Heat Transfer Performance Simulation Of Once Through Steam Generator Base On Homogeneous Model

The characteristics of once-through steam generators include high heat transfer coefficient, small heat transfer area and compact structure. It has been applied to integral pressurized water reactor in recent years. The presence of complex phase change at the sencondary side makes heat transfer weakness. Therefore,development a computer code is necessary for once-through steam generator to simulate the thermal-hydraulic characteristics and predict the heat transfer mechanism of dryout accurately.Taken the once-through steam generator of the Babcock&Wilcox Company as the prototype, the fluid is divided into five regions: subcooled water, subcooled boiling, nucleate boiling, liquid deficient, superheated steam base on appropriate heat transfer correlations, and then build the one-dimensional homogeneous flow mathematics model base on distributed parameter method. Computer code is developed in MATLAB and used to analyze influential factors on dryout characteristics.The steady-state simulation results show that the primary side fluid average temperature keeps constant when the once-through steam generator operates under different steady conditions. In low load running, because of subcooled boiling beginning from the entrance,the outer wall of the tube temperature rises rapidly. After boiling reaching the dry out point,the inner and outer wall temperature surges, and the maximum amplitude reaches 22.2 centigrade, heat transfer performance of the secondary fluid is weakened. The length of each heat transfer area in once-through steam generator becomes longer in overheat section and shorter in evaporator section with the load drop.The dynamic-state simulation results show that, when enthalpy and flow rate decreases in the primary side coolant, the degree of superheat of steam also declines, and 5 percent decrease in the enthalpy,the outlet steam can't reach to overheat. Due to the decrease in the feedwater temperature, the inlet fluid is heated up to saturated water rapidly and little influence in the steam outlet temperature. The position of dryout point moves forward and the temperature of steam increased as the feedwater mass flow rate decreased. 30 percent perturbation is given to feedwater mass flow rate, which results in the preheat region disappear. Eventually, the primary side fluid enthalpy is most sensitive to the thermal power of once-through steam generator.To sum up, the simulation on the steady-state and dynamic-state heat transfer performance of once-through steam generator in this paper can analyze operating characteristics easily and predict the dryout phenomenon accurately. It offers a theoretical guarantee to prevent tube rupture and improve safety and reliability of nuclear power equipment.