AVS 50th International Symposium
    Vacuum Technology Wednesday Sessions
       Session VT-WeP

Paper VT-WeP2
Thermodynamic Effects on the Pumping Performance of a Dry Scroll Vacuum Pump

Wednesday, November 5, 2003, 11:00 am, Room Hall A-C

Session: Poster Session
Presenter: T. Sawada, Akita University, Japan
Authors: T. Sawada, Akita University, Japan
S. Kamada, Akita University, Japan
W. Sugiyama, Akita University, Japan
M. Yabuki, Akita University, Japan
M. Fujioka, ANEST IWATA Corporation, Japan
M. Tsuchiya, ANEST IWATA Corporation, Japan
Correspondent: Click to Email
The theory we proposed before gives the ultimate pressures closely consistent with the values from the actual machine at the rated speed, but gives smaller values than the actual machine does, for lower orbiting speed. This discrepancy increases as the orbiting speed decreases. The theory also seems to be incomplete for other gases than nitrogen, especially for a light gas like helium. It has been confirmed experimentally that this is caused by the difference in clearance between the theoretical analysis and the actual machine. The clearance is constant in the theoretical analysis regardless of the orbiting speed and the type of gases; however, the clearance in the actual machine changes with the temperature changes accompanying variations in orbiting speed and the differences in the thermophysical properties of gases. We propose a thermodynamic model expressing the temperature distributions on the orbiting and fixed scrolls. Since the heat generated in a suction side pockets is very small, it is considered that the heat generated by gas compression is carried adiabatically to around the shaft and then conducted to the orbiting scroll and the fixed scrolls. The temperature of the orbiting scroll rises higher than that of the fixed scrolls because the fixed scrolls are cooled more easily than the orbiting scroll. Then, we obtain the clearance change under the obtained temperature distribution and predict the ultimate pressure of the pump having the changed clearance. The predicted ultimate pressure agrees pretty well with the measured one throughout the experimented range of orbiting speed for all tested gases (nitrogen, argon and helium).