Masashi Iguchi

Pumping Performance Analysis of Turbine Blade with a Narrow Inter-stage Clearance

The performance of turbine blades under a medium vacuum was investigated using the Stokes equation in a previous paper, where we could predict the performance of the turbo molecular pump in the pressure range of under 10 Pa. For further improvement of the pumping performance of turbine blades under a medium vacuum, experiments were carried out with a pump which has a narrow clearance between the rotor and the stator blade compared with the conventional pump. As a result, we found that the narrow clearance pump had a high performance under a medium vacuum compared with the conventional pump. Therefore, we analyzed the flow field in the turbo molecular pump by the two dimensional Finite Element Method (FEM). In order to examine the influence of the interstage clearance, the model was changed from the single stage of turbine blade to the combination of stator blade rotor blade stator blade. The comparison between the measurements and the predicted values shows a good agreement under 10 Pa.

An approach to improve initial pump-down speed of turbomolecular pumps by water-repellent coating on the blades

Abstract Outgassing from turbomolecular pump (TMP) blades affects not only the ultimate pressure but also the initial rate of decrease of the inlet pressure. A longer evacuation time to attain a high vacuum is required for TMP than for a cryopump, because TMPs pumping speed for water, the dominant species of desorbed gases, is lower than that of the cryopump. The aim of this study is to develop a TMP which enables quick evacuation without the use of a cryotrap. The surface free energy or the water-repellent characteristics are considered to be important in the evacuation of water from surfaces. A special surface coating which has better water-repellent characteristics than an uncoated surface of aluminum alloy was developed, and outgassing from this surface was investigated.