TRANSMISSION PROBABILITIES OF GAS MOLECULES THROUGH FINITE-LENGTH TUBES IN TRANSITION RANGES

Dilute gas flows through finite length circular tubes were numerically simulated by the Direct Simulation of Monte Carlo method. The Direct Simulation of Monte Carlo method can simulate both the collisions of molecule-molecule and molecule-solid surfaces. The simulated transmission probabilities of mono-atomic gas molecules through the tubes were compared with the free molecular flow theory in order to evaluate the numerical accuracy of the method. The numerical probabilities in the free molecular range coincide with the theory (to an accuracy of +/- 2%). In the flow range from transition flows to slip flows, the ratios of the conductances through the finite length tubes to the conductances through a zero - length circular slit at the free molecular flow are in accord with the experimental equation (to an accuracy of +/- 5%).