On the nonlinear pressure dependence of the flow rate in crossed-beam experiments

We show from simple conductance considerations in the intermediate flow regime, i.e. in the pressure regime adjoining molecular flow, that a nonlinear behaviour of the flow rate as a function of backing pressure behind a nozzle is to be expected. For Knudsen numbers a second-order polynomial fits the experimental observations well. The results have been applied to all available data in the literature.