Abstract
This paper describes the formulation of two-phase flow equation under phase equilibrium and flow dynamics in one-dimensional nozzle. The derivatives of average specific volume and enthalpy were derived by using thermodynamic relationships. By introducing Clapeyron-Clausius equation, these derivatives were expressed with the small differentials of vapor quality and temperature. Three-dimensional two-phase thermos-fluid equations were formulated with these derivatives of average specific volume and enthalpy. One-dimensional nozzle flow was calculated with the derived formula. The flow transits from subsonic to supersonic by changing the area ratio.