A new model is described for nonequilibrium vapor production (flashing) in critical two-phase flow. The model is based on a description of turbulence enhanced thermal diffusivity in the liquid and a Weber number criterion for bubble size. In a quiescent environment, the model reduces to the well-known conduction controlled rate. Results of calculations are compared with flow rate and pressure data from blowdown experiments with various nozzle geometries. The nozzle throat diameters range from 1.8 to 51.0 cm and nozzle inlet conditions vary from water subcooled 30°C to saturated water at 98% vapor volume fraction. The calculations are made with the two-fluid code K-FIX and show very good agreement throughout the entire blowdown.