SIMULATION OF RAREFIED VAPOR FLOWS

The vapor region between evaporator and condenser surfaces of different areas is examined by direct Monte Carlo simulation of multicomponent, high-vacuum distillation. Vapor profiles change sharply through the kinetic layer next to the evaporator and again through that next to the condenser. The center region, usually the longest part, shows relatively gentle changes, owing mainly to the expansion toward the greater area of the condenser. This is the region of uniform flow, with point properties close to the equilibrium values, that has often been postulated for high-vacuum flows. Simulated rates agree satisfactorily with experimental data for binary systems if the intermolecular potential is sufficiently realistic. Thus, a hard-sphere model yields excessive deflection and low estimates of rate, while an inverse, power-law model gives improved agreement. Selectivities of separation are generally in excellent agreement with values calculated by other means and with experiment, provided, in the latter case, that nonideal behavior in the liquid solutions is adequately modeled.