Study On The Influences Of Cavitation Thermal Characteristics And Microscale Effect On Mechanical Seal Performance

The cavitation phenomenon in the liquid film of the liquid lubricated mechanical seal has a very important influence on the loading capacity of the liquid film.Since cavitation occurs generally at room temperature,the cavitation model is usually established under isothermal assumptions.Especially in the case of high rotational speed,due to fluid velocity varies and temperature rises caused by internal friction,the influences of cavitation on the sealing performance become more prominent.Moreover,the sealing lubrication performance is more complicated due to the microscale effect of the sealing micro film gap.Currently,the study of cavitation thermal characteristics and micro-scale effect of liquid lubricated mechanical seal is still being explored.Therefore,The relevant theoretical models are needed to establish to analyze the influence of cavitation thermal characteristics and micro-scale effect on on the sealing performance of the hydrodynamic lubricated mechanical seal,and providing a reference for further understanding of the failure mechanism and design of mechanical seal.This project is derived from the National Natural Science Foundation of China(Study on Internal Microscale Flow and Seal Lubrication Mechanism of Sealing Faces of Hydraulic Machinery)(Project Number: 51279067).The main research work and conclusions are as follows:(1)Taking the upstream pumping mechanical seal as an example,and on the basis of considering the relationship between the viscosity and temperature,the cavitation thermal characteristics model based on the mass transport equation was established by using the computational fluid dynamics method and the Fluent secondary development function(UDF).The influences of cavitation thermal characteristics on the performance of the upstream pumping mechanical seal were analyzed by comparing the commonly used viscosity-temperature effect model.The results show that the cavitation thermal characteristics at high rotational speed weakens the high pressure area forming ability,reduces the pumping rates and the opening force of the upstream pumping mechanical seal.Therefore,in the analysis of sealing failure mechanism,the influences of cavitation thermal characteristics should be considered.(2)Based on the theory of microscale effect,the importance of surface wettability to micro-flow and upstream pumping mechanical seal was expounded.Then,the apparent viscosity model for the hydrophilic sealing face and the boundary slip model for the hydrophobic sealing face were established respectively according to the difference of wetting performance,and the influences on the cavitation structure of liquid film and performance of mechanical seal was analyzed.The related research can provide some reference for the treatment and selection of the material properties of the liquid lubricated sealing ring in the actual operation.The results show that the shear stress is relatively small in the vicinity of the groove area and the cavitation area for the hydrophilic and hydrophobic sealing faces,and is relatively large in the dam area and the weir area.With the increase of the wettability of the sealing faces,the sealing opening force increases,the degree of cavitation in the sealing face deepened,and the shear stress in the sealing face increases.(3)Focusing on the problems that the opening force and stability of the water-lubricated mechanical seal are limited,the boundary slip micro-scale effect was considered,using artificial means in the sealing face to form a reasonable slip zone and non-slip zone,and based on the viscosity-temperature effect and cavitation thermal characteristics,the three-dimensional non-uniform slip model of the upstream pumping mechanical seal was established.the influence of different slip amount and rotating speed on the opening force,cavitation area,temperature field and leakage rate and other performance parameters of the seal was analyzed.The results show that it is an effective and feasible method to improve the sealing performance by increasing the slip amount by the surface treatment of the spiral groove,and the surface treatment layer is at the bottom of the spiral groove,which can avoid wear damage.