Net molecular flow conductance of series elements

The problem of calculating the total molecular flow conductance of ductwork made up of series connections of elements of known conductance is discussed from the transmission probability point of view. Cases in which there is a discontinuity in cross section between adjacent elements are included. Two criteria for evaluating methods for this calculation are discussed and applied to two such methods. One method, which includes a short procedure for treating discontinuities in duct cross section, is shown to satisfy both evaluation criteria