Mechanical Seal Design Research Articles

Investigation on the dynamic characteristics for high-speed mechanical seal considering turbulent cavitating flow and inertia effect

PurposeThis study aims to investigate the dynamic characteristics of a high-speed mechanical seal by considering the flow regime, cavitation phenomenon and inertia effect.Design/methodology/approachBased on the high-speed conditions of a mechanical seal with a low-viscosity fluid, a multi-factor coupled lubrication model of a mechanical seal is established. The perturbation Reynolds equation set is derived using the perturbation method, and the effects of turbulent flow and inertia on sealing performance are discussed.FindingsThe results indicate that turbulence significantly influences the dynamic characteristics of low-viscosity fluids under high-speed conditions.Originality/valueThe results of the dynamic characteristics presented in this study are expected to provide guidance for the design of mechanical seals.

Sealing performance and optimization design of squamous textured mechanical seal

The work focuses on the optimization of surface texturing and their geometrical characteristics to improve the sealing performance of mechanical seal. The hydrodynamic model is developed to predict the sealing performance of four textures, including dimple, triangle, chevron and squamous textures. Result indicates that the squamous texture exhibits better sealing performance with high ratio of load-carrying capacity to leakage and ratio of oil film stiffness to leakage at various angular speeds and pressures. Furthermore, the functions of squamous texture characteristics with the load-carrying capacity and leakage ratio are revealed by the response surface methodology. And the squamous texture is optimized with high load-carrying capacity and low leakage ratio through the multi-objective optimization algorithm NSGA-II to achieve the Pareto-optimal set.

Influence of diamond-like carbon coatings and micro-texturing on friction and wear of seal interfaces: Experiment and simulation study

For mechanical seal friction vice in dry friction conditions, due to friction wear serious failure, is the slurry pump and other instruments in the operation of the process of the urgent need to solve the problem. In this paper, in order to optimize and enhance the friction and wear problem of mechanical seal end face of slurry pump. Surface treatment of mechanical sealing rings with diamond-like carbon (DLC) coating and surface microtexturing, and at different rotational speeds and normal forces, the surface hardness, wear coefficient and dry friction coefficient of the sealing rings were analyzed by experimental comparison, and the wear morphology was collected by electron microscopy, having analyzed the results of the sets of, the end face structure of the mechanical seal was optimized. Based on Archard wear model simulation calculations, the seal ring wear depth and wear quality were obtained. The results show: under dry friction conditions, the synergistic effect of the DLC coating and the surface micro-texture (MT), the coefficient of friction is reduced by approx. 68% and the quality and depth of wear is minimized. Excessive speeds and normal forces are more prone to wear behavior caused by abrasive wear. Simulation results of surface treatment groups, DLC / MT group maximum wear depth is the smallest; wear quality test and simulation of the maximum error within 15.7%. The results of the study can provide a basis for a phosphoric acid plant slurry pump mechanical seal design.

Optimization method of high parameter spiral groove mechanical seal based on axiomatic design theory

At present, in order to improve the performance of spiral groove mechanical seals, the structural parameters of seals are mostly adjusted based on the experience of designers. The integration degree of existing mechanical seal performance research examples is low, and the whole performance optimization process lacks of scientific theoretical framework to guide. In order to solve this problem, combining the axiomatic design theory with the existing mechanical seal performance research, a structural optimization method of spiral groove mechanical seal based on axiomatic design theory was put forward. This method defines the mapping relationship between the three-level functional requirement domain and the design parameter domain of the spiral groove mechanical seal, and thus develops 14×14 diagonal optimization matrix. The research results show that the introduction of axiomatic design provides a basic theoretical framework for the performance optimization of spiral groove mechanical seals and decomposes the optimization process into several design modules, which improves the efficiency and accuracy of the optimization design of spiral groove mechanical seals and has good application value.

Study on the effect of bubble number on the collapse of a multi-bubble system near the rigid wall

The mechanism of multi-bubble collapse is one of the key technologies that need to be overcome in the development of large submersibles, which is urgently needed to study and explore. The VOF method is used to study the collapse process of a multi-bubble system near the rigid wall. The bubble collapse process is analyzed under three different bubble numbers and four different initial bubble wall distances. The influence of the number of bubbles and initial bubble wall distance on the bubble collapse process is obtained, and the mechanism of multi-bubble collapsing near the rigid wall is revealed. The results indicate that in a multi-bubble system, as the number of bubbles increases, the duration of bubble collapse increases, the minimum bubble radius decreases, and the maximum central pressure increases. The closer the bubble is to the rigid wall, the longer the duration of bubble collapse, which also lead to fluctuations in the maximum center pressure and maximum interface velocity of a multi-bubble system. The results of this study are expected to provide a theoretical basis and technical support for the design and performance optimization of deep submersible mechanical seals.

Thermo-viscous influence on the mechanical seal performance in a reactor coolant pump (RCP)

The mechanical seal performance in reactor coolant pump (RCP) is of great importance for the efficient and safe operation of primary loop in nuclear power plant. The sealing medium filling inside the seal encounters strong thermal gradient. In this paper, thermo-viscous effect on sealing characteristics with two typical mechanical seal faces, namely the tapered-end-face and wave-tilt-dam, is numerically studied, by introducing the temperature-viscosity equation according to the real physical properties of the sealing medium. Performance of mechanical seal with two different temperature-viscosity equations are compared. In addition, the influence of thermo-viscous effect on cavitation is also analyzed. It is revealed that the temperature-viscosity variation significantly influences the internal flow field, temperature field, two-phase distribution, and the opening force as well. With low base film thickness, the temperature difference will reduce 58% as considering the thermal effect on viscosity, and the difference in leakage may be as high as 43%. Also, the prediction of cavitation under small film thickness indicates that the thermo-viscous effect decreases the cavitating area. This work contributes to the mechanical seal design and performance prediction by assessing the thermal influences on viscosity of seal medium, and meanwhile revealing the effect on the possible cavitation event.

Technology of Repairing the Active Main Pipeline Using Braze-Welded Couplings

Background. During operation, the main pipeline needs to be repaired. During periodic diagnostics of the pipeline state defects are detected, some of which are unacceptable. The classic repairing method, that involves the shutdown of the pipeline with subsequent replacement of its defective spots, requires significant financial costs and is associated with a forced pipeline outage and environmental violation.
 Objective. The purpose of this article is to improve the technology of reinforcing sections of main high-pressure pipeline with welded couplings, which are filled with molten metal by allowing obtaining high efficiency of pipe strengthening of medium and small diameters.
 Methods. Strength improvement of the active pipeline spots is realized by installing brazed-welded couplings on an active main pipeline. Strengthening the pipeline with the coupling consists in the redistribution of the load part from the pipe to the wall of the coupling, which leads to a decrease of the stress level in the pipe wall. The reinforcement efficiency of the pipeline could be evaluated by the degree of reduction of circumferential stresses in the fixed pipe wall.
 Results. The article suggests a technique for strength improvement of pipeline spots using couplings filled with a molten metal that has a high elasticity modulus. The operations of formation of under-coupling layer with the parameters that provide achievement of the maximum value of the stresses reduction degree in the reinforced pipe are proposed, while ensuring an even load distribution between the wall of the pipeline spot being repaired and the coupling shell. An improved technology for fixing defective spots of the active pipeline has been proposed, designs for front seals have been proposed that facilitate the formation of under-coupling layer with optimal parameters. The proposed technique makes it possible to increase the efficiency of the pipe strengthening of small and medium diameters.
 Conclusions. The article proposes an improved technology of the defective spots reinforcing of the active main pipeline using braze-welded coupling. The focus is on the design of mechanical seals that ensure the tightness of the under-coupling space during the formation of the coupling layer.
 Further research would be performed in the direction of developing a mathematical model of the pipeline reinforced with braze-welded coupling, taking into account temperature changes during heating and cooling of the coupling structures during the formation of the under-coupling layer. Some research will be also performed to improve the coupling structures and methods of quality control of their mounting on the pipe.

Performance Analysis of the Self-Pumping Hydrodynamic Mechanical Seal with a Conical Convergent Diffuser Groove

Requirements such as high opening force, low leakage rate, and design without matching auxiliary flushing systems are expected of the modern fluid machinery shaft seals used in the process industry. A self-pumping hydrodynamic mechanical seal with a conical convergent diffuser groove is proposed and its sealing performance is studied by numerical simulation in this paper. Further, its sealing performance is compared to that of a flat-bottomed equal cross-sectional diffuser groove and the results have shown that the proposed seal has more superior sealing performance. The influence of structural and operating parameters on the sealing performance of the proposed seal is discussed and its working mechanism is explained. The results have shown that when the structural parameters of the spiral groove and the operating parameters are the same, the proposed design has a similar leakage rate and a higher opening force. The conical convergent diffuser groove has better wrapping properties, whereas the fluid energy is utilized more efficiently, improving the sealing interface opening force. The taper degree variation causes a slight change to the pressure at the root of the spiral groove, causing slight fluctuations in the seal leakage rate. The research results broaden the design of non-contact mechanical seals and provide a theoretical basis for the engineering application of the proposed self-pumping hydrodynamic mechanical seal with a conical convergent diffuser groove.

Gas-Liquid Mass Transfer Behavior of Upstream Pumping Mechanical Face Seals.

For gas–liquid medium isolation seals in aero-engines, the upstream pumping function of directional grooves provides an effective way to realize the design of longer service life and lower leakage rate. However, this produces a new problem for gas–liquid mass transfer in the sealing clearance. This study establishes an analytical model to investigate the gas–liquid mass transfer behavior and the change rule for the opening force of mechanical face seals with elliptical grooves. Compared with traditional studies, this model considers not only the gas–liquid transfer but also the cavitation effect. The results obtained show that with the increase of rotational speed, the gas medium transferred from the inner low-pressure side to the outer high-pressure side. In addition, the leakage rate of the liquid medium from the outer high-pressure side to the inner low-pressure side increased with the growth of sealing clearance, rotational speed and seal pressure. The upstream pumping effect of the gas medium with elliptical grooves not only led to a state of gas–liquid mixed lubrication in the sealing surfaces, but also significantly increased the opening capacity of the seal face. This research may provide a reasonable basis for the design of upstream pumping mechanical face seals.

AES India invests in green technology

Aesseal Plc, a specialist in the design and manufacture of mechanical seals, bearing protectors, seal support systems and gland packing, says that its operation, based in Pune, India, is investing in green technology.

Static and dynamic characteristics of a Rayleigh-steps mechanical seal with reverse steps

This paper presents a Rayleigh-steps mechanical seal with reverse steps (RS-MS), and the governing equation was solved by the finite difference method (FDM). The effects of angular misalignment, working condition parameters, and film thickness on sealing performance were discussed, including the opening force, cavitation ratio, leakage rate, frictional torque, stiffness and damping coefficients. The results indicate that the cavitation phenomenon in the reverse step groove can restrain the leakage, while it also affects the stability of the seal. The angular misalignment makes the seal have greater stiffness and damping coefficients. The stiffness and damping coefficients decrease rapidly with the increase of the film thickness, and the dynamic stability of the mechanical seal decreases with the increase of the film thickness, which is not conducive to the stable operation of the seal. The research results can guide the optimization design of mechanical seals.

Analysis of stability of two-phase flow mechanical seal with spiral groove under high speeds

A thermo-hydrodynamic model was introduced by considering fluid film phase change to analyze the stability of a spiral groove mechanical seal under high speeds. The Reynolds equation, energy equation and heat conduction equation were solved using the finite difference method. Two kinds of phase state stability criteria and fluid film temperature or pressure distributions in each phase state were studied. Different phase states of fluid film and phase state stability of such a spiral groove mechanical seal under variable operating and geometry conditions were analyzed. The results show that vapor mass fraction volume ratio vs sealed fluid temperature (κ-Tf) curve and film pressure coefficient versus sealed fluid temperature (Km-Tf) curve can be used as phase state stability criteria which can predict the range of instability, stability and quasi-stability of a spiral groove mechanical seal. But the Km-Tf curve is more suitable for practical engineering applications. It is found that a significant change in pressure distribution will bring about instability of a spiral groove mechanical seal. The sudden change of film pressure distribution usually occurs when the leakage flow medium in the interface is in the transition phase from quasi-liquid to quasi-vapor where κλ=0 = κ0<λ<1 and κλ=1 = 0. Optimized design of a spiral groove mechanical seal will improve its stability during the phase change from liquid phase state to vapor phase state.

Multifield Coupling Model and Performance Analysis of a Hydrostatic Mechanical Seal

A two-dimensional axisymmetric thermal-fluid-solid coupled mathematical model of a contact mechanical seal is established. The finite difference method is used to solve the control equations for the fluid pressure and temperature of the seal end face, and the finite element method is used to determine the thermal deformation state of the seal. The seal’s performance at different working speeds was studied and verified by experiments. The results show that under the combined actions of thermal and mechanical deformations, the seal end face forms a convergent leakage gap from the outer diameter to the inner diameter. The minimum film thickness is observed on the inner diameter side of the seal end face, and the highest end face temperature coincides with this location. With increasing working speed, the contact force at the inner diameter side increases, the temperature difference between the inner diameter and the outer diameter of the end face increases, and the leakage rate correspondingly increases. The numerical simulation results are in good agreement with the experimental results. The model and calculation method can be applied to other forms of mechanical seal design and optimization.

Friction and wear behavior of different seal materials under water-lubricated conditions

The shaft mechanical face seal in a high-speed turbopump of a liquid rocket engine often operates under extremely harsh conditions. For example, a low-temperature and low-viscosity fluid (such as liquid oxygen or liquid hydrogen) is used as a lubricant. The performance of the seal rings, especially the friction and wear behavior, directly determines whether the seal functions normal. In this study, the friction and wear behavior of several ring materials are tested using a pin-on-disk tribo-tester, and the wear morphology of the ring is investigated. The friction coefficients (COFs) and mass-wear rates under dry-friction and water-lubricated conditions, which are used to simulate low-viscosity conditions, are obtained. The results show that at a pressure-velocity (PV) value of 2.4 MPa·(m/s), the COF between the copper graphite (stator) and copper-chrome alloy disk (rotor) is low (with a value of 0.18) under the dry-friction conditions, and the 5-min wear mass of the copper graphite is approximately 2 mg. Under the water-lubricated conditions, compared with other materials (such as copper-chrome alloy, S07 steel, alumina ceramic coating, and nickel-based calcium fluoride), the S07 steel with a diamond-like carbon film is preferred for use in a high-speed turbopump under extreme conditions. The results of this study can provide theoretical and experimental guidance in the design of mechanical face seals in liquid rocket engines.

An Axial and Torsional Percussion Hammer with Considerable Potential to Increase the Drilling Speed of High-Temperature Geothermal Wells

Geothermal energy is a kind of green and sustainable energy and an essential alternative energy in the future. Improving the drilling speed of geothermal wells is helpful for the efficient exploitation of geothermal resources. Axial & Torsional Percussion Hammer (ATPH) was proposed in this paper for drilling enhancement. ATPH can convert the kinetic energy of the drilling fluid to percussion load, and improve the rock-breaking efficiency of the bit. Because of its mechanical seal design, it can operate efficiently at temperatures over 200 °C, which proves that it can be used in geothermal wells. The large eddy simulation (LES) method is chosen to calculate the percussion load characteristics of the ATPH oscillator, including its main frequency and amplitude. In the field drilling experiments of two high-temperature wells, ATPH showed better ROP enhancement ability and longer working life than PDM. In the well interval drilled by ATPH, the maximum temperature at the well bottom reached 202.54 °C.

Thermo-elasto-hydrodynamic analysis of triangular textured mechanical face seals

A 3D thermo-elasto-hydrodynamic (TEHD) model is presented to study the effects of triangular dimples on the loadcarrying capacity, leakage and friction of a mechanical seal operated under mixed or full film lubrication conditions. The model is solved by the finite element method (FEM), which takes into account the effects of the Jakobsson-Floberg-Olsson (JFO) cavitation boundary condition, surface roughness, elastic-plastic contact, thermo-elastic deformation, and the temperature-viscosity relation. The numerical results of the TEHD model are quite different from those of the hydrodynamic (HD) and thermo-hydrodynamic (THD) models, especially at high speeds. In order to obtain the optimum shape and distribution of the triangular dimples, a comparative study is conducted to investigate different distributions of equilateral triangles and isosceles right triangles. The results show that a surface textured mechanical seal with isosceles right triangular dimples has the most significant hydrodynamic and pumping effects which, in turn, are beneficial to sealing face opening behavior and leakage limitation. The theoretical results are in good agreement with the experimental ones, and offer new guidance for the future design and development of high-speed mechanical seals for aviation piston pumps.

Contact status between seal ring and its support: crucial factor in hydrostatic mechanical face seal

PurposeThis paper aims to investigate the influence of the contact status between the seal ring and its support on the seal performance in hydrostatic mechanical face seal.Design/methodology/approachA thermal fluid-solid interaction (TFSI) model of hydrostatic mechanical face seal is further developed, in which the multi-body contacts between components are particularly given more attention. The numerical models of the flow field and complete seal assemblies are developed. A specific energy equation is obtained to simplify the calculation of film temperature. Based on the mechanism for the continuity condition of the physical quantities at the fluid–solid interface, the TFSI model uses an on-line iterative coupling method.FindingsThe contact status between seal ring and its support affects the seal performance significantly. The rotating ring and the stationary ring contribute differently because of the contact status difference.Originality/valueThe contact status between the seal ring and the ring seat is key to gain an insight into the performance of the hydrostatic mechanical face seal thus provides guidance for mechanical seal design.

Integrated Influence of Sliding Velocity, Outlet Pressure, and Seal Clearance on Optimum Dimple Area Density for Mechanical Seal

It is well known that the dimple area density is a key parameter for the design of mechanical seal with dimples. In the present paper, the integrated influence of sliding velocity, outlet pressure, and seal clearance on optimum dimple area density, represented by dimple number along the dimple column taken from the seal surface, are conducted theoretically by solving Reynolds equation, where the Floberg–Jakobsson–Olsson cavitation theory is implemented using a mass-conservative algorithm to accurately predict the behavior of cavitation. The results show that the optimum dimple area density is closely related to the operation parameters and the influence of each operation parameter can be divided into three regions. Moreover, for each operation parameter, both of the range of the divided regions and the corresponding values of the optimum dimple area density are strongly associated with the other two operation parameters. In addition, the influences of operation parameters on optimum dimple area density can be investigated by their effects on the maximum pressure caused by dimples.

A leakage channel model for sealing interface of mechanical face seals based on percolation theory

Abstract Leakage channels of contact mechanical face seals have significant influence on sealing performance. The porosity of initial sealing interface is obtained based on the fractal parameters of rotating and stationary rings firstly. The effects of fractal parameters, material properties and face pressure on porosity of sealing interface are revealed, and then the percolation assumption for single grid model of sealing interface is proposed. Finally, a leakage channel model based on the volume porosity of sealing interface is established and investigated accordingly. The proposed research is expected to provide the basis for the explanation of leakage and optimum design of contact mechanical face seals.

Characterization of Mechanical Seal using Hybrid of Natural Materials

Objectives: The aim of this research is to design and analysis of natural fibre mechanical seal using hybrid of Agave sisalana fibre and natural rubber as reiforcement and bio epoxy resin as matrix material. Methods/Analysis: The fabrication of the mechanical seal will involve internal mixing which is to mix up the waste tires with the Agave sisalana and hot pressing is to press or sinter the material into mechanical seal. The testing involved in this project is Tensile Test, Hardness Test, Absorption Test and last is Thickness Swelling Test. The result and data collected will be analysing by using graphs. Apart from that, ANSYS has been used to providing solid modelling and analysis on mechanical seal and mould. Findings: Fibre exhibits a very good reinforcement by increasing the mechanical properties in polymer but at certain amount it can change the properties of the composites. The best composition is 85% natural rubber+5% Agave sisalana fibre+10% Bio Epoxy Resin. Application/Improvement: With the growth of the industrial sector, mechanical seal will become one of the most important things in the piping industrial. By converting natural rubber into mechanical seal, it gives advantages to both parties. Embedding with Agave sisalana increases the mechanical strength of the natural rubber material.