gas-lubricated pad at the end of a flexible beam, are fixed on a rotating piston that uses the centrifugal force to close the piston-liner gap. A physics-based fluid-structure model is developed to predict finger displacements and sealing performances. The model shows that the radial displacement of the fingers naturally creates a convergent profile with the liner that generates sufficient aerodynamic pressure to maintain a micrometer gap that prevents the piston to contact the liner. The results also show that the achievable leakage area would be similar to that of Wankel rotary engine and friction losses would be negligible compared to those of conventional piston rings. On the other hand, the study reveals challenges that will need to be addressed in order that finger seals be practical in engines, such as the finger torsion, dynamic behavior when exposed to bore distortion as well as the manufacturing tolerances required to ensure contact-free operation.</div></div>

Підвищення герметичності і екологічної безпеки ущільнень насосів АЕС

The determining factor for NPP pumps is safety, as well as the maximum sealing capacity, which imposes additional conditions when choosing the type of seal. Mechanical seals are widely used in pumps in nuclear power plants. The processes occurring at the junction of the contacting end surfaces of a seal in various operating modes are described. Cooling and safety pumps systems that pump radioactive media are subject to requirements, some of which can only be met with the use of special designs. On the basis of mechanical seals, new types of seals have been created, in which the sealing belts are unloaded and operate with a small gap in friction modes close to liquid: hydrodynamic and thermohydrodynamic seals. The principle of operation of thermohydrodynamic seals is based on the use of the deformation of the rings under the force of thermal stresses in the contact zone. At high pressure differentials and rotation speeds, when a long life is required and small leaks are allowed, seals with a continuous liquid film are used - hydrostatic seals. Impulse mechanical seals are self-adjusting non-contacting seals and are an alternative to hydrostatic and hydrodynamic non-contacting mechanical seals. Impulse mechanical seals with self-adjusting gap have a number of advantages over conventional mechanical seals and non-contacting hydrostatic and hydrodynamic mechanical seals. Seals with impulse balancing of the axially moving ring during the rotation of the shaft ensure contactless operation with low leaks, and during standstill — complete tightness. Examples of industrial application of impulse seals in pumping equipment of nuclear power plants were given.

Influence of Internal Flow in Lubrication Film on Temperature Distribution of Non-Contact Mechanical Face Seals

Influence of Internal Flow in Lubrication Film on Temperature Distribution of Non-Contact Mechanical Face Seals