| With the increase of rotating speed of rotating equipment,higher requirements are put forward for bearings and their lubrication and cooling methods.At high rotational speed,the lubricating oil is dispersed into oil droplets with different particle sizes,and distributed in the gas-phase space in the bearing chamber.The oil droplets and air are mixed,and form a gas-liquid miscible fluid.The lubrication methods bring the sealing problem of gas-liquid miscible fluid.However,there is no seal with the advantages of simple structure,high reliability,long service life and can effectively seal the gas-liquid miscible fluid.Therefore,it is of great practical and strategic significance to develop such a seal and realize its engineering application.A new type of noncontacting mechanical seal,gas-liquid miscible hydrodynamic mechanical seal(G-LMHMS),is proposed.In this paper,the steady-state characteristics,dynamic characteristics,and tribological properties of G-LMHMS were studied systematically and deeply by combining theoretical analysis and experimental research.And the theory and method of G-LMHMS is obtained,which provides a theoretical basis for engineering application.The working conditions of high-speed bearing chamber are complex.In order to obtain accurate sealing performance,it is necessary to study an analysis method that is suitable for miscible fluids and considers the interaction of multiphysics.The equivalent physical properties of gas-liquid miscible fluid were characterized by liquid volume ratio,and Reynolds equation of gas-liquid miscible fluid was established.The influence of temperature on fluid physical properties was considered,and the energy equation of gas-liquid miscible fluid was obtained.Combined with the heat balance equation and deformation coordination equation of the rotating ring and the stationary ring,the interaction relationships among the pressure,temperature and deformation were established,and the fluid-solid-thermal fully coupled analysis model of GLMHMS was formed.The coupling model was solved by finite element method and verified by literature and experiments,providing a theoretical basis for the performance calculation of G-LMHMS.The influence of rotational speed and pressure on sealing performance was studied.The change process of fluid micro-flow in the fluid film was analyzed from pressure distribution,streamline and steady-state characteristics.And the sealing mechanism of G-LMHMS was revealed.Depending on the strong shear flow effect brought by high rotational speed to counteract the pressure difference,G-LMHMS realized the sealing of gas-liquid miscible fluid in the bearing chamber.The effects of gas-liquid miscible fluid and gas on sealing performance were compared and analyzed,and the mechanism of gas-liquid miscible fluid was summarized.Due to the higher viscosity and density,the gasliquid miscible fluid makes G-LMHMS has a stronger dynamic pressure effect,resulting in the reduction of total leakage rate,the reduction of film stiffness,and the increasement of power consumption.The evolution process of sealing performance was analyzed under two states of low speed leakage and high speed reverse suction.The influence of typical structural parameters on the sealing performance was obtained.The optimal range of structural parameters was given,providing the guidance for the design and optimization of G-LMHMS structure.Based on the small disturbance method,and considering the influence of disturbance on the physical properties of gas-liquid miscible fluid,the dynamic Reynolds equation of gas-liquid miscible fluid was derived.Combined with the fluid-solid-thermal coupling model,the dynamic characteristic parameters were solved by finite element method.The influence of gas-liquid miscible fluid and gas on the dynamic characteristics was compared and analyzed.The mechanism of gas-liquid miscible fluid was revealed,and the corresponding relationship between the change of the fluid and the evolution of dynamic characteristics was obtained.The optimum range of structural parameters was acquired from the dynamic characteristics.The kinematic model of G-LMHMS was established,based on the dynamic characteristic parameters,and the motion of the stationary ring was obtained.The influence of the fluid and the physical properties on the following performance was studied.The optimal range of system mechanical performance parameters was obtained,providing the theoretical guidance for the overall optimization of G-LMHMS.According to the working environment of the seal,a high-speed GLMHMS tester with bearing lubrication was built.The sealing performance of G-LMHMS was tested under static and working conditions.The test results verified the excellent performance of G-LMHMS and the correctness and accuracy of the numerical model.According to the change process of leakage rate and temperature,the running process of G-LMHMS was divided into three stages:not open,not fully open and fully open,and the working characteristics were different.In the fully open stage,G-LMHMS can achieve a stable liquid sealing effect.Aiming at the friction and wear problems in the start-up process of GLMHMS,the tribological properties of the friction pair material were studied on a standard ring-on-ring friction tester.According to the working environment of the G-LMHMS and the characteristics of the start-up processes,four kinds of lubrication conditions with different amounts of lubricating oil are designed herein:dry friction,starved lubrication,oil-mist lubrication and oil lubrication.The test method of steadily increasing the rotational speed with a constant load is adopted to simulate the start-up process.The tribological properties of the friction pair material were analyzed by friction coefficient,friction temperature and micromorphology.The results showed that gas-liquid miscible fluid in the working environment of G-LMHMS can effectively improve the lubrication conditions.The spiral groove on the surface of G-LMHMS can reduce the contact force of the friction pair through the hydrodynamic effect,which can effectively reduce the COF of a friction pair.Compared with the effect of spiral groove,the friction reducing effect of the hard coating is more important.The friction reduction mechanism of friction pair under different lubrication conditions was revealed.The applicable range of different friction pair materials was obtained,providing the theoretical guidance for the G-LMHMS material selection.This paper presents a theoretical method of G-LMHMS,which provides a theoretical basis for the performance calculation and the structure optimization.The sealing performance of G-LMHMS in the whole running process were studied systematically and deeply by combining theoretical analysis and experimental research.This work can provide guidance for engineering application,promotion and optimization design of G-LMHMS... |
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