Session: 15-06

Paper Number: 134834

134834 - Transport Characteristics of Two-Phase Flow in Rod Bundle Channels With a Spacer Grid 

Abstract: 

Gas-liquid two-phase flow appears widely in the fields of energy, chemical, and machinery industries. In the pressurized water reactor, to improve the heat transfer capacity between the coolant and the fuel assembly, subcooled boiling is allowed in the core under normal operating conditions. Furthermore, when a loss of coolant accident (LOCA) occurs, the heat exchange capacity is greatly weakened, and the core temperature increases. In order to prevent further deterioration of the heat exchange and the fuel cladding meltdown, the emergency core cooling (ECC) system injects emergency cooling water into the core. During this process, a two-phase flow will exist in the reactor or heat exchanger.

The heat and mass transfer of the two-phase flow is mainly through the gas and liquid interface. Due to the effects of pressure, phase change, convection, and local effects, the shape and scale of the interface will change with the flow, resulting in changes in parameters such as void fraction, interfacial area concentration, and interphase drift velocity, thereby affecting heat and mass transfer between two phases and interphase resistance characteristics. Therefore, it is necessary to carry out experimental research on the phase distribution characteristics in rod bundle two-phase flow under simulated reactor accident conditions.

To further elucidate the distribution characteristics of interfacial structure parameters such as void fraction and interfacial area concentration in rod bundle channels, this study investigates the air-water two-phase flow in the 5 × 5 rod bundle channels using a prototype spacer grid. The local distribution of phase interface flow parameters such as void fraction, interfacial area concentration, bubble velocity, and Sauter mean diameter were measured using a four-sensor conductivity probe at different height sections in the flow direction.

The one-group interfacial area transport equation applicable to rod bundle channels is established. The sink and source terms such as the random collision (RC) between bubbles, the wake entrainment (WE) process, and the breakup due to the turbulent impact (TI) are considered in the IATE model. And the calculation accuracy of this model is about 15%, which can achieve the exactitude requirements of the one-dimensional thermal hydraulic programs.

The results reveal that the radial distribution of the phase interface parameters is mainly affected by the combined effect of lateral forces such as lift force, wall lubrication force, and turbulent dispersion force. The spacer grid mainly affects the distribution characteristics of phase interface parameters through turbulent vortex aggregation and grid shear fracture, turbulent vortex enhances bubble coalescence and grid shear enhances bubble breakup. There is a pressure drop zone downstream of the spacer grid, and the distribution of interfacial parameters inside it undergoes drastic changes. This study provides a reference for optimizing two-phase flow phase interfacial transport models for rod bundle channels.

Presenting Author: Jiaxing Ren Harbin Engineering University

Presenting Author Biography: Jiaxing Ren is a PhD student at Harbin Engineering University, his major is reactor thermal hydraulics and two-phase flow measurement and modeling.

Authors:

Jiaxing Ren Harbin Engineering University
Ruohao Wang Harbin Engineering University
Fangdong Wang Harbin Engineering University
Shouxu Qiao Harbin Engineering University
Sichao Tan Harbin Engineering University
Ruifeng Tian Harbin Engineering University
Puzhen Gao Harbin Engineering University