Conductance Calculation Of Slot Channels with Variable Cross Section

Abstract

The range of operation pressures of non‐contact vacuum pumps may reach six decades, and flow regime in slot channels of the rotor mechanism may vary from molecular flow to viscous flow. This article is a continuation of a series of authors‘ publications dedicated to the development of a method which makes it possible to calculate promptly the conductance of slot channels with complex contoured geometry with the minimal clearance at a certain point along gas flow direction for all three gas flow regimes: molecular, transient and viscous. The numerical solution of the differential equations system (equations of motion, energy, continuity and state) is used for calculation of mass flow rate in transient gas flow regime. On the basis of the numerical calculation results the relationship is obtained which represents a smooth joining of the data for molecular and viscous flow regimes. Verification of the model and the obtained relationship is carried out by comparison of numerical calculation results of gas mass flow rate and conductance with experimental data obtained by blowing‐through of slot channels. The maximal deviation of calculation according to the obtained relationship from the experiment does not exceed 14%, the average uncertainty being less than 8%, which makes it possible to recommend it for practical application in transient flow regime.

Efficiency improvement of Roots vacuum pump working process

“…At low pressures pump characteristics are mainly influenced by backward flow through channels in rotor mechanism. That is why articles [14,15] covering study of such channels conductance are of considerable interest. Profile effectiveness is considered from the viewpoint of channels conductance decrease in [15][16][17].…”

“…That is why articles [14,15] covering study of such channels conductance are of considerable interest. Profile effectiveness is considered from the viewpoint of channels conductance decrease in [15][16][17]. It was showed that minimum backward flow through inter-rotor channel is obtained for elliptical profile with b/a ≈ 0.84 ÷ 0.86 and r/a = 0.610 ÷ 0.64 in free molecular flow regime.…”

Non‐contact vacuum pumps

“…It is very important to calculate the conductance of the rotor mechanism slot channels exactly, because pumping characteristics of any non-contact pump depend on backward flow [7]. That is why a lot of papers concerning development of calculation methods are devoted to study of pumps slot channels conductance [8,9].…”