In this study, a 1D analysis has been presented for the prediction of ejector performance at critical mode operation. The new triple-choking model has been developed using the governing equations of the compressible fluids and thermodynamics properties based on the frictional adiabatic fluid study. A new approach has been introduced to consider the frictional effects on the mixing efficiencies by extending the 1D ejector theory. A very good agreement has been reported for the R141b and steam experimental data at critical mode operation. Furthermore, simulated results have been compared with some of the recent theoretical models. In addition, the influence of operation conditions on the ejector performance and the required cross-sectional area of the mixing chamber has been showed. Finally, the influence of the operation conditions (such as generator, condenser, and evaporator temperatures) and the size of ejector on the mixing efficiency have been studied.