A nonequilibrium model is developed to describe the two-phase critical discharge of initially saturated and subcooled liquid through sharp edged inlet, constant area ducts with L/D ≥ 12. A similar model is proposed for smooth inlet geometries with L/D ≥ 0. The proposed solutions, which are based on the upstream stagnation conditions, exhibit excellent agreement with the published data which include water, Freon-11, and Freon-12 results.