Yuming Wang

An Acoustic Emission Study on the Starting and Stopping Processes of a Dry Gas Seal for Pumps

The starting process and the stopping process of a double dry gas seal for pumps were investigated by acoustic emission (AE) testing. The characteristic frequency band of contact of the seal faces was distinguished from noises in three different comparative experiments. The root mean square (RMS) of the AE signals after band-pass filtering was determined to effectively reflect the contact condition of the seal faces. Based on the characteristics of the AE RMS, both the starting process and the stopping process could be divided into three periods, and a lift-off rotational speed and a touch-down rotational speed were defined. The lift-off speed varied non-monotonically with the inlet pressure. The lift-off speed was smallest at a certain pressure, which meant that at that speed the seal faces lift-off most easily. The behavior of the touch-down speed was similar to that of the lift-off speed, but was a little smaller than the latter. These results reveal the potential of AE technology for monitoring the contact condition of dry gas seals during the starting and stopping processes and may help in the design and operation of the dry gas seals.

Face Rub-Impact Monitoring of a Dry Gas Seal Using Acoustic Emission

Face rub-impact of a dry gas seal was investigated using acoustic emission (AE) technology. A force applicator was designed and mounted on the seal test rig to provide controlled misalignment and thus induce rub-impact of the seal faces. Two types of AE sensor were mounted at different positions on the seal. For the PICO AE sensor mounted directly on the seal ring, the root mean square (RMS) of the original AE signal was sensitive to face rub-impact of the seal. When force was applied, the AE RMS of the PICO sensor gave a distinct periodic waveform with a period consistent with the rotational period above an initial noise signal. The magnitude and shape of the waveform changed as the applied force increased. For the R15α AE sensor mounted on the housing of the seal, no obvious changes could be found from the RMS of the original AE signal synchronously obtained during loading. Two kinds of signal processing methods were tried to eliminate noise. After band-pass filtering, the RMS of the AE signals of the R15α sensor indicated face rub-impact when the misalignment was relatively large. The empirical mode decomposition method using masking signals was found to be more effective than band-pass filtering in eliminating the noise but took much more computational time. The results indicate that the AE technology is a potentially effective tool in monitoring and investigating face rub-impact of dry gas seals.

Fluid-solid Interaction Model for Hydraulic Reciprocating O-ring Seals

Elastohydrodynamic lubrication characteristics of hydraulic reciprocating seals have significant effects on sealing and tribology performances of hydraulic actuators, especially in high parameter hydraulic systems. Only elastic deformations of hydraulic reciprocating seals were discussed, and hydrodynamic effects were neglected in many studies. The physical process of the fluid-solid interaction effect did not be clearly presented in the existing fluid-solid interaction models for hydraulic reciprocating O-ring seals, and few of these models had been simultaneously validated through experiments. By exploring the physical process of the fluid-solid interaction effect of the hydraulic reciprocating O-ring seal, a numerical fluid-solid interaction model consisting of fluid lubrication, contact mechanics, asperity contact and elastic deformation analyses is constructed with an iterative procedure. With the SRV friction and wear tester, the experiments are performed to investigate the elastohydrodynamic lubrication characteristics of the O-ring seal. The regularity of the friction coefficient varying with the speed of reciprocating motion is obtained in the mixed lubrication condition. The experimental result is used to validate the fluid-solid interaction model. Based on the model, The elastohydrodynamic lubrication characteristics of the hydraulic reciprocating O-ring seal are presented respectively in the dry friction, mixed lubrication and full film lubrication conditions, including of the contact pressure, film thickness, friction coefficient, liquid film pressure and viscous shear stress in the sealing zone. The proposed numerical fluid-solid interaction model can be effectively used to analyze the operation characteristics of the hydraulic reciprocating O-ring seal, and can also be widely used to study other hydraulic reciprocating seals.

Parametric Study on a Wavy-Tilt-Dam Mechanical Face Seal in Reactor Coolant Pumps

The reliability of mechanical seals in reactor coolant pumps is essential for the safety of pressurized water nuclear power plants. A wavy-tilt-dam (WTD) mechanical face seal, characterized by a circumferential wave with a radial taper and seal dam on one of the seal faces, has proved to be effective in practice. A theoretical model is developed to study the mechanism of the WTD seal in this article. Then, the structural parameters such as wave amplitude, taper, dam radius, and the number of waves are studied for the WTD seal under different rotation speeds and seal pressures. The results show that the mechanism of the WTD seal is the combination of hydrodynamic and hydrostatic effects, which do not work simultaneously. During the period of start-up and shutdown, when the film thickness and the pressure differential are both small, the seal works as a hydrodynamic seal, whereas it is a nearly hydrostatic seal at the stable working condition. The waves on the seal face will obviously impair the hydrostatic effect before cavitation occurs in the fluid film. The optimal values of the structure are obtained by analyzing the numerical results under certain working conditions. In addition, the performance varies obviously with rotation speed and seal pressure.

On frictional performance of sintering materials used by mechanical seals in water

Purpose – It is aiming at finding tribology performance laws and mechanism of sintering materials, including new materials, which are popular or potential materials of mechanical seals working under water condition with different working parameters, involving load and sliding speed. Design/methodology/approach – Falex-1506 tribo-machine has been used. The upper sample is rotated against the stationary sample below. They are all rings. The samples are WNV2, sintered pressureless bonded; CHV1, graphite-added PLSiC; R, sintered reaction bonded; R2, graphite-added RBSiC, cemented carbide YN6 and graphite MSMG. Twenty kinds of hard/hard and soft/hard pairs were tested under water condition. Then, SEM was used to observe the sliding surface to explain their rubbing mechanism. Findings – Friction coefficients decrease with the load increasing under water lubrication due to water holding by small holes on their surface. But the friction coefficients have no change with the varying of velocity. The hard alloy/sint...

Three-Dimensional Flow–Heat Coupling Model of a Wavy-Tilt-Dam Mechanical Seal

A three-dimensional flow–heat coupling model of a wavy-tilt-dam (WTD) mechanical seal is established to study the heat transfer in both the fluid and the solid domains. The upwind scheme is used to ensure the convergence of the numerical calculation. The inlet temperature boundary condition is discussed and two modified inlet boundary condition methods are proposed to eliminate the noncontinuity of the film inlet temperature. The method where the temperature gradient in the radial direction is assumed constant gives more reasonable results than the method where the temperature is assumed to vary linearly along the film thickness direction. The results show that the highest temperature is located near the inlet due to the waves, which will cause a backflow along the converging spaces formed between the rotor and seal faces (convex segments of the wave) in the circumferential direction. The thermal deformation in the radial direction is larger than the deformation that is caused by waves in the circumferential direction. In addition the deformation will increase the taper, which will result in an increase in the minimum film thickness. A parametric study shows that the maximum temperature of the film will decrease as the wave number increases. The rotor speed and pressure difference will obviously affect the performance of the WTD seal.