Research On Dynamic Simulation And Cooling Characteristics Of Cooling Tower In Nuclear Power Plant

Unlike open-loop mode adopted in the circulating coolant system of coastal nuclear power plant, the circulating coolant system of inland nuclear power plant generally adopted cooling tower closed water supply mode,the ambient atmosphere is the ultimate heat sink.Dynamic response of heat and mass transfer in cooling tower would affect the inlet coolant water temperature of condenser, which influences efficiency and safety of nuclear power plants. Currently, the analysis and calculation of cooling tower were concerned about steady-state conditions, through analyzing the relationship between the structure and design performance to optimize the design of cooling tower. The research on real-time dynamic simulation for analyzing operating characteristics has not been discussed yet. The transient simulation of cooling tower can improve the safety of inland nuclear power under accident conditions; therefore it has immense engineering and theoretical significance.This thesis focused on the natural draft counter-flow wet cooling tower. Through the analysis of the heat and mass transfer and following process in the cooling tower in detail, the dynamic mathematical and physical model of the flow of air and coolant water, and the heat and mass transfer model between air and coolant water which based on the Merkel's model were established. The air flow field was assumed as two-dimension axial symmetric incompressible flow. Finite volume method and SIMPLE algorithm were adopted to solve the two-dimensional Navier-Stokes equations. The water flow field was assumed as one-dimensional flow, with classical fourth-order Runge-Kutta algorithm to solve one-dimensional ordinary differential equations.The simulation code was developed and debugged by Fortran program language. The operating parameters of a certain 600MW power plant were taken as an example, and the comparison was made between calculated data and measured data of outlet water temperature to verify the validity of both the model and code. On the basis, a particular ambient condition was selected to analyze the distribution of velocity, temperature and moisture content of air flow field, and the temperature distribution of both coolant water flow field and each feature surface under two different operating conditions. One condition is that the distribution of spray water rate is uniform,and the other condition is that the distribution of spray water rate is linear along radial direction. Then,the influences of inlet water temperature, inlet circulating coolant water flow, inlet air humidity and inlet air temperature on outlet water temperature were studied in this paper. Finally, the transient response curves of outlet air temperature and outlet coolant water temperature were given when the inlet coolant water temperature or coolant water flow were changed under the variable conditions or accident conditions. Thus, this paper provided further basis for the design and operation of cooling tower in inland nuclear power plant.