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Three-Dimensional Flow Analysis of Radial Siegbahn Molecular Drag Vacuum Pump
H.-P. Cheng, J.-Y. Jang, C.-K Chyou

The CFD methodology is successfully applied to investigate the flow field of radial Siegbahn molecular drag vacuum pump in the continuum flow regime of low pressure. The rotors on both the upper and lower channels are equipped with a number of helical grooves that are separated by the thin blades. Six different groove number (6, 9, 12, 15, 18 and 20) and two different groove depths (3 and 5 mm) are examined. The non-orthogonal, body-fitted grid system is used to fit the curved pattern of the rotor blades. To simplify the computational model and shorten the calculation time, only one single flow channel including one groove of upper plane and one groove of lower plane is calculated. The full computational domain is linked in five sub-regions. The numerical results indicate that as the groove number is increased, the compression ratio of the pump is increased; as the groove depth is increased, the compression ratio is decreased. In addition, for 5-mm groove depth, although the average pressure is increased along the downstream in the upper groove, while it is decreased in the lower channel; this may harm the pump compression performance.

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