Study On The Dynamic Characteristics Of Diffused Self-pumping Hydrodynamic Mechanical Seals

Non-contact mechanical seals are complex and susceptible to many factors during operation.The research of non-contact mechanical seals involves the influence of fluid mechanics,tribology,contact theory,heat transfer,phase transition,vibration dynamics and other disciplines.At present,the mainstream research of non-contact mechanical seals mainly focuses on end face friction and wear,sealing performance and end face thermodynamic deformation.This thesis combines the basic related theoretical basis of mechanical seals,uses the knowledge of computational fluid dynamics and mechanical vibration,and adopts scientific research methods to study the diffused self-pumping hydrodynamic mechanical seal that can be applied to the seals of nuclear reactor coolant pumps,and its sealing performance and vibration characteristic response law under the condition of vibration interference.Firstly,the new sealing structure form of diffuse type in non-contact mechanical seal is introduced,and its structural characteristics and functions in the sealing system are explained.Secondly,considering the existence of the end liquid film,the three-dimensional modeling software was used for solid modeling,and the simulation analysis of the three-dimensional laminar flow model was carried out by relying on the simulation software to simulate the three-dimensional laminar flow model by using the knowledge of fluid mechanics.Thirdly,the sealing performance of the diffused self-pumping hydrostatic mechanical seal under various working conditions(structural parameters and operating parameters)was studied,and the kinetic parameters of vibration dynamics were further obtained,and the influence of liquid film thickness and number of grooves on the dynamic characteristics of liquid film was analyzed.Then,the axial seal vibration system was established,and the axial displacement in the system vibration process was calculated by using the superposition principle of small disturbance method,the simultaneous vibration equation and leakage rate calculation formula,and the response law under different vibration interference forms was dynamically analyzed by taking the leakage rate as the vibration response.Finally,the diffused self-pumping hydrostatic mechanical seal ring was processed,and the excitation generation device was used to test its sealing performance after vibration interference on the pump mechanical seal test platform.The main research results and conclusions are as follows:(1)The flow characteristics of the three-dimensional laminar flow model of the diffused mechanical seal are analyzed,and the calculation formulas of various evaluation indicators of the sealing performance are given,and the leakage rate,opening force,velocity vector perpendicular to the Z direction of the sealing end face and liquid film damping of the expanded mechanical seal are obtained under the determined structural parameters and operating parameters,which provides the necessary dynamic characteristic parameter data for further analysis of the vibration law of the sealing system.(2)The axial vibration model of the diffused self-pumping hydrodynamic mechanical seal was established.Considering the stiffness and damping of the auxiliary O-ring and the stiffness and damping of the liquid film between the end faces of the sealing ring,a sealing vibration system composed of static ring-liquid film-moving ring-elastic element was established,and the force situation was analyzed,and the dynamic equation system of the diffused self-pumping hydrostatic mechanical seal when disturbed by vibration was constructed in the form of matrix expression.(3)The superposition principle of small disturbance method is adopted,combined with the dynamic equation and leakage rate calculation formula based on Newmark-β method,and the leakage rate is used as the response of the sealing vibration system.The analysis shows that a positive leakage rate indicates a true leak in the sealing vibration system,and a negative value indicates that the sealing rings in the system are in contact with each other and collide.The sealing performance of the sealing vibration system under free attenuation vibration,self-excited vibration and smooth random ground disturbance under extreme conditions were considered.The results show that the size of the liquid film at the end of the sealing ring under the free attenuation vibration is within 1.6μm,and the sealing performance is still good even if the vibration interference is considered;the spindle rotation causes the end liquid film instability to produce the excitation form of self-excited vibration,which will significantly affect the sealing performance,and the spindle speed and initial amplitude need to be considered;the seal will fail under the smooth random ground motion interference of the class VII seismic intensity of the Class I site,and the greater the seismic intensity,the greater the response.(4)Use the laser marking machine to process the spiral groove and the expansion ring groove on the end face of the moving ring,weigh the quality of each component of the sealing vibration system,use the external excitation generation device composed of signal generator,power amplifier and exciter to carry out the sealing performance experiment under different pressure conditions,compare with the simulation calculation data to find that the leakage rate of the test is too large,analyze and give the reasons that may produce the test results,and lay a foundation for further improvement of the relevant experimental content.