Theoretical Model for Predicting Steam-Ejector Performance

A simple theoretical model has been developed as an aid to designing steam ejectors. The ejector flow is modeled as comprising a number of continuum components such as potential flows and shear flows. Velocity profiles are approximated by stepped profiles, each flow component having a uniform velocity. Compressibility effects are accounted for by assuming isothermal flow in the mixing section. The differential equations governing momentum and mass transfers are integrated numerically, yielding pressure distribution predictions in the ejector mixing section, as a function of primary- and secondary-steam inlet states, and of mixing-section shape, in good agreement with published steam-ejector data. The model exhibits compound choking and compound supersonic flow in agreement with the data. While the isothermal-flow model has been tested only with steam-ejector data, it should be applicable for designing any ejector wherein the primary stream is a two-phase liquid-vapor mixture with the liquid fraction in small droplets occupying a negligible volume fraction. The model has been implemented via a FORTRAN computer program.