Study On Gas Flow Characteristics And Sealing Performance Of Metal Sealing Gap Of Gate Valve

With the rapid development of global industrialization,the use of gate valves is gradually increasing.Under high temperature and high pressure,the sealing surface of gate valves is mostly in the form of metal seal.At present,the metal seal structure design of gate valve is mainly based on experiences.The lack of the leak calculation method restricts the design of gate valve with high sealing performance.In the process of design and production,many tests are often passed,resulting in high design cost and low production efficiency.The main reason is that the metal seal is manifested as two metal planes in contact with each other on the macro level,and the micro level is manifested as the mutual Mosaic between the micro convex bodies on the metal surface,and the un-contact area is connected to form a leak channel.However,the metal seal gap leak channel is not accurately constructed and the micro-flow characteristics of the gas medium in the rough surface micro-channel are not accurately described,which leads to the failure to calculate the metal seal leak rate accurately.To solve this problem,based on the annular morphology of the metal sealing surface,the contact calculation of the sealing process was carried out by using the anisotropic rough surface,the leak channel was extracted from the contact model,the gas flow characteristics in the rough surface microchannel were studied,and the leak rate calculation model was established.The validity and rationality of the model are verified by experiments,which provides a theoretical basis for the design of metal seal.The main research contents of this paper are as follows:(1)The sealing surface is reconstructed by the radial roughness Rax and circumferential roughness Ray,combined with the W-M function.It can be found that the micro-morphology of the sealing surface reconstructed by W-M function is consistent with that of the actual sealing surface.By comparing the contact area ratio,the number of empty masses and the height of the sealing clearance in the sealing state,it is found that the influence of roughness on the sealing state is mainly reflected in the height of the sealing clearance,that is,under the condition of a certain specific sealing pressure,the sealing clearance height of the sealing surface with high roughness is larger.(2)Considering the influence of thin gas effect and topography effect in rough surface channel on gas flow characteristics,it can be found that for smooth flat channel,when Kn number is constant,the gas velocity distribution in smooth flat channel is determined.The normalized velocity distribution curve along the channel height is parabolic shape,and the center of the channel is symmetric.With the increase of Kn number,the slip velocity at the wall increases significantly,and the overall velocity distribution increases.However,in the rough channel,the wall convex has a significant disturbance effect on the local gas flow,and the streamline adjacent to the wall is distorted into the shape of the wall curve.At the same time,the velocity distribution in the channel shows an asymmetry,and the pressure drop along the flow direction presents a linear fluctuation.With the increase of roughness,the influence of surface convex on the gas flow in the channel increases gradually.(3)On the basis of the construction of the metal seal leak channel model and the study of the gas flow characteristics in the leak channel,the leak rate calculation model is proposed,and the leak rate experiment platform is designed to verify the leak rate calculation model.By comparing the calculation and test,it can be found that the maximum deviation between the calculated leak rate and the test leak rate is only 16.36%.Under limited conditions,Considering the simplification of the leak rate calculation model and the error of the test,the accuracy and effectiveness of the leak rate calculation model are proved.By studying the sealing performance,it is found that under the same sealing structure and sealing conditions,the leak rate of sealing surface with high roughness is high.For the sealing surface determined by sealing structure,the leak rate increases gradually with the increase of medium pressure;With the increase of sealing load,the leak rate decreases gradually.For the sealing structure under certain working conditions,the leak rate increases first and then decreases with the increase of sealing surface width.To sum up,the roughness and width of sealing surface are the main factors affecting the leak rate in the design of sealing structure.Considering the strength of sealing surface material,the rough surface with larger width and smaller roughness should be selected in the design.This paper studies the change of the contact state and the gas flow characteristics in the leak channel during the metal sealing process,and establishes the calculation model of the leak rate,which has important social and economic value and practical significance for the metal sealing structure to reduce the design cost,shorten the design cycle and improve the production efficiency.