Effect of side streams on supersonic gas separations

Supersonic gas separators are converging-diverging nozzles with side streams that remove condensed phases. Computational fluid dynamics is often used for the analysis and mechanical design of such units because of the detailed data it provides, thanks to the many grid points that sample fluid behavior within the equipment. Less common is the use of models with simpler geometric assumptions but rigorous evaluations of the thermodynamic properties of the flowing fluid. Such models are useful for preliminary design if they capture the essential features of the phenomena that occur within the nozzle. This article presents a one-dimensional flow model for supersonic nozzles with side streams under continuous, steady-state operation. The procedure involves several steps, which require solving of isentropic and isenthalpic flash problems and predicting the thermodynamic sound speed. These calculations use rigorous algorithms and thermodynamic properties evaluated with the Peng-Robinson equation of state. Nonetheless, the procedure is general and allows the use of other equations of state. The results are in good agreement with experimental data from the literature. In addition, a parametric sensitivity study shows that the model predicts meaningful trends. The set of results indicates that the model is potentially useful for the conceptual design of supersonic separators.