TRAC-PF1 is modified to include the 3-field governing equations and physical model related to the droplet field. In deriving the present 3-field model, the droplet equation of motion used in the study of Varone and Rohsenow is used to calculate the relative velocity of the droplet and gas. The governing equations and physical models related to the droplet field are based on the 3-field model of COBRA-TF and the finite difference equations of these modified governing equations are derived in the form of TRAC-PF1. New solution matrix elements are derived and these are adopted to the solution step of TRAC-PF1.
The simulation results by the modified code are compared with these from Ishii``s equilibrium entrainment correlation. It is found out that the simulation results depend on inlet void fraction and pipe diameter. When inlet void fraction is 0.9 or higher and the pipe diameter is larger than 3cm, the simulation results approach Ishii``s correlation.