| Oil diffusion pump is one of the main devices to obtain high and ultrahigh vacuum environment which is widely applied in machinery,metallurgy,aerospace and other scientific fields.Oil diffusion pump has many advantages,such as large pumping speed,high vacuum degree availability,simple structure,convenient operation,no mechanical transmission,no vibration and noise and long service life.Gradually,it is recognized and accepted by plenty of users at home and abroad.However,the reflux of pump is an inevitable inherent shortcoming,which severely limited its expanding sue.Therefore,it has been an great effect for researchers and users of oil diffusion pump to improve the working performance,optimize the pump structure and reduce the backflow of diffusion pump for several years.The state of flow field and shape of steam jet in oil diffusion pump directly determines the merits of its working performance(pumping rate,oil return rate,etc).So this paper studies the rule of inner flow field and jet configuration of steam jet inside the oil diffusion pump by computational fluid dynamics(CFD)and tries to provide some reference value to later researchers for deepening the understanding of the pumping mechanism,improving the performance and reducing reflux rate of oil diffusion pump.Based on the above background,Fluent software is used to simulate the flow field and reflux phenomenon of oil diffusion pump in this article.The main contents are as follows:(1)The effects of the geometrical parameters and the structure on the flow field and steam jet of the k-400 single stage oil diffusion pump were studied.The differences of the flow field under different nozzle angles,different throat gaps and different structures were compared.Research results shows that the optimal value with the best performance of the pump is a 55° nozzle angle,a 2.5mm clearance and an tapered—throat—divergent nozzle structure.(2)Taking the reflux phenomenon of pump into account,three different structures of oil retaining cap and the optimum of skirts length were compared.Simulation result shows that a structure which has the same shape with the oil retaining cap and the nozzle extends vertically downwards is the best choice,the skirts length with-10mm of lower edge is a appropriate value(the base of the nozzle is zero datum).(3)The anti-backflow effect of cold trap baffle was studied and the numerical simulations were carried out under different installation quantities,angles and structures respectively.Numerical study results show that when the number of baffles is three,the chevron structure with 55° assembly is the best choice.(4)For convex cavity oil diffusion pump of K-400T,the flow field in the pump under two different structures and different cavity areas were studied respectively.Numerical simulation result shows that when the ratio of the diameter of the convex cavity to the diameter of the pump port is 1.1,the structure of the circular convex cavity pump is the optimal choice,the simulation result of flow field in pump after broaden pump body according to the convex cavity diameter also verify this conclusion. |
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