螺杆真空泵返流特性的研究

Simulation of Backflow Characteristics for Screw Vacuum Pump

以单头等螺距内凹转子双螺杆真空泵为研究对象,对螺杆真空泵工作时转子与泵腔、转子与转子之间气体的流动状态进行研究,将周向返流简化为两平面平板之间库埃特流动与泊肃叶流动,径向和齿侧返流简化为薄壁孔流动,建立了螺杆真空泵转子周向、径向和齿侧返流量计算的理论数学模型。计算分析了不同间隙值以及螺杆转子参数对螺杆真空泵返流量的影响,得到螺杆真空泵返流量随着螺杆渐开线基圆半径、大径、小径、和导程变化的规律。研究结果表明:周向间隙的增加使得返流量显著增加;在理论抽速给定的条件下,小径大径比为0.63时,返流量最小。

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, mathematical- ly modeled as Poiseuille and Couette flows in the circumferential and radial gaps and holes flow in the flank gap,respec- tively, 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 ra- dius r0,screw pitch T and tolerance,on the backflow behavior was investigated. The simulated results show that at a theo- retical 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.