Within the framework of the nuclear reactor safety analysis of pressurised water reactor the flashing flow in pipes and nozzles is examined using a CFD numerical calculation. For the calculation of transient flashing flow a three dimensional CFD model is developed with the aim to predict the propagation of the pressure waves in the two phase flow through the three dimensional geometry. As the most important factor for the modelling of flashing flow, the thermal non-equilibrium between the phases is taken into account. The generation and the propagation of the vapor phase are modelled by conservation equations for the bubble number density according to the model of Jones [1] and mass conservation equations for the vapour phase. The turbulence of the flow is described with the k-ε model. The influence of the dispersed vapor phase on the turbulence is neglected. The system of equations is implemented into the commercial CFD-code CFX4.2. The solution of the system of equations is done numerically with the method of finite volumes. For the verification of the model, calculations of the flow through a converging-diverging nozzle are carried out and the results are compared with experimental ones [2].

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