Dry Gas Seal Research Articles

Experimental and theoretical investigations on dry gas seal transient performance and its disparity with steady performance

Through high-speed dry gas seal test rig, the real-time film thickness and leakage rate of spiral grooved dry gas seal have been monitored under different closing forces which are changed by adjusting spring compression. Under the conditions of different spring pressures and seal face deflection rates, the change rules of transient opening force and leakage rate are obtained by solving the transient-state Reynolds equation based on the measured real-time film thickness. Meanwhile, the steady opening force and leakage rate are figured out by solving the steady-state Reynolds equation using the average value of the real-time film thickness. Results show that the variation trends of calculated results based on steady-state or transient-state theory coincide well with experimental results. But with the influence of nonlinear effect, the average value of transient opening force and leakage rate are larger than steady opening force and leakage rate calculated with the average value of real-time film thickness, and compared with the value of steady leakage rate, the average value of transient leakage rate considered seal face deflection is closer to the experimental monitoring results.

The influence of 3-DOF film thickness disturbance on transient performance of typical spiral groove dry gas seals

PurposeThe purpose of this paper is to investigate the influence rule and mechanism of three degrees of freedom film thickness disturbance on the transient performance of spiral groove, upstream pumping spiral groove dry gas seal (UP-SDGS) and double-row spiral groove dry gas seal (DR-SDGS).Design/methodology/approachThe transient performance of spiral groove, UP-SDGS and DR-SDGS are obtained by solving the transient Reynolds equation under different axial and angular disturbance coefficients. The transient and steady performance of the above-mentioned DGSs are compared and analyzed.FindingsThe film thickness disturbance has a remarkable impact on the sealing performance of DGS with different structures and the calculation deviations of the leakage rate of the UP-DGS will increase significantly if the film thickness disturbance is ignored. The axial and angular disturbance jointly affect the film thickness distribution of DGS, but there is no significant interaction between them on the transient sealing performance.Originality/valueThe influence mechanism of axial disturbance and angular disturbance on the transient performance of typical SDGSs behavior has been explained by theory. Considering small and large disturbance, the interaction between axial disturbance and angular disturbance on the transient performance have been studied.

Predictions of the thermo elastic deformation of dry gas seal rings in the hydrodynamic lubrication regime

Dry gas seals represent a significant advancement in turbo machinery due to their ability to handle high pressures and speeds without the use of external sealing fluids, such as oil or water, thus reducing contamination and increasing reliability. Despite their widespread use, internal working mechanisms are not fully understood to date, in particular regarding fluid film thickness prediction, which is an essential component of the seal design. The axial deflection of the rotating and stationary rings in a dry gas seal affects the development of the fluid film formed between the ring faces of the seal, influencing the performance of the seal during its operation, as well as leakage of the seal when it is at rest. The hydrodynamic and hydrostatic pressure fields of the fluid film, together with temperature gradients in the rings, induce axial deflection of these components. This in turn modifies the pressure field developed in the film. This paper focuses on establishing a methodology to couple the deformation field and the dynamic behavior of the fluid film (pressure and temperature fields) through numerical computations. Analytical relationships are employed to obtain the thermo-elastic deflection of the seal rings in the axial direction and this distortion is used in the numerical methodology to accelerate the prediction of the seal behavior. The coupled seal ring-fluid film dynamic system with 11° and 15° spiral angle is stable because the axial deflection calculated from numerical analysis produces a converging radial taper in the direction of the flow (producing a net opening force). An important result of this work is that the predicted magnitude of the axial deflection (as a result of pressure and temperature effects) under thermal and pressure loads on the stationary and rotating rings is smaller but of the same order of magnitude as the fluid film thickness.

Research on the Operational Modal Prediction of Dry Gas Seal System Based on Response Surface Method

The cross power spectrum function is used to realize the operational modal analysis and identification of the dry gas seal device system through the multi-reference point least squares complex frequency domain method. The steady state diagram and mathematical indicators MAC, MPD, MPC, MOV and MIF are used to verify the modal results. At the same time, based on the response surface method, with two different operating conditions of medium pressure and rotating speed, modal direction and modal order as the response surface variables, a time-varying modal recognition model is established. Through the Full Factorial experiment design, Box-Behnken experiment design and Central Composite experiment design, the suitable variable sample points are formed. A complete quadratic polynomial response surface model of the system operational modal parameters is established. The complex correlation coefficient, the modified complex correlation coefficient and the root mean square error are used to verify the effectiveness of the response surface model. It provides new method and technical support for realizing time-varying modal identification in this paper.

Gas-liquid separation performance of a micro axial flow cyclone separator

A micro two-stage axial flow cyclone was developed with guide vane in series in front of the dry gas seal filter to pre-separate the liquid and solid. The effects of vane blade outlet angle and wrap angle on the performance were verified by experiments, and then two-stage axial cyclones were optimized. Furthermore, the optimized two-stage axial flow cyclone was applied to the dry gas seal system of high-pressure natural gas compressor, and the performance was tested under 7.21–7.80 MPa. The results show that the vane blade outlet angle of the second stage is smaller than that of the first stage, while the vane blade wrap angle is larger. The two-stage cyclone can separate smaller droplets, and the separation efficiency increases by 10%. Under the high-pressure conditions, the separation efficiencies of the cyclone are more than 65%, and the cumulative efficiency of 1.5 μm droplet is more than 90%.

Theoretical analysis and experiment on gas film stiffness with slip flow in a spiral-grooved dry gas seal

Purpose This study aims to study the gas film stiffness of the spiral groove dry gas seal. Design/methodology/approach The present study represents the first attempt to calculate gas film stiffness in consideration of the slipping effect by using the new test technology for dry gas seals. First, a theoretical model of modified generalized Reynolds equation is derived with slipping effect of a micro gap for spiral groove gas seal. Second, the test technology examines micro-scale gas film vibration and stationary ring vibration to determine gas film stiffness by establishing a dynamic test system. Findings An optimum value of the spiral angle and groove depth for improved gas film stiffness is clearly seen: the spiral angle is 1.34 rad (76.8º) and the groove depth is 1 × 10–5 m. Moreover, it can be observed that optimal structural parameters can obtain higher gas film stiffness in the experiment. The average error between experiment and theory is less than 20%. Originality/value The present study represents the first attempt to calculate gas film stiffness in consideration of the slipping effect by using the new test technology for dry gas seals.

Effects of the inclination angles of DLC end face micro-texture on the tribological properties of dry gas seal rings

To improve the tribological performance of the seal rings in the dry gas seal, the elliptical micro-textures with different inclination angles (0°, 45°, 90°, 135°) were processed on the end face of SiC static rings by nanosecond laser. Diamond-like carbon (DLC) films were then deposited on the micro-textured end face. Under dry friction condition, the end-face friction and wear test was conducted to simulate the actual working state of the dry gas seal at start-up phase. The effects of micro-texture inclination angles and DLC phase change on the tribological properties of seal rings were investigated. The possible friction reduction mechanism was analyzed. The results show that compared with the smooth surface, the elliptical micro-texture can effectively improve the tribological properties of DLC films. At the same time, the inclination angle of the elliptical micro-texture has a remarkable influence on the tribological properties. When the micro-texture inclination angle is 90°, the static ring sample has the best friction reduction and wear resistance performance. Compared with the untextured sample, the average friction coefficient is reduced by 46.15%. The wear reduction characteristics of the textured end face are mainly contributed to the capturing effect of the texture on wear particles.

The influence and a direct judgement method of the flow state in supercritical CO2 dry gas seal

The influence and a direct judgement method of the flow state in supercritical CO2 dry gas seal

Bidirectional Trapezoidal Versus Unidirectional Spiral Groove Performance in Dry Gas Seals

The gas film characteristics of bidirectional dry gas seals with trapezoidal grooves were studied by comparing with the traditional spiral grooved gas seals. The two-dimensional compressible Reynolds equation was solved by finite difference method. The typical performance parameters including gas film force, leakage, gas film stiffness, and torque were compared under different parametrical conditions. The pattern of trapezoidal grooves wasted part of groove area in bidirectional operation; though the grooves were designed by overlapping trapezoids to make up for the performance loss, the resulting decrease in gas film stiffness was notable. The resisting disturbance ability of trapezoidal grooved seals was poorer than that of spiral grooved seals, while the load-carrying capacity, sealing ability, and power consumption of trapezoidal grooved seals differed slightly from those of spiral grooved seals. The trapezoidal grooved seals are not recommended in unidirectional rotational compressors due to the decreasing stability.

Calculation and verification of flow field in supercritical carbon dioxide dry gas seal based on turbulent adiabatic flow model

The current work investigates the influence of turbulence effect and different flow processes on Supercritical-CO2 (S-CO2) dry gas seal performance by theoretical calculation and experimental testing. Variations in both rotational speed and pressure can cause changes in the flow state within the gas film. The flow in the gas film follows laminar flow at low rotational speed and low-pressure conditions. As the rotational speed and pressure increase, the flow in the gas film gradually transforms into turbulent flow, and the turbulence effect has a significant impact on the leakage rate. Compared with the isothermal flow, the flow of the gas film is closer to the adiabatic flow process. The operating parameters have different levels of influence on sealing performance.

Dynamic behavior and difference pressure control of difference pressure regulator for dry gas seals

As a result of the research work based on comprehensive numerical and experimental studies, an analytical method for predicting direct action gas difference pressure regulator (DPR) characteristics for dry gas seal (DGS) system allowing to build up from the possible mode of dynamic instability and to ensure the maintenance of required difference pressure for the overall operating range of compressor has been developed. The method of static and dynamic characteristics analysis of the regulator is based on solving equations of the mass flow rates and the forces acting on the slide valve balances, the single-mass dynamic model of the movable part and the mass flow rates balance in the upper and lower chambers with the use of the analytical methods of the automatic control theory (ACT). The experimental verifications of the single-seated and the double-seated DPR designs with the inlet pressures of 9.28, 6.98, 5.0, 3.2 MPa have been satisfactory agreed with the calculation results. So at difference pressure on a slide valve more than 2.4 MPa with constant external actions, a loss of stability of the movable part of the DPR may occur. The damping chamber with the laminar flow restrictor, at a suitable choice of its geometry, provides the necessary attenuation of the vibration process. The conductivity of the feeding channel has a significant influence on the static characteristics of the DPR. Under the condition of the inlet restrictor significant resistance, it is provided a rather narrow range of the variations for the difference pressure across the slide valve.

Cross-Scale Flow Field Analysis of Sealing Chamber and End Face Considering the CO2 Real Gas Effect

The dry gas seal (DGS) is a non-contacting, gas-lubricated mechanical face seal commonly used in rotating machinery. Traditional analyses of DGSs treat the end face as an independent factor by setting the end-face inlet as boundary conditions, but limited attention is focused on the sealing chamber of the DGS. Using the finite volume method and the shear stress transport (SST) k-ω model, the coupling between the millimeter-scale sealing chamber and the micrometer-scale end face are simulated with regard to the real gas effect of CO2. The three-dimensional distributions of velocity, pressure and temperature in the cross-scale flow field are investigated under different working conditions. Moreover, the boundary parameters of the end-face inlet are modified by response surface methodology with a central composite rotatable design. The results demonstrate that the real gas effect of CO2 leads to an increased total inlet flow. When the pressure reaches 10.3 MPa, the relative difference is 51.90% compared to ideal gas. Minor temperature and pressure changes occur in the sealing chamber when the dry gas seal is in operation. However, the inlet temperature of the end face Tf increases and the inlet pressure of the end face pf decreases. These research results provide a reliable reference for engineering practice.

Numerical investigation on the performance of impeller back seal configuration in a supercritical CO2 radial-inflow turbine

Radial-inflow turbine is a core component in supercritical CO2 (SCO2) Brayton cycle. The leakage from the nozzle outlet towards the impeller back brings a great challenge to the efficiency and security of the power system. In this paper, the labyrinth seal (LS) and dry gas seal (DGS) are arranged on the impeller back of a SCO2 radial-inflow turbine and the influence on the comprehensive performance is investigated. Results demonstrate that both LS and DGS configurations can significantly reduce leakage of the impeller back and DGS configuration performs better. Compared with the configuration without leakage, the power and efficiency of DGS configuration are only reduced by 0.27% and 0.35% respectively. The seal clearance and the inlet width have a greater effect on LS configuration. The thermo-mechanical seal deformation values of DGS configurations are all less than 8 μm, which verifies the feasibility. Finally, a novel combined seal configuration with both LS and DGS is proposed and excellent performance is achieved, providing a potential approach for the sealing problem of SCO2 radial-inflow turbine.

Frictional Vibration Performances of Dry Gas Seal Rings with DLC Film Textured Surface via Chaos Theory

In this study, the frictional properties of dry gas seal rings with a diamond-like carbon (DLC) film textured surface were investigated using a vertical universal friction and wear tester. The ensemble empirical mode decomposition (EEMD) method was applied to extract friction and vibration signals. In combination with chaos theory, analyses of the friction and wear of dry gas seal rings were performed under specific working conditions. The results show that the variation in friction vibration attractors and phase-point average distance is consistent with the change in the friction coefficient. The DLC film textured surface effectively improves the frictional properties of dry gas seals. The edges of the microtextured pits can cut debris, so the diameter of the debris becomes increasingly smaller. At the same time, the microtextured pits can also capture wear debris. The optimized dimple diameter and area density were 250 μm and 15%, respectively. In this case, the texture pit can catch almost all of the debris, but the friction vibration was not severe.

Pengembangan Model Gas Conditioning Unit dalam Sistem Seal Gas di Kompresor Sentrifugal: Studi Kasus Kerusakan Dry Gas Seal

Dry gas seal is an important component in the sealing system in centrifugal compressors. The gas seal supply that enters the dry gas seal must meet the specifications that have been determined based on API 692. However, on reality at the site dry gas seal damage often occurs, one of which is due to contamination from the gas seal supply that will enter the dry gas seal. The sulfur contamination in the corrosive process gas reduces the life and reliability of the dry gas seal. In addition, the selection of a gas conditioning unit model that is not quite right will result in the gas seal supply quality beyond the predetermined specifications. In this study, to obtain a good quality gas seal supply, development was carried out in the existing gas conditioning unit, upgrade seal gas strainer design using the duplex type and changing the type of strainer, changing the size of the gas filter seal from 0.3 micron to 0.1 micron and the use of coalescing. filter, repair seal gas heater and heat tracing installation on the seal gas piping, and finally replacement of seal gas booster components. The research method used is the study of literature from various references and previous studies, collecting data in the field and analyzing the findings using the PROACT method. From the analysis, it can be concluded that the development of the gas conditioning unit model in the gas seal system has a positive impact on the reliability of the dry gas seal in this centrifugal compressor.

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.

Experimental Study on the Performance of the Gas Centrifugal Seal with Continuous Injection and Discharge of Sealing Fluid

The centrifugal seal has the advantages of simple structure, long service life and the cost is far lower than the dry gas seal. But under high-speed gas conditions, the temperature of the sealing fluid rises too high and low sealing pressure. This paper studies the gas centrifugal seal with continuous injection and discharge of sealing fluid, establishes a numerical model, simulates the gas-liquid two-phase flow field and temperature field in the sealing chamber. Revealing the effects of the speed and the sealing fluid flux on the sealing performance by comparing the changes in the sealing fluid pressure, temperature, and sealing capacity under different operating conditions. And the reliability of its application to gas mechanical seals is verified through experiments. The results show that at high speeds, the pumping compression effect of the sealing fluid is enhanced, and the sealing capability is improved. Within a certain range, increasing the flux of the sealing fluid can effectively reduce the temperature and prevent the sealing fluid from vaporizing, the continuous injection and discharge structure has a significant effect.

Performance Analysis and Optimization of Internal Spiral Groove Dry Gas Seal Based on Fluid-solid-thermal Coupling Method

Internal spiral groove dry gas seal (ISGDGS) are used to seal special positions of rotating machinery. There is an urgent need to address the problems caused by contacting of rotating and static rings during high-speed rotation of ISGDGS. The main aim of this study is to investigate the influence of spiral groove structural parameters on ISGDGS sealing performance. Fluid-solid-thermal coupling method was used to analysis the relationship of sealing performance (opening force, leakage, friction power, and gas film stiffness) and spiral-groove structural parameters. The test analysis method is used to study the sealing performance under four different structural parameters, and the obtained trends are the same as the analysis results. According to the analysis results, the value range of structural parameters for optimal sealing performance is proposed This thesis has provided a deeper insight into the influence of the structural parameters of end face on the sealing performance, and provides a basis for its optimal design.

Improving operational equipments reliability with CFD analysis: case study of dry gas seal

Improving operational equipments reliability with CFD analysis: case study of dry gas seal

Experimental measurements of the thermo elastic behavior of a dry gas seal operating with logarithmic spiral grooves of 11° and 15°

This work shows the experimental thermo elastic behavior of the stationary ring of a dry gas seal with logarithmic spiral grooves of 15° (common commercial configuration) and 11° spiral (configuration evaluated to confirm analytical predictions developed on previous works), as well as the hydrodynamic pressure of the fluid film. The stationary ring temperature is obtained through an array of sensors embedded in the ring and the ring deformation, resulting from the thermal and mechanical load, is collected by two strain gages. The hydrodynamic pressure produced in the fluid film is measured using dynamic pressure sensors. Two novel instrumentation methods are defined to collect the ring deformation and the dynamic pressure of the seal. The results show that the seal with spiral grooves of 11° at low speed presents a temperature increment induced by the contact between the rings; this contact may induce the premature fault of the rings, so that the 11° spiral seal needs more speed than the spiral of 15° to enter a hydrodynamic lubrication regime. The experiments show that the stationary ring distortion is induced by the temperature gradient and by the hydrostatic and hydrodynamic pressure; however, the thermal distortion of the ring is dominant for the current experimental conditions. The ring’s axial distortion also affects the seal static and dynamic performance due to the modification of the hydrodynamic regime.