Hydrodynamic modeling of the rapid expansion of a supercritical solution through an orifice was proposed. The expansion process was subdivided into three successive steps - at the nozzle inlet, along the nozzle itself, and in the expansion chamber. Three thermodynamic transformations were considered, one for each step of the expansion process. Temperature and pressure profiles were calculated. Flow rates at the exit of the nozzle and temperature profiles were measured downstream the nozzle exit for two supercritical solvents, CO2 and CHF3, and for different preexpansion temperatures and pressures. Computed values compared fairly well with the experimental data.