A NUMERICAL STUDY OF THE PERFORMANCE OF A TURBOMOLECULAR PUMP

In the free molecular flow range, the pumping performance of a turbomo lecular pump has been predicted for various values of the dimensionles s blade velocity ratio C by employing the integral method and the test particle Monte-Carlo (MC) method in the calculation of the transmissi on probability. Also, new approximate method combining the double row solutions, so called double-approximation (DA), is presented here. The calculated values of transmission probability for the single row agre e quantitatively with the previous known numerical results. For a six- row pump, the MC method is employed to calculate the overall transmiss ion probability for the entire set of blade rows. When the results of the approximate method combining the single row solutions are compared with those of the MC method at C=0.4, the previously known approximat e method overestimates as much as 34% than does the MC method. But, th e new DA method gives more accurate results within 10% of relative err or with respect to the MC method.