General geometry calculations of one-stage molecular flow transmission probabilities for turbomolecular pumps

Abstract

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.

Design and analysis of vacuum air-intake device used in air-breathing electric propulsion

“…5. The total number of the simulated particles is at least 2×10 6 for each value to ensure that the relative statistic error is less than 0.1% [26]. Tables 1 and 2, with the increase of the altitude, the atmospheric temperature T s will increase and the average particle mass M a1 will reduce, these will lead to the increase of the thermal motion velocity of the incident particles, and worsen the directivity of the incident molecular flow.…”

“…The 3D test-particle Monte Carlo (TPMC) methods of the turbo in the molecular flow regime are reported in Refs. [23][24][25][26][27]. The intermolecular collisions are ignored in TPMC simulation, and the calculation time will be reduced significantly compared with that of DSMC simulation.…”

The Pumping Performance of a Multiport Hybrid Molecular Pump and Its Effect on the Inspection Performance of a Helium Mass Spectrometer Leak Detector

“…Finally, the ratio of the number of molecules that pass the blade to the total number of molecules, which is the transmission probability, is obtained [20,21]. The relationship between the transmission probability and turbine blade parameters can be obtained by changing the blade inclination, pitch chord ratio and speed ratio [22,23].…”

Monte Carlo simulation of gas free molecular flow in turbo molecular pump’s inlet tube

“…A number of investigations have been carried out on the pumping principle [1], key structures [2][3][4][5][6] and manufacturing technologies [7] of the pump. Among the studies on effective pumping speed of TMP, especially the pumping mechanism, at the turbine blades region, either with the 2D model [8][9][10] or 3D model [11][12][13][14][15], most of them are based on the hypothesis that the incident gas molecules (IGM) distribute uniformly at the turbine blades surface [8][9][10][11][12][13][14][15]. Between circular inlet surface of the tube and the annular surface of turbine blades, the flow resistance of the inlet tube is usually disregarded or simply regarded as that of a short tube.…”