Study On The Pumping Performances Of Vortex Structures Under Continuous Flow

High vacuum dry pump working directly against atmosphere has become one ofresearch hotspots in the field of vacuum production due to its compact structure andoil-free high vacuum. Being small in size, simple in structure, and easy to makemultistage design, vortex structure is often used in exhaust side of the pump, and itspumping performance significantly determines that of the high vacuum dry pump.In this paper, computational fluid dynamics(CFD) method was used to study theinfluence of vortex structures on the pumping performance of the pump undercontinuous gas flow. The results of the research shows:1）Gas follows a helical path through the toroidal channel in which a clearlylongitudinal vortex is occured. This is in high accord with experimental results. Theresults suggest that the internal flow in the vortex structure under continuous flow canbe exactly simulated by means of sliding grids in CFX software，while the simulation isnot accurate if immersed solids capability of CFX software is used, since nolongitudinal vortex is observed in the flow channel in this case.2）Compression ratio of the pump increases with the rise of its rotating speed,decreases with the rise of temperature, inlet mass flow and outlet pressure. A betterpumping performance can be achieved by increasing the rotating speed and pumpingcold air. Multistage vortex structures in series can achieve high ultimate vacuum andbring the gas in the channel into transitional flow state.3）Compression ratio increases with the decrease of the clearance. Under thecondition of different rotating speed and outlet pressure, the calculation shows thatvortex structure within48-72blades has better pumping performance, the optimalnumber of blades is about60in each condition, and the performance of circular channelstructure is better than that of rectangular channel structure.4）The comparison of different single-stage vortex structure shows that the pumpingperformance of EPX pump is superior to that of Ontool pump. The total compressionratio of multistage vortex structure depend not only on the ratio of each stage, but alsoon the reflux condition in the clearance between different stages. The reasonableclearances can greatly reduce the reflux and thus, get better pumping performance.