Simulation Of Characteristics Of Gas Flow In The Vacuum Leak In Monte Carlo

For the vacuum system,the contradiction exist between leakage and pumping to a certain extent,and this contradiction determines the ultimate gas tightness of the vacuum system and can reach the limit of the vacuum system,leak will certainly exist,but also a very important evaluation index of the vacuum system.Rarefied gas tends to exhibit complex flow characteristics in irregular geometric spaces,and traditional analytical methods can not meet the needs of problem solving.With the development of computer technology,Monte Carlo method(MC)has become an important method to study rarefied gas flow,which also provides a new method to study on the transmission characteristics of the vacuum leak.In this paper,Test Particle Monte Carlo(TPMC)method and Direct Simulation Monte Carlo method(DSMC)are used.Some practical examples(the vacuum system leak is simplified as a circular section of straight circular pipes or special shaped pipes and calculate transmission probabilities and conductances),their applications in the study of molecular flow and transition flow related to vacuum technology are discussed,draw some pressure nephograms inside the leaks.To further improve the system of theoretical research of vacuum leak,the theoretical calculation method can more effectively guide and application.In the theoretical analysis,the main aspects of the following work are done:(1)Transmission characteristics of straight pipes with curved cross section and special shaped composite pipe under the condition of molecular flow.Simulation of transmission characteristics under various simplified molecular flow pipeline leak,including transmission probabilities,conductances.All of these parameters decrease with the increase of the ratio of length to diameter pipeline leak,in the third chapter,on the basis of the ratio of length to diameter leaks on L/D=10 leaks changed in various shapes and other parameters using the method of TPMC to simulate in order to highly complex simulation of vacuum leaks,draw more accurate conclusions.(2)Transmission characteristics of a single gas in a straight circular pipea under transient flow regime.The leaks are simplified as two-dimensional model are arranged as straight circular pipe models with both ends of the "buffer zone ",the" buffer zone "represent the vacuum and atmospheric environment,using the DSMC method to obtain the transmission probabilities,and conductances,be provided the same change tendency with molecular flow,compared with the length changes of the leaks,Knudsen numbers are more obviously affecting the changes in these parameters,especially in larger Knudsen number and the pressure nephograms of pipes and streamlines,for detailed analysis of transmission characteristics of leaks.(3)The transmission characteristics of mixed gas in a straight circular pipes under transient flow regime.The N2,O2 and He can be divided into three gases according to the ratio of 78%,21%and 1%to simulate the composition of the compositions of air.DSMC method is used to obtain the transmission probabilities,and conductances,simulations on molecular flow and transition flow have a similar results.this is the longer the length,the transmission probability and the conductance value is smaller.the ratio of gas through the smaller,and the pressure nephograms of pipes and streamlines,for detailed analysis of transmission characteristics of leaks.