Study On Thermo-Hydrodynamic Lubrication Characteristics Of Spiral Groove Gas Face Seals Operating At Low Or Medium Pressure

With the expanding application of gas seal face,the thermal hydrodynamic effect and face distortion caused by the flowing of sealing gas,have been obvious.Face distortion caused by gas film temperature gradient,makes the seal faces contact and wear,which will even lead to the failure of the rotational equipment.A higher standard in the stability and reliability of gas face seal design is required.To obtain the mechanism of face distortion in gas face seal,spiral groove is chosed and the thermo-hydrodynamic characteristics operating at low pressure conditions are studied.The main contents and results of this dissertation are listed as follows,Firstly,the gas thermal hydrodynamic lubrication theoretical model was built based on the gas properties and gas thermal hydrodynamic lubrication theory,and the gas-solid-thermal coupling analysis method was applied to obtain the relationship of gas temperature distribution and face distortion.In this model,the influence of the gas viscosity,gas choked flow effect,surface structures and the thermal distortion on the sealing performances were discussed.The pressure boundary conditions,temperature boundary conditions and the restraint conditions of deformation were determined.Secondly,the isothermal lubrication sealing performance was obtained with the gas viscosity effect and choked flow effect considered,the gas film pressure distribution and the stream field were given,the sealing performance was analysis under different operating conditions and finally the optimized value of geometrical parameters of spiral groove were obtained.The results presented that the viscosity effect could be ignored until the sealing pressure larger than 3MPa.The choked flow effect would lead to the increase of sealing pressure in the inner diameter of seal face and the decrease of sealing pressure in the outer diameter of seal face,which is much obvious under the sealing pressure larger than 2MPa and the sealing clearance larger than 3μm.Thirdly,the influence of thermal effect and face distortion was discussed.The pressure distribution and temperature distribution of gas film under different sealing pressure and rotational speed was analyzed.And then the sealing performance was studied under the condition with and without thermal deformation considered.It was found that thermal distortion was mainly caused by the gas expansion resulted from the gas pressure and temperature decrease along the radius direction.With the increasing of sealing pressure and sealing clearance,the expansion rate increase and the gas film temperature decrease clearly in the outer side of seal face,which finally led to increase of the distortion value.The face distortion finally led to the decrease of opening force and the increase of leakage.The sealing pressure and sealing clearance played an important role in the temperature variation of gas film compared with the rotation speed.With the sealing clearance 3.5μm,sealing pressure 2MPa,and sealing rotational speed 20000r/min,the opening force decreased about 9% and the leakage ratio increased 100% with thermal deformation considered.Finally,a sealing test was built to experiment the temperature of seal face and the leakage of gas face seal under low sealing pressure condition.The results under static pressure conditions shown that the temperature decreased from the outside to the inside diameters,the temperature value decreased with the increasing of sealing pressure and the testing time.The experiment results under a certain rotational speed presented that the temperature increased with the increase of rotational speed.And the temperature increased gradually and finally tended to be stable with the increase of running time,while the leakage decreased gradually and finally tended to be stable.According to the studies,the gas thermal hydrodynamic lubrication performance of spiral groove gas face seal operation at low or medium pressure are obtained,a systematic study of the influence of operation parameters on the sealing performance are presented.The results can provide a reference for the further design of gas face seal in engineering application.