Study Of The Stability Of Bi-direction Rotaional T-groove Dry Gas Seal

The increasingly high parameterization of the industrial equipment makesstringent demands that the shaft seal has simple structure, long life,stableperformance and strong adaptability. Because of the characteristics of lowleakage,low consumption,long life, easy installation and the ability ofbi-direction rotation,T-groove dry gas seal becomes the mainstream of shaftsealing in rotating machinery.The dry gas seal includes unidirectional andbi-directional rotation according to the direction of rotation.The asymmetry ofthe groove structure makes the non-contact mechanical seal in unidirectionalrotation only work along the positive direction of rotation, but can not operate inthe opposite direction.In dry gas seals, the bi-directionally rotating T-groove drygas seal with symmetrical groove can prevent the rotating and stationary sealrings from the hard solid phase contact under the positive and negativerotation,which attracts more and more attention. The present thesis carries onthe research based on the stability of dry gas seal with T-grooves. The maincontents and results are as follows:In the thesis, the three stages of T-groove dry gas seal, such as startup,operation and shutdown, are selected to study the stability. The author verifiesthe technical route according to the combination of the theory, simulationcalculation and experimental study of dry gas seal, and also makes researchesand discussions on the parameters affecting the stability of the T-groove dry gasseal and how to improve this stability.Considering the rotation with dry friction occurring in the startup andshutdown influences the stability most, and it is the main reason that causes thepremature failure of dry gas seals. The main reason causing premature failure isthat the sealing pair runs for a long time at speed which is below the openingspeed for separating the sealing pair. Researching on the opening speed in thisstage benefits for achieving the computing opening speed in short time aspossible, so as to reduce the effect of dry friction on the stability. After avoidingpremature failure,the research on the stability is mainly manifested in thenormal operation stage, and it is necessary to make further analysis on thestability of this stage.In the dissertation, the fault tree analysis method is selected to analyze thedry gas seal system, obtaining that the main factors influencing the stability ofdry gas seal operation. And it is concluded that the influence weights of various parameters on the sealing performance for T-groove on the basis of simulationanalysis, and also the author defines the stability influencing parameters for thestable operation of dry gas seal: opening force, opening speed, gas filmstiffness, end face temperature, friction power consumption, the torque of theend face and the leakage.All of the related theoretical calculation, simulationand experimental research are carried around the stability parameters.In the simulation experiments, the groove optimization analysis for thebi-direction rotating T-groove is carried out based on the principle of theatmospheric film opening force and film stiffness helping to improve thestability of dry gas seal. The nondimensionalization of the Reynolds iscompleted through the Mesh-free method, in order to analyze and calculate thedynamic and static pressure, pressure distribution and carrying capacity of fluidflow of the T groove dry gas seal, from which the rule of pressure distributionfor flow field characteristics and the static pressure distribution of the seal facein the three dimensional view are received. Then the Fluent software is used tomake a large number of simulated optimal calculation for different typeparameters of the T-groove based on the pressure distribution law and maximumopening force. Furthermore, the optimized results of the groove are made acontrast analysis with the original groove shape in the end opening force, filmstiffness and leakage, which obtains a new type groove-OTG with a largeropening force and film stiffness.In this thesis, the nonlinear partial differential equation is transformed intothe linear partial differential based on the PH linear method to approximatelyobtain the analytical solution of gas dynamic pressure distribution for the Tgroove. It is concluded the formula of stability parameters, and the designscheme of this stage to avoid and reduce friction and wear of the structure isprovided. At the same time, with considering the influence of the axial smallperturbation and angular swing, the gas film stiffness expression of this time isset up, the characteristic curve of the stable operation for the dry gas seal ismapped, and the stability criterion of the operation for the dry gas seal waspresented.In terms of testing experimental parameters, the spindle speed, torque andface temperature and transverse pressure of the T-groove dry gas seal aremeasured in experiments. On one hand, the correctness of the simulation data isverified by comparing with these experiment results. On the other hand, thetorque, end face temperature and other parameters tested through the experimentcan determine the opening rotating speed. Meanwhile, the stability parameterrange is obtained by studying the stable sealing performance through externaldisturbance. The present research results can further improve the stability of bi-directional rotating mechanical seal system, and the dissertation provides the basis and reference for the further study and application of T-groove dry gas seals and also provides the necessary theoretical basis for the design and industrial application of dry gas seals.