Influence of variation of pipe diameter on pressure drop predictions of the new modified three-fluid model inside condensing vertical pipes

When a loss of coolant accident occurs in the primary system of a water-cooled nuclear reactor, a large amount of steam is released into the reactor containment. Therefore, there is the possibility of over-pressurization of the reactor containment. In such a condition, the released steam is often condensed using a passive containment cooling system. This system consists of condensing vertical pipes with diameters of 30–50 mm. Thus, condensation inside vertical pipes with annular flow happens, which is usually analyzed using the three-fluid models. In the present work, the effect of variation of condensing vertical pipe diameter on pressure drop predictions in downward condensing annular flow of steam is studied using the new modified three-fluid model. In a new pipe diameter, D = 0.03 m, the pressure drops are calculated using the new modified three-fluid model and the correlation of Stevanovic et al. for steam–liquid film interfacial friction coefficient and compared.