| The liquid film seal is a non-contacting mechanical seal with the advantage of small wear,long life,low energy consumption,stable working conditions and good adaptability,it has been widely used in petrochemical pumps,compressors and other rotating fluid machinery.However,in practical applications,due to the original engine steering or process errors and other reasons,it tend to cause the centrifuge pump and other equipment reverse rotation,so unidirectional groove seal can't produce dynamic open force and it could cause sealing failure,and even cause the shaft lock,device shutdown and other serious accidents.In 1993,The United States John Crane corporation introduced a bi-directional rotary fir-tree grooves dry gas seal which has a Symmetrical structure and could produce enough open force,and in practical applications,it had been a good sealing effect.However,the theoretical research on the liquid film sealing with positive and negative working ability is still rare.In this paper,the liquid film seal with fir-tree grooves is used as the research object,and the steady-state and dynamic characteristics of liquid film seal with fir-tree groove is systematically analyzed and numerically simulated.The experimental results show that the accuracy of the calculation program and the actual sealing performance of the liquid film seal with fir-tree grooves are good,and it could lay a good theoretical foundation for the further theoretical research and engineering application of the liquid film seal with fir-tree grooves.In this paper,the finite element program is used to solve the steady-state control equation of liquid film seal,and the pressure distribution is obtained.The influence of structure parameters and operating conditions on the steady-state characteristics such as open force,leakage rate and friction coefficient were analyzed.And the validity of the calculation program is verified by the experiment.The results show that the liquid film seal with fir-tree grooves can provide sufficient opening force to ensure the non-contact operation of the seal,speed,medium pressure,groove depth ratio and helix angle have great influence on the steady-state characteristics,but the impact of trough ratio is smaller.The dynamic characteristic analysis model of the liquid film seal with fir-tree grooves was established.Based on the small perturbation method of linearization,the differential equation of liquid film perturbation pressure is deduced in detail.The finite element method is used to solve the liquid film perturbation equation of the liquid film seal with fir-tree grooves,and the film stiffness and damping coefficient is obtained,The influence of speed and liquid film thickness and on stiffness and damping coefficient is analyzed,which provides theoretical support for further study on the dynamic performance of liquid film seal with fir-tree grooves.A dynamic analysis model of non-contacting liquid film seal is established,The nutation and precession of the static ring in the inertial reference coordinate system are analyzed.The vibration characteristics of single-degree-of-freedom axial motion and two-degree-of-freedom angular oscillations are analyzed respectively.The perturbation motion equation is numerically calculated by the perturbation method and the Runge-Kutta method.The influence of spring stiffness and static ring mass on the vibration characteristics of liquid film seal is studied.Through the above work,it is found that the liquid film pressure distribution there are two high-pressure areas,respectively,in the two fir-tree grooves at the root tip.The cross-interaction between axial perturbation and angular perturbation in the liquid film seal is very small and could be ignored.In the vibration response and stability analysis,the three-degree-of-freedom perturbation motion can be simplified to an axial perturbation motion and another perturbation motion that is angularly oscillating along the orthogonal axis.The liquid film seal with fir-tree grooves under the conditions of small disturbance,will be in the transient vibration to restore the equilibrium state,that is,with axial and angular stability. |
PDF Full Text Request