Study On The Deposition Characteristics Of Solid Particles In Lubricating Film And Seal Performance Of Liquid Mechanical Seal

In the actual operation of liquid dynamic pressure mechanical seals,tiny solid particles often enter the lubricating film in sealing gap due to the sealing medium or the negative pressure of the dynamic pressure groove on the end surface,causing the flow field characteristics of the lubricating film to change and the dynamic pressure groove being blocked due to deposition which will lead to seal failure in severe cases.To this end,with the support of the National Natural Science Foundation of China(51976078),this paper takes the liquid dynamic pressure mechanical seal as the research object and establishes a gas-liquid-solid multiphase flow calculation model involving micro solid particles and cavitation of liquid film.The influence of particle physical parameters,working condition parameters,face groove parameters and medium temperature on the movement and deposition characteristics of solid particles in micro-gap lubricating film and sealing performance were studied.It will provide a theoretical reference for the research and development of high-performance liquid face seals.The main works and conclusions are as follows:1.Using the upstream pumping mechanical seal as the specific research object,a multiphase flow calculation model for the sealing micro-gap lubricating film was established based on the Laminar model,Mixture multiphase flow model,Zwart-Gerber-Belamri cavitation model and DPM model in Fluent.The model was verified.The multiphase flow characteristics of the lubricating film and the movement and deposition of solid particles were studied.The research shows that there is a high-pressure zone in the outer groove root of the spiral groove and a low-pressure zone is formed from the leeward side to the inner groove root.Cavitation occurs in the middle of the weir zone on the leeward side.When the rotation speed increases,both the high-pressure area and the low-pressure area(including cavitation area)increase,and the medium-pressure area decreases when the medium pressure increases.After the solid particles are sucked in the low-pressure area of the trough weir,they are mainly deposited on the upstream boundary and leeward side of the low-pressure area in the trough,as well as on the cavitation upstream boundary and the outer groove root circumference.2.The effects of parameters such as solid particle diameter,particle inlet volume fraction,speed,medium pressure and lubricating film thickness on the distribution,deposition rate ofsolid particles and sealing lubricating performance of the sealing micro-gap lubricating film were studied.The research shows that the low pressure area of the spiral groove is the main part of solid particle deposition.The increase in size of the particle and volume fraction of the particle inlet expands to the outer groove root and the dam area.Increased speed and medium pressure cause the deposition area to move towards the inner diameter side.At low speeds,deposition are likely to appear in the dam area and the deposition in the non-groove area are distributed circumferentially.Smaller particle size,increased rotation speed,increased medium pressure,and reduced film thickness are beneficial to reduce the particle deposition rate.Moderate particle size,particle inlet volume fraction increases at low speed,inlet volume fraction decreases at high speed,speed and medium pressure increase,and film thickness decreases to improve the opening force of the lubricating film.The friction torque increases with the increase of particle size,rotation speed,medium pressure and particle inlet volume fraction,and decreases with the increase of film thickness.The leakage volume shifts to the positive leakage direction with the increase of particle size,particle inlet volume fraction and medium pressure,and to the negative leakage direction with the increase of speed and film thickness.3.The influence of groove shape parameters such as groove depth,helix angle,groove diameter ratio and groove width ratio on the deposition distribution of solid particles,deposition rate and sealing lubricating performance of the lubricating film were studied.Studies have shown that small groove depths are prone to circumferential grain deposits in the dam area.Too small or too large helix angles,too large groove width ratios,and too small or too large groove diameter ratios at low speeds will lead to increased deposition of particles in the groove area.When the groove depth is about 6?m and the helix angle is about 18°,the particle deposition rate is the smallest.At low speeds,the deposition rate is sensitive to the groove diameter ratio and increases significantly as the groove diameter ratio increases.When the rotation speed is increased to more than 2000 rpm and the groove diameter ratio is about 0.5,the deposition rate is the largest.The increase of the groove width ratio leads to the increase of the deposition rate.Sudden increase in deposition rate at high speeds and high groove width ratios.The maximum opening force can be obtained when the groove depth is about 6~10?m(high speed takes a large value),the groove width ratio is about 0.2~0.5(high speed takes a small value),and the groove diameter ratio is about 0.8.The increase of the helix angle leads to the decrease of the openingforce.The friction torque decreases with the increase of the groove diameter ratio and the groove width ratio,but is little affected by the change of the groove depth and the helix angle.When the rotation speed is higher,a smaller groove depth and a larger groove width ratio can obtain a smaller negative leakage amount.The negative leakage amount increases with the increase of the groove diameter ratio and decreases with the increase of the helix angle.4.The effect of medium temperature on the motion and deposition characteristics of solid particles and the dynamic pressure lubrication of the seal were studied.Studies have shown that with the temperature of the medium increases,the maximum membrane pressure and the high-pressure area decrease,the low-temperature area shrinks slightly,and the high-temperature area temperature increases significantly.The particles are more likely to enter the lubricating film in the groove and weir area,and also easier to escape from the inner diameter side to reduce the deposited particles.It leads to reduced particle deposition rate,reduced opening force,reduced friction torque,and increased leakage.When the medium pressure rises,the high temperature area expands.When the speed increases,the low temperature area increases and the temperature in the dam area rises.