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Simulation of Backflow Characteristics for Screw Vacuum Pump
Pages: 1295-1299
Year: Issue:  11
Journal: Chinese Journal of Vacuum Science and Technology

Keyword:  Screw vacuum pumpBackflow modelClearanceRotor parameterOptimization design;
Abstract: The backflow,from the high-pressured outlet to the low-pressured inlet through the narrow gaps between the rotors and side-wall of the single thread,fixed pitch screw vacuum pump,was empirically approximated,mathematically modeled as Poiseuille and Couette flows in the circumferential and radial gaps and holes flow in the flank gap,respectively,and numerically simulated in finite element method with self-developed program.The impact of the gap geometries,including but not limited to the radius of the involute base circle,outer and inner screw radiuses R and r,base circle radius r0,screw pitch T and tolerance,on the backflow behavior was investigated.The simulated results show that at a theoretical fixed pumping speed,the backflow significantly depends on the r/R ratio.To be specific,a decreased clearance strongly weakens the backflow.We suggest that at a given pumping speed,the backflow rate may be minimized at an r/R ratio of 0.65.
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