The Effects Of Structure Parameters On The Vapor Jet Flow Field Of Oil Diffusion Pump

Compared with other types of vacuum pumps, the structure of oil diffusion pump is more simple. It has no moving parts, vibration and noise and is easy to use. It has a longer life than other types of pumps and lower cost. So it is widely used in scientific research of various fields, such as electronics, metallurgy, chemical, nuclear and other industrial sectors and space technology. However, the working material of diffusion pump is diffusion pump oil. Despite a number of measures has been taken, oil pollution problem caused by the oil of diffusion pump refluxing to the high vacuum side has always been the main reason for restricting diffusion pump applications.Improving the evacuating performance and exhausting steadiness and reducing the rate of reflux in oil diffusion pump is the main problem to be solved. The low refluxing rate of diffusion pump oil is the most important porblem in the current research of sentific center and manufanturing company. The refluxing rate of diffusion pump oil is affected by inlet pressure, the shape and size of first stage nozzle, the gap of multi-level series nozzle, the type of oil, the location of oil diffusion pump caps and slinger and other factors. These factors determine the diffusion pump oil vapors jet state and flow structures. Due to the classical theory of diffusion pump is difficult to describe and quantify accurately reflect the diffusion pump oil vapor jet flow characteristics, on the basis of analysising pumping mechanism of diffusion pump, the internal steam jet field of K800 diffusion pump was simulated by computational fluid dynamics software Ansys-workbench. It turns out the diffusion pump flow field and exhausting characteristics are affected by the first stage nozzle structure, slinger position, the oil cap size and the gap of grade tandem nozzle. The results has certain guiding significance for understanding the mechanism of diffusion pump suction, improving the pumping performance of diffusion pump, reducing the refluxing rate of diffusion pump oil.Simulation results show that the exit velocity of nozzle is affected by throat size, the velocity increases with the decreasing of pump throat gap and the enlargement of nozzle opening angle. The oil cap is too long or too short is not conducive to the suction effect of diffusion pump and there is the best oil cap structure size matching with the vapor jet field. The location of diffusion pump slinger impacts vapor jet flow field and vortex formation, decides the refluxing rate of diffusion pump oil and seting the slinger position correctly play a crucial role on reducing the refluxing rate of diffusion pump oil. The distance of series two-stage nozzle is greater, the effect of oil vapor condensation is better, but pumping efficiency is reduced. If the distance is too small, it will affect the normal operation of diffusion pump. Designing a reasonable distance of series two-stage nozzle need to take into account the stability of pumping and the compactedness of the structure.