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Articles you may be interested inEffect of inlet guide vanes and sharp blades on the performance of a turbomolecular pump Empirical formulae for the compression ratio and speed factor of a single stage turbomolecular pump operating in the molecular flow regime are developed for blade speeds lower than the most probable molecular velocity. These formulae are based on Becker's compression formula derived from drag theory and on Bernhardt's pumping speed formula but are modified and extended to take account of the full range of parameters in the two dimensional infinite blade row model of Kruger. Numerical constants are determined using the direct simulation Monte Carlo method. Results from the latter method are presented as contour plots of transmission probabilities intended to cover cases of interest for design calculations.

Compression ratio and leakage through stages in turbomolecular pumps J. Vac. Sci. Technol. A 9, 2058 (1991); 10.1116/1.577412 Calculation and measurement of the volume flow rate dependence of turbomolecular pumps on the type of gas J. Vac. Sci. Technol. A 7, 2365 (1989); 10.1116/1.575900 Onestage and twostage temporal patterns of velar coarticulationIn this paper the pumping mechanism of a single stage of a turbomolecular pump ͑TMP͒ is addressed. A collisionless gas, a Maxwellian distribution of particles at the inlet and outlet surfaces of the passage, and diffuse reflection for the particles that collide with the walls of the passage are assumed. Models of this type have, until now, only been applied to the two-dimensional ͑2D͒ case, i.e., the TMP stage was approximated by an infinite row of blades. This approximation can only be valid for very narrow passages, far from the axis of rotation. In the present work the 2D case has been assessed in detail as a basis for confidence in three-dimensional ͑3D͒ modeling. The main difficulties in modeling the 3D case arise from the geometric complexity and the rotating frame of reference. As a result of the latter, particle orbits are no longer straight lines, and their intersection with the walls has to be calculated iteratively. The Monte Carlo method was chosen to model the 3D case as it appears to have significant advantages. The passage is divided into layers normal to the axis of rotation, and a particle proceeds at every time step to the next or previous layer. This technique of tracking saves computer time as it takes advantage of certain characteristics of the rotational system. Results for different types of blade passages are presented.

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