Xudong Peng

Thermoelastohydrodynamic Behavior of Gas Spiral Groove Face Seals Operating at High Pressure and Speed

A numerical modeling of thermoelastohydrodynamic gas spiral groove face seal behavior is presented. Temperature fields of the fluid film and the seal rings are computed, as they are the elastic and thermal distortions of the rings. Numerical analysis is carried out on a gas spiral groove face seal taking into account of choked flow effect. Analysis results show that both elastic and thermal distortions induce strong influence on the geometry of the fluid film, forming obvious divergent clearance which leads to significant decrease of minimum equilibrium clearance, exceeding 50% in degree. Thermal distortion may induce the same influence degree as elastic distortion on the minimum equilibrium clearance in high pressure cases, but the rotation speed has no obvious influence on the minimum clearance when both elastic and thermal distortions are considered. The thermal distortion as well as elastic distortion should be concerned in high pressure analysis.

Modeling of Gas Thermal Effect Based on Energy Equipartition Principle

In the present article, a gas thermal effect is modeled based on the energy equipartition principle. Two new independent state equations for an ideal gas are developed that provide a new way to analyze thermal effects in gas lubrication. Furthermore, the energy equation is derived for gas lubrication and the analysis of thermal effects is carried out on a gas spiral thrust bearing and a gas hydrostatic journal bearing. The results show that gas temperature increases significantly in the lubricated region at high speed for both the thrust and hydrostatic journal bearings, and the thermal effect positively influences the load capacity of the thrust bearing. The gas expansion effect makes the gas temperature decrease in the hydrostatic journal bearing, and the gas temperature decreases with an increase in the inlet pressure.

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.

Pseudo-Nine-Point Finite Difference Method for Numerical Analysis of Lubrication

Contours of surface texture of contact faces are not always parallel to the directions of the axis in solving Reynolds equations with finite difference method, and this often induces significant pressure saw-tooth effect, which results in an unignored analysis error. In this paper, pseudo-nine-point finite difference, as a new finite difference method, is introduced to solve the lubrication numerical problem of pressure saw-tooth. Also, application is carried out in gas lubrication of hard disk systems to verify the validity of the new method. In analysis, pressure distributions and gas floating forces are calculated for two different types of sliders, and the astringency and efficiency of the new method is discussed. Numerical results show that the pseudo-nine-point finite difference method can restrain pressure saw-tooth evidently, and presents better astringency and efficiency than the traditional five-point finite difference method. With the increase in mesh density, pressure distribution and gas floating force trend to steady. Also, numerical values of the floating force agree well with the experimental ones.

Experimental Investigation of an Inclined Ellipse Dimpled Gas Face Seal

An inclined elliptical dimpled gas face seal was experimentally investigated in order to provide evidence for theoretical study. An experimental setup and theoretical model were developed to study the hydrodynamic effect of this gas seal. Then, opening and steady performance of the seal was measured under different rotational speed and seal pressure. The clearance and leakage rate are discussed for different cases of pressure and rotational speed. The results showed that there was a good correlation between theory and experiment. Both the clearance and the leakage rate increased significantly with increasing rotational speed and seal pressure. The inclined elliptical dimpled gas face seal was a type of hydrodynamic seal.

Antiwear Properties of Bonded MoS2 Solid Lubricant Coating under Dual-Rotary Fretting Conditions

ABSTRACT Bonded MoS2 solid lubricant coatings are widely used in tribology for their friction-reducing and antiwear properties. However, such coatings have been rarely investigated in complex fretting conditions, such as dual-rotary fretting (DRF). DRF is a complex fretting wear mode that combines torsional fretting with rotational fretting. In this work, the antiwear properties of bonded MoS2 solid lubricant coating under dual-rotary fretting conditions were studied. Results indicated that the MoS2 coating had better friction-reducing and antiwear properties than the substrate for alleviating DRF wear. The coating can greatly influence the fretting regimes and reduce the coefficient of friction. Furthermore, the service life of the coating was strongly dependent on the competition of the two fretting components and was reduced as the rotational fretting component increased.

Thermohydrodynamic analysis on herringbone-grooved mechanical face seals with a quasi-3D model

A quasi-3D thermohydrodynamic model was introduced to analyze the seal performance of a herringbone-grooved mechanical face seal. In the model, the heat conduction equations of the seal rings and the energy equation of the lubrication film were solved simultaneously by the streamline upwind/Petrov–Galerkin finite element method. The Reynolds equation and the temperature equations were iteratively solved to obtain the liquid film pressure and the temperature distribution. A parameterized study was conducted to analyze the influence of the herringbone grooves’ geometry on the opening force, leakage rate, friction coefficient, and temperature rise. The results show that the hydrodynamic analysis overestimates the opening force because the viscous heat reduces the dynamic viscosity. The longer and narrower inner spiral groove gives the smaller leakage rate and the longer outer spiral groove with a smaller spiral angle shows the larger opening force.