NUMERICAL SIMULATION OF DRYOUT CHARACTERISTICS OF THE HELICAL ONCE-THROUGH STEAM GENERATOR
Dryout process in the secondary side of a helical once-through steam generator was simulated by using two-fluid three-flow-field mathematical model. The variations of the thermal-hydraulic parameters of the dryout process were analyzed in present work. The results show that dryout location is shifting from the inside into the top of the helical once-through steam generator. With the development of heating, the dryout region gradually extends from local region to the whole cross section of a helical tube. It means that there is a gradual dryout process in the helical tube. The inner wall temperature rises sharply and the variation amplitude of the average inner wall temperature is about 130 K when partical dryout occurs. During the dryout process, the inner wall temperature rises slowly and the liquid temperature maintains the saturated temperature. Meanwhile, the steam temperature rises slowly because of the departure from thermodynamic equilibrium, and the steam begins to be in the superheated condition. The circumferential wall temperature distribution also has a more uniform tend.