Conductance of Tubes and Ducts

Generally, the conductance of a tube or a duct can be regarded as the conductance of the tube/orifice opening (Cap) multiplied by a probability factor representing the proportion of particles leaving the exit of the conductance  

1 Molecular Flow Conductance of an Orifice with Significant Wall Thickness (t). 

Let t be small compared to d. If px p2 (in the appropriate pressure range) the particle flux through the aperture (area A) from px to p2 will be  

however, the same particles collide with the walls of the aperture, then the number of particles arriving at the wall will be  

2 Molecular Flow through Tubes of Constant Cross-section. The conductance is determined by the rate at which particles enter the tube/ duct and the probability that these molecules will be transmitted through 

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