Study On The Gas-liquid-solid Flow Characteristics And Seal Performance In Micro-gap Of Hydrodynamic Mechanical Seal

During the operation of the hydrodynamic mechanical seal,cavitation occurs when the partial pressure of the liquid film is lower than the saturation vaporization pressure due to the micro-shape of the end surface or the corrugation,etc.In addition,the imperfection of the sealing medium,the wear off of the end face occur,and negative pressure suction on the low pressure side often cause tiny liquid particles to entrain in the gap liquid film,resulting in gas-liquid-solid multiphase flow inside the seal gap.The presence of solid particles in the lubricating film will cause changes in the gap flow characteristics and the sealing performance,and in severe cases will cause the dynamic pressure tank to clog and lose its proper function.Therefore,the study of the gas-liquid-solid multiphase flow characteristics and its influence on the sealing performance of micro-gap is an important issue that has attracted much attention and remains to be studied in the field of hydrodynamic mechanical seal.In this paper,under the support of the National Natural Science Foundation of China(51279067),the hydrodynamic mechanical seal is taken as the research object,and a gas-liquid-solid multiphase flow calculation model involving cavitation and solid particles is established to study the gas-liquid-solid flow characteristics of micro-gap.And the effect on the seal lubrication performance,provides a theoretical basis for the design of high-performance hydrodynamic mechanical seal,the main research work and conclusions are as follows:1.Taking the upstream pumping mechanical seal as an example,a gas-liquid-solid multiphase flow model was established based on the Euler's multiphase flow model,and the internal flow field characteristics of the gas-liquid-solid multiphase liquid film in clearance seal were studied.Studies have shown that the presence of solid particles will increase the opening force of the liquid film to varying degrees,but under moderate speed conditions,the solid particles have a greater influence on the membrane pressure;The existence of solid particles will weaken the pumping effect to some extent,the outer wall of the spiral groove has a certain obstruction effect on the solid particles,and there is a possibility of particle accumulation in the groove area.2.The effects of gas-solid phase physical parameters such as solid particle diameter,particle inlet volume fraction,and gas nucleus content on the cavitation and lubrication performance of the liquid film were investigated.The results show that the inhibition ofcavitation decreases with the increase of particle diameter and gas nucleus content.The increase of the particle volume fraction has a stronger inhibitory effect on cavitation.The opening force of the liquid film generally increases first and then decreases with the particle diameter,and the particle size corresponding to the maximum opening force decreases with the increase of the rotation speed,increases with the increase of the particle volume fraction,and decreases with the increase of the gas nucleus content.The friction torque decreases slightly with increasing particle volume fraction and gas nucleus content.3.The influence of groove parameters such as groove depth,helix angle,groove diameter ratio and groove width ratio on the gas-liquid-solid multiphase flow characteristics,opening force and leakage amount were studied.Studies have shown that solid particles from the inner diameter side of the spiral groove mainly gather in the groove area and the inside of the dam area of the sealing surface;The size of liquid film cavitation decreases with the increase of groove depth,and increases with the increase of rotation speed,helix angle,and groove width ratio;generally choose 6-10?m groove depth,0.8 groove ratio,0.3-0.6 groove width ratio can obtain a larger liquid film opening force;Leakage at speeds higher than 1000 rpm is negative and the absolute value of leakage increases overall with as the speed and groove ratio increase,with the increase of groove depth and groove width ratio,it increases first and then decreases,and decreases with the increase of helix angle.4.On the basis of the above research on the gas-liquid-solid multiphase flow characteristics and sealing performance of microgap seal,the end surface morphology of different combined groove seal based on single spiral groove is proposed to explore the problem of reducing the clogging of dynamic pressure groove.The research shows that the combination of circular groove and spiral groove can effectively reduce the high volume fraction particles in the outer wall of spiral groove,and to some extent increase the opening force of liquid film and reduce the friction torque.It has certain effect in reducing the possibility of blockage of pump slot and improving the lubricating performance of seal.