Face Seal Research Articles

Parameter study and shape optimisation of a generalised ellipse dimple‐textured face seal

AbstractA new type of generalised ellipse dimple has been introduced to improve load‐carrying capacity (LCC) of gas face seal. Theoretical model was developed to study the influence of key geometrical parameters of generalised ellipse dimple texture on LCC and leakage rate of gas face seal. Then the optimised shape of dimples for maximum LCC under different working conditions were obtained using genetic algorithm method. It is observed that generalised ellipse dimple with proper unit number and long axis included angle can enhance LCC and make a better balance between LCC and sealing characteristics of gas face seal compared with conventional ellipse or circle dimple at high speed. Dimple‐textured gas face seal with multirow radial dimples outperforms that with single‐row radial dimple on sealing characteristics.

Paediatric in vitro models showed significant variations in fluticasone proprionate output from valved holding chambers.

We compared potential differences in drug delivery between different valved holding chambers (VHCs) used by asthma patients, with and without facemasks. An in vitro study design was created using a fluticasone propionate (FP) pressurised metered dose inhaler (pMDI) connected to a VHC. VHCs without facemasks and with sealed and unsealed facemasks were placed against face models that mimicked the features of a 1-year-old infant and a 4-year-old child. We analysed the amount of FP deposited on the filter in the face model after five breaths with a tidal volume of 75mL. Our measurements showed significant differences in the amounts of FP deposited on the filters, even without facemasks. The amount of FP delivered through the VHC and facemask combinations differed significantly, depending on the degree of the lack of facemask to face seal. All the tested VHCs showed significantly better drug output without a facemask. The VHC and facemasks chosen had a considerable and significant impact on FP delivery. The facemask seal should be checked whenever a VHC facemask combination is used. Young children should be taught to use the VHC mouthpiece as early as possible to optimise FP delivery and achieve more effective asthma therapy.

Study on the friction and wear performance of the micro-surface textured face seal under the water-lubricated conditions

Due to the poor lubricated performance of the low-viscosity lubricants (such as liquid oxygen and liquid hydrogen), the severe friction and wear of the seal’s pair for the high-speed turbopump in the cryogenic liquid rocket engine often occur, which may lead to the seal failure (excessive leakage or serious wear). For improving the tribological properties of the seal, the seal’s rotor with the micro-surface texture is proposed and the friction and wear performance of the seal pairs are studied. First, the theoretical model for solving the performance of the micro-surface textured face seal is developed. Second, the optimized structural parameters (dimple diameter, grooved area ratio and the dimple depth–diameter ratio) for the micro-surface texture are obtained, and the laser surface texturing method is applied to make the samples of the rotor. Third, the tribological properties of the micro-surface textured sealing ring are tested by the pin-disk tribology tester, and the comparisons between the friction coefficients and wear rate of the textured rotor ring and that of the ordinary steel disk and disk with the DLC coating are finished. The results show that optimized dimple diameter, grooved area ratio and the dimple depth–diameter ratio are 50 μm, 0.6 and 1, respectively, and the friction coefficients of the proposed rotor are 0.17 and 0.36, respectively, under the dry friction and water-lubricated conditions. The study is of great theoretical and experimental reference for designing the face seal under the low-temperature, low-viscosity and high-speed conditions in the cryogenic liquid rocket engine.

Comparing mask fit and usability of traditional and nanofibre N95 filtering facepiece respirators before and after nursing procedures

The reliability of N95 filtering facepiece respirators (FFRs) depends on correct fitting. The perceived usability of FFRs is equally important because discomfort during usage may affect compliance. Body movements during nursing procedures may also increase the risk of face seal leakage. To evaluate the mask fit and usability of the best-fitting 3M N95 FFR and the nanofibre N95 FFR before and after nursing procedures. The physical properties of these FFRs were also examined. This experimental study had a one-group multiple comparison design. In total, 104 nursing students participated, and performed nursing procedures for 10 min when wearing the best-fitting 3M FFR and the nanofibre FFR. Mask fit and perceived usability of the FFRs were evaluated. More participants failed to obtain a fit factor ≥100 when using the best-fitting 3M FFR than when wearing the nanofibre FFR (33.7% vs 21.2%) after the procedures (P=0.417). The nanofibre FFR also demonstrated higher usability than the 3M FFRs in terms of facial heat, breathability, facial pressure, speech intelligibility, itchiness, difficulty of maintaining the mask in place, and comfort level (P<0.001). The nanofibre FFR was also lighter, thinner and had slightly higher bacterial filtration efficiency than the 3M FFRs. The nanofibre FFR demonstrated significantly better usability than the 3M FFRs. None of the respirators were able to provide consistent protection for the wearer, as detected by face seal leakage after performing nursing procedures. Further improvement in the prototype design is needed to increase compliance and ensure the respiratory protection of users.

Hydrodynamic effect of non-closed elliptical grooves of bi-directional rotation gas face seals

PurposeThe purpose of this paper is to improve opening performance of bi-directional rotation gas face seals by investigating the hydrodynamic effect of non-closed elliptical grooves.Design/methodology/approachA model of non-closed elliptical groove bi-directional rotation gas face seal is developed. The distribution of lubricating film pressure is obtained by solving gas Reynolds equations with the finite difference method. The program iterates repeatedly until the convergence criterion on the opening force is satisfied, and the sealing performance is finally obtained.FindingsNon-closed elliptical groove presents much stronger hydrodynamic effect than the closed groove because of drop of the gas resistance flowing into grooves. Besides, the non-closed elliptical groove presents significant hydrodynamic effect under bi-directional rotation conditions, and an increase of over 40 per cent is obtained for the opening force at seal pressure 4.5 MPa, as same level as the unidirectional spiral groove gas seal. In the case of bi-directional rotation, the value of the inclination angle is recommended to set as 90° presenting a structure symmetry so as to keep best opening performance for both positive and reverse rotation.Originality/valueA model of non-closed elliptical groove bi-directional rotation gas face seal is established. The hydrodynamic mechanism of this gas seal is illustrated. Parametric investigation of inclination angle and integrity rate is presented for the non-closed elliptical groove bi-directional rotation gas face seal.

Experimental and numerical study of wavy mechanical face seals operating under pressure inversions

This paper investigates the impact of the face waviness and pressure inversions on the leakage and on the outer fluid entry of mechanical face seals using a numerical model and an experimental setup. The numerical model couples a transient Reynolds equation, an analytical contact model, a force balance solver, and a solver for the thermo-mechanical deformations. The experimental tests on a face seal with low waviness and on a face seal with high waviness provide leakage and outer fluid entry data, which are reproduced by the model. Contrary to the face seal with low waviness, the face seal with high waviness has poor performance and the pressure inversions increase significantly the ingression of outer fluid. The parametric study shows a decrease of leakage with increasing spring force, and an increase of leakage and outer fluid entry with increasing values of waviness amplitude. The higher leakage observed for wavy seals is shown to be due to the higher average film thickness, and to some extent due to the mechanisms associated with waviness: hydrodynamic pressure generation, film squeeze and stretching.

On the Sealability of Metal-to-Metal Seals With Application to Premium Casing and Tubing Connections

Summary Metal–to–metal seals are used in connections of casing and tubing in oil and gas wells. This paper describes the mechanisms of sealing metal–to–metal seals as investigated using an experimental setup and a stochastic numerical sealing model. Experiments were conducted for a variety of thread compounds and applied pin/box surface coatings. The results were used to validate a stochastic numerical sealing model for sealability. The model couples a contact–mechanics model with a flow model and takes into account the influence of all the surface–topography features by introducing the concept of seal permeability. Once validated, the model was used together with the experimental results to better understand the sealing mechanisms of metal–to–metal seals. The sealing configuration is a face seal with an 80–mm roundoff radius on one face pressing against a flat on the other face. The face–seal specimens were manufactured from P110 tubing to ensure material properties that are representative for casing or tubing. The test setup used is designed for investigating only the metal–to–metal seal of the connection. The setup can perform rotary sliding under constant load to simulate surface changes during makeup and subsequently perform a leakage test. The sealing limit is determined by applying 700–bar fluid pressure and then gradually reducing the normal force until leakage is observed. The data are subsequently used to validate the previously published stochastic numerical sealing model. The results indicate a strong dependence on the type of thread compound used for the onset of leakage. The thread compound affects the amount of wear and thus changes the surface topography of the interacting surfaces. It is shown that the stochastic numerical sealing model is capable of predicting the onset of leakage within the experimental accuracy. The model shows further that certain surface topographical features improve the sealing performance. In particular, a surface manufactured by turning on a lathe that is in contact with, for instance, a smooth shot–blasted surface topography leads to highly localized contact areas, which in turn yield the best sealing performance.

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.

Do Various Respirator Models Fit the Workers in the Norwegian Smelting Industry?

BackgroundRespirator fit testing is a method to assess if the respirator provides an adequate face seal for the worker.MethodsWorkers from four Norwegian smelters were invited to participate in the study, and 701 respirator fit tests were performed on 127 workers. Fourteen respirator models were included: one FFABE1P3 and 11 FFP3 respirator models produced in one size and two silicone half masks with P3 filters available in three sizes. The workers performed a quantitative fit test according to Health and Safety Executive 282/28 with 5–6 different respirator models, and they rated the respirators based on comfort. Predictors of overall fit factors were explored.ResultsThe pass rate for all fit tests was 62%, 56% for women, and 63% for men. The silicone respirators had the highest percentage of passed tests (92–100%). The pass rate for the FFP3 models varied from 19–89%, whereas the FFABE1P3 respirator had a pass rate of 36%. Five workers did not pass with any respirators, and 14 passed with all the respirators tested. Only 63% passed the test with the respirator they normally used. The mean comfort score on the scale from 1 to 5 was 3.2. The respirator model was the strongest predictor of the overall fit factor. The other predictors (age, sex, and comfort score) did not improve the fit of the model.ConclusionThere were large differences in how well the different respirator models fitted the Norwegian smelter workers. The results can be useful when choosing which respirators to include in respirator fit testing programs in similar populations.

Investigation of two-phase change flow in mechanical seal with complex solid surfaces

Phase change flows between seal faces play an important role in the performance of mechanical seals. Cavitation and boiling phenomena are observed to occur between mechanical seal faces. Most studies on phase change flows in mechanical seals focus on only one phenomenon. However, in different mechanical seal structures, for example, sector-groove seals, cavitation and boiling may appear simultaneously when the temperature and speed are changed. This study contributes to ongoing investigations in the field by proposing a phase change flow model considering both cavitation and boiling in mechanical seals. First, the governing equations and main features of the proposed model are discussed based on the mass conservation law, which is particularly useful in cases where both cavitation and boiling occur. Then, numerical schemes were constructed by employing the liquid volume fraction and analyzed by considering two different forms of fluid flux equations. Case studies of two models, namely, the wavy face seal and hydrostatic seal, were conducted and separately analyzed, and the numerical results demonstrated the feasibility of the proposed model. Then, numerical simulation and experiment of a sector-groove seal were conducted to demonstrate the advantage of the proposed model. The proposed model is especially effective for analyzing the two-phase flow field bounded by complex solid surfaces.

Assessment of respirator fit capability test criteria for full-facepiece air-purifying respirators

An ASTM International subcommittee on Respiratory Protection, F23.65 is currently developing a consensus standard for assessing respirator fit capability (RFC) criteria of half-facepiece air-purifying particulate respirators. The objective of this study was to evaluate if the test methods being developed for half-facepiece respirators can reasonably be applied to nonpowered full-facepiece–air-purifying respirators (FF–APR).Benchmark RFC test data were collected for three families of FF–APRs (a one-size-only family, a two-size family, and a three-size family). All respirators were equipped with P100 class particulate filters. Respirators were outfitted with a sampling probe to collect an in-mask particle concentration sample in the breathing zone of the wearer. Each of the six respirator facepieces was tested on the National Institute for Occupational Safety and Health 25-subject Bivariate Panel. The RFC test assessed face seal leakage using a PortaCount fit test. Subjects followed the corresponding Occupational Safety and Health Administration-accepted fit test protocol.Two donnings per subject/respirator model combination were performed. The panel passing rate (PPR) (number or percentage of subjects in the panel achieving acceptable fit on at least one of two donnings) was determined for each respirator family at specified fit factor passing levels of 500, 1,000, and 2,000. As a reasonable expectation based on a previous analysis of alpha and beta fit test errors for various panel sizes, the selected PPR benchmark for our study was >75%.At the fit factor passing level of 500 obtained on at least one of two donnings, the PPRs for three-, two-, and one-size families were 100, 79, and 88%, respectively. As the fit factor passing criterion increased from 500 to 1,000 or 2,000, PPRs followed a decreasing trend. Each of the three tested families of FF–APRs are capable of fitting ≥75% of the intended user population at the 500 fit factor passing level obtained on at least one of two donnings. The methods presented here can be used as a reference for standards development organizations considering developing RFC test requirements.

A thermo-elasto-hydrodynamic lubrication modeling approach to the operation of reactor coolant pump seals

In a nuclear power plant, the thermal energy from the reactor chamber is transported out to the steam generators through a fluid called reactor coolant. Pumps circulating the reactor coolant in a closed loop have a multistage sealing system including a controlled leakage face seal. It is crucial to understand and predict the performance of this mechanical seal to prevent exposure of this radioactive fluid to the environment. This paper introduces a novel modeling approach that allows fast and accurate prediction of the operation of an axisymmetric seal. Thermal and mechanical parameters governing the performance of the seal have been shown to match well with previous experiments. The new model allows investigation of yet unexplored process variables. • The results from the integrated TEHL model match well with published data. • Changes in the shaft speed are predicted to cause little variation in leak rate. • Thermal deformations cause the leak rate to increase linearly with taper angles. • Leak rate is impacted by the operational history through friction at the dynamic seal.

Sealing System Analysis of Rotary Piston Pump

Rotary piston pump is designed by the Wankel engine. The structure, working feature and sealing system of rotary piston pump are introduced. The mathematical model of the internal cylinder profile and the theoretical flow are obtained by analysing the structural characteristics of the new pump. The axial seal and face seal of the rotary piston pump and their structures are analysed. The force analysis of the sealing strip is carried out in various cases. It can be concluded from the analysis that, for axial sealing, the key parameters that affect seal strip wear are working pressure, rotate speed of the crankshaft and the friction coefficient between sealing strip and inner wall of the cylinder. For axial sealing, the force of the spring under the curved sealing strips, the size of the sealing rings and curved sealing strips and material of them are the key design parameters.

Friction performance of DLC film textured surface of high pressure dry gas sealing ring

After applying the diamond-like carbon (DLC) coating and surface micro-texturing into dry gas seal, the friction performance of textured surface DLC film of high pressure dry gas sealing ring has been researched in this paper. Firstly, the variation curves of friction coefficient with different load, rotation speed, and micro-texture geometric parameters are measured by using end-face friction and wear experiment machine (HDM20) under dry friction condition. Secondly, in order to compare the wear condition, the surface morphology of pretest and posttest is analyzed by using three-dimensional non-contact surface topography instrument (ST400). The experiment results show that: (1) The seal face which exists micro-textured DLC film has low friction coefficient, (2) under the same condition of micro-textured parameters, the friction coefficient would decrease with the increase in the load and would decrease firstly and then increase with the increase in the rotation speed, and (3) under the same running condition, the friction coefficient would decrease with the diameter of micro-pit and would increase with the increase in the density of textured area; however, the changing degree of friction coefficient would decrease. The experiment results could provide foundation for researching the tribological characteristics of faces of dry gas seal and optimizing the micro-textured structure.

Simulation Calculation of Temperature of the End Face for Mechanical Seals Based on Fractal Theory

In order to study the effects of operating parameters and surface topography on temperature of the end faces for mechanical seals, an average temperature calculation model of end faces for mechanical seals was established based on the contact fractal model and the friction factor fractal model, adopting fractal parameters to characterize surface topography, and simplifying the seal ring as equal cross-sectional equivalent cylinder. Influencing factors of average temperature were analyzed by simulation calculation for friction pair faces matched by cemented carbide YG8-carbon graphite M106K of partial balance mechanical seal. Theoretical calculation results show that the average temperature of seal face increased linearly with the increase of spring pressure or sealed fluid pressure, and increased approximately linearly with the increase of rotating speed. The average temperature increased with the increase of fractal dimension and with the decrease of characteristic length scale of the soft ring. The change of average temperature was smaller when the fractal dimension was smaller and the characteristic length scale was larger, while the average temperature increased rapidly when the fractal dimension was larger and the characteristic length scale was smaller.

Numerical modelling and comparison analysis of pressure distribution in the gas film for non-contacting face seals

The tightened-up norms concerning the emission of harmful substances into the natural environment are putting before designers of knots sealing very rigorous requirements. One should notice that mechanical seals are ones of most often applied sub-assemblies of the sealing nodes. The main task for mechanical seals is to maintain maximum tightness. They are applied practically in all branches of industry and must fulfil their function while working under various operating conditions. The determination of the pressure distribution in the fluid film layer is necessary to calculate the gasdynamic force and moments. A two-dimensional equation of Reynolds was solved based on Finite Volume Method (FVM). At the presented work findings of the simulation results concerning the comparison get based on the author's computer program in C++ language with results obtained from the commercial ANSYS CFX program was presented.

Use of hydrated material for dynamic seal faces in shaft seal

Use of hydrated material for dynamic seal faces in shaft seal

Suction effect of cavitation in the reverse-spiral-grooved mechanical face seals

Abstract Cavitation suction effect is investigated to control the leakage of the mechanical face seals. A face pattern including the forward, reverse spiral grooves and the annular groove is designed. The cavitation suction effect on the leakage and frictional torque are experimentally studied by a developed experimental setup and its mechanism is disclosed by a numerical model. The results show that the low pressure in the cavitation zone is the root of the suction effect and the cavitation is dependent upon the rotational speeds and loads. The zero leakage or reverse suction is achieved by the cavitation suction effect in a range of rotational speed for the fixed load. The cavitation effectively improves the tribological property of the mechanical seals.

Numerical modeling and analysis of the noncontacting impulse gas face seals

Noncontacting mechanical seals with various kinds of face surface modifications have established their position in the sealing technique. Over the last few years, a lot of works dedicated to the impact of various surface modifications on the dynamics of working rings have been created. This paper presents model studies regarding relatively unknown noncontacting impulse gas face seals. Here, a mathematical model of impulse gas face seals is developed including the nonlinear Reynolds equation and stator dynamics equations, which were solved simultaneously using numerical methods. An original computer software written in C + + language was developed. A number of numerical tests were conducted and the phenomena occurring in the radial gap during seal operation were analyzed. Final conclusions were drawn and several features were indicated characterizing impulse face seals. It should be emphasized that numerical research on this type of seals has not been published yet. The literature usually presents simplified models for the noncompressible medium, which can be solved with the use of analytical methods.

Tribo‐chemical smoothening process with silica nanoparticles

AbstractAdditional silica (silicon dioxide) nanoparticles were added in the tribo‐gap to prevent the severe abrasive wear. The method was a flat surface‐contact reciprocating sliding test between the sintered silicon carbide surfaces with water lubrication. Before testing, the silica nanoparticles were added in the tribo‐gap. These silica nanoparticles acted as a buffer layer during the initial running‐in, thus the abrasion risk was decreased. After running‐in, the silicon carbide surface was tribo‐chemically smoothened without severe abrasion. Comparing to the same tests without silica nanoparticles, the same ultra‐low friction state (friction coefficient was approx. 0.01) was built, and the running‐in period was shortened by 80 %. As has been well reported, the tribo‐chemical smoothening process for silicon carbide needs abundant water, e. g., in the point‐contact tests. However, in the surface‐contact case, water is locally insufficient, which induces severe wear. The preset silica nanoparticles can solve this wear problem. Therefore, it is not necessary to polish the silicon carbide surfaces as the seal faces in mechanical seals. Instead, a pair of rough silicon carbide surfaces can be pressed onto each other and then proceed to a running‐in with preset silica nanoparticles. After running‐in, a pair of precisely mated tribo‐chemically smoothened surfaces can be naturally obtained.