Research On Vaporization Characteristics Of Fluid Film And Performance In Hydrodynamic Mechanical Seals

Fluid film vaporization is an unavoidable problem in the research and application of hydrodynamic lubrication mechanical seals,and has even become one of the obstacles to its application to higher operation conditions.When fluid film vaporization occurs,it not only affects the performance of the mechanical seals,but affects the stability of the seals or even causes premature seal failure.The research on mechanical seals fluid film vaporization is far from mature and perfect in theoretical research and engineering application.Therefore,in this paper,the theoretical analysis and model of fluid film vaporization for hydrodynamic lubrication mechanical seals are carried out,and the fluid film vaporization characteristics and its influence on the seal performance are studied,in order to provide theoretical reference for improving stability and performance of seals or avoiding seal failure caused by vaporization.The main research contents and conclusions of this paper are as follows:1.This paper takes the upstream pumping hydrodynamic lubrication mechanical seals as the specific research object.On the basis of considering the relationship between water saturation temperature and pressure,viscosity-temperature effect and Newtonian fluid inner friction effect,the fluid film vaporization calculation model for hydrodynamic mechanical seals is established,and its validity is verified.2.Based on the fluid film vaporization calculation model for hydrodynamic mechanical seals,considering the relationship between saturation temperature and pressure,the influence of the viscosity-temperature effect and Newtonian fluid inner friction effect on the fluid film vaporization characteristics of the mechanical seals were studied.The results show that the effect of viscosity-temperature effect and Newtonian fluid inner friction effect on mechanical seals performance mainly depends on the medium viscosity.While considering the relationship between saturation temperature and pressure,ignoring the viscosity-temperature effect will have a great influence on the fluid film vaporization characteristics of the mechanical seals.Especially at higher rotational speed,the calculation results will obviously deviate from the theoretical reality.3.The effect of operation conditions and film thickness on the fluid film vaporization characteristics and performance of mechanical seals was studied.The results show that theaverage vapor volume fraction in the fluid film increases with the increase of the medium temperature.Its change rate begins to be gentle.Then,at a certain temperature value,the mutation will start to increase sharply,and the temperature value of mutation will increases with increasing rotational speed.When the film thickness is 3?m and 4?m,the average vapor volume fraction decreases rapidly with the increase of rotational speed,then abruptly changes at a certain rotational speed and begins to increase slowly;When the film thickness is 2?m,it always decreases with the increase of the rotational speed.The average vapor volume fraction decreases as the medium pressure increases,and the higher the medium temperature,the faster the decrease rate.The mutation of the open force,leakage and friction torque occurs at the same position where the average vapor volume fraction is abrupt,which indicates that the phase change of the fluid film has a significant influence on the performance of mechanical seals.When the medium pressure is constant,the core region of fluid film phase change is different under the different matching of rotational speed and medium temperature;when both the medium temperature and the rotational speed are high,the core region of phase change will move to the upstream side and the windward side.4.Transient calculation of the mechanical seals fluid film vaporization was carried out,and the influence of the fluid film vaporization on the seal failure was briefly analyzed.The results show that After the mechanical seals started running,the average vapor volume fraction in the fluid film increases rapidly within a few milliseconds.The trend of open force,leakage and friction torque,etc.is closely related to the average vapor volume fraction.When fluid film vaporization occurs,the growth and collapse of bubbles and the thermal stress due to alternating high and low temperature may cause damage to the seal ring materials,resulting in damage and failure to the seal rings.Both external and internal factors can make the fluid film of mechanical seals unstable and cause the seal failure,but the essence is due to the instability of the two-phase hybrid lubrication.