Effusion. IV. Angular Number Distributions of Gaseous CsCl from Right-Circular Cylindrical Orifices into Vacuum

Abstract

Angular number distributions of CsCl(g) effusing from right-circular cylindrical orifices located in the walls of double-oven effusion cells with L / d (ratio of orifice length to diameter) of 0.467 and 1.29 were measured by means of a surface ionization detector. The distributions have been studied as a function of the state of the gas in the effusion cell. A high-pressure limit for molecular flow was found to be approximately at a K (ratio of mean-free path to diameter) value of 1.9 for the longer orifice; the limit for the short orifice was not observed. For the long orifice, as K decreased below 1.9, the probability of effusion in the forward direction decreased. At K larger than 1.9, the angular number distributions were not in agreement with the Clausing theory and fluctuations in the distributions were noted. The results found in this work are compared with those of previous investigators. The effects at K > 1.9 may be explained by introducing specular reflection of molecules from the orifice walls.