Effect of Rotor Clearance on Pressure Ratio and Pumping Speed of Molecular Pump
Nomenclature d/b = clearance ratio Lib — aspect ratio Nj = molecular number incident on the blade row per unit time from region / Pi = pressure in region / Pj = probability that molecules incident from low-density side of a blade with clearance will be transmitted through the blades Q = ratio of the net through flow in molecules per unit time per unit area to the incident flux upon the blade from upstream side Ql = probability that molecules incident from highdensity side of a blade with clearance will be transmitted through the blades sib = spacing/chord ratio S = ratio of the mean mass speed of the gas, relative to the blades, to the most probable molecular speed; speed ratio a. = blade angle with the tangential direction £ = transmission coefficient in the clearance area D/2 = transmission coefficient (the fraction of molecules incident on side 1 of the blade row, which ultimately emerge to side 2)