| Once-through steam generator(OTSG)is an important equipment of integral pressurized water reactor and function as the hinge of the primary loop and the secondary loop.Driven by the feed pump,the secondary feed water of the OTSG flows through the heat transfer tube where it is heated by the primary coolant.Then it passes through the supercooling section,saturation section and superheating section sequentially,and finally is transformed into superheated steam.The operating rules and control methods of OTSG are different from natural circulation steam generators,and need to be further studied.Due to the complicated two-phase flow and heat transfer phenomenon of the secondary side of OTSG,it is necessary to develop accurate and efficient simulation models and solving programs to accurately simulate its physical process and study its operating characteristics.Based on the fixed control volume method,this paper develops a precise OTSG simulation model and solving program concerning its particular structure and operating characteristics of the OTSG in concentric annuli tube.The basic model was built upon the one-dimensional twophase drift flow equation(five equations).Through research on literature of this area,the existing models were adjusted to fit into with the narrow annular channel of OTSG.These newly-built auxiliary models are as follows: a friction drag coefficient model,a convective heat transfer coefficient model and a net vapor generation model,etc.All in all,these models were developed for the particular structure of the narrow annular channel,taking into account possible two-phase flow patterns and heat transfer modes.The basic equation is discretized in a semi-implicit format,and the pressure-velocity in the equation is decoupled to obtain a sparse matrix equation about the pressure.After analyzing the structure of the sparse matrix equation,the coefficient matrix of the pressure matrix equation is automatically generated by the program developed in this paper according to the topological relation of the control volume and the connection pipe.This coefficient matrix is a symmetric sparse matrix,therefore,the complete pivoting of gaussian elimination is used to solve the sparse matrix equation.Finally,a precise simulation program of OTSG in concentric annuli tube model is developed by FORTRAN language and then modularly packaged by the interface variable for data exchange with the first and second loop systems.In order to quickly set up the simulation models,C# window interface is developed in this paper which consider the actual structure of the once-through steam generator.Then the simulation models can quickly be set up by geometric parameters and the number of control volume.Taking an OTSG in concentric annuli tube with a load of 3MW as an example,the developed program is used to perform steady-state and dynamic simulation.First,the sensitivity analysis of simulation control volume is performed.Then,the steady simulation results are compared with the design parameters,and the main parameter error is controlled within 1%.After comparing the dynamic simulation results with the simulation results of the RELAP5 program,the variation tendency of the results remains consistent.Moreover,this program can achieve accurate simulation of different heat exchange modes such as subcooling water,subcooling boiling,nucleate boiling,transition boiling,film boiling and full flow patterns such as bubble flow,bullet flow,annular flow,and diffuse flow at secondary side.All these results demonstrate the accuracy of the developed OTSG simulation program.In conclusion,the OTSG simulation program developed in this paper is of significance in engineering practices since it provides tools for further research of OTSG operation characteristics,and also a reference for future development of real-time simulation models and programs of integrated reactor. |
