Some of the Parameters Affecting Knudsen Effusion. IV. Monte Carlo Calculations of Effusion Probabilities and Flux Gradients for Knudsen Cells

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Abstract
Data are presented for effusion probabilities and cell-wall flux gradients calculated dynamically by means of Monte Carlo computer studies. Typical effusion cell dimensions were programmed for both knife-edged and Clausing orifices; all calculations apply to a flat sample. The influence of the size and the length-to-radius ratio of the orifice and the effects of different condensation coefficients are described. An analytical expression relating the equilibrium sample flux to the flux at steady state has been derived. It is shown that for a given cell design, the ratio of these fluxes is constant and independent of the nature of the vaporizing species. Because the Monte Carlo method requires no mathematical approximations or simplifying assumptions, results analogous to real cell behavior are to be expected. Comparison of these results with the treatment derived by Motzfeldt shows that his formula is applicable and quite accurate over a wide range of experimentally encountered conditions.