Abstract
The valve used in nuclear power plant must be qualified but the limitation of the test facility leads to use the numerical analysis. The flow coefficient is calculated with the consideration of the pressure, velocity and geometry. And the flow coefficient is the important physical property which is prepared using experiment or analysis by valve manufacturer. In this study, the analysis model was made according to ISA 75.02.01 and the mass flow rate and pressure drop ratio was calculated. The model of the expansion factor was applied to the simulation result and the pressure drop ratio at the start of the choked flow in the valve was found. With the simulation result, the consideration was performed that the expansion factor is the important physical property to the system engineer in addition to the flow coefficient.