Research On Evolution Characteristics Of Flow And Thermal Fields Of Nuclear Main Pump Canned Motor With Spiral-Wound Heat Exchanger Under Multiple Operating Conditions

The canned motor of the nuclear main pump owns the sole active component within the primary loop of a nuclear reactor,it serves as the "heart" of the nuclear power plant,requiring safe and stable operation for 60 years.Since its specific thermal safety requirements and cooling structure features,the Taylor-CouettePoiseuille flow and convection heat transfer mechanisms within the narrow gaps of the canned motor,the coupled heat transfer mechanisms between cooling water and solid components,and the evolution law of stable and transient temperature rise have become key scientific issues in the research of thermal problems related to such motors.This study mainly takes the canned motor of small reactor main pumps of newly developed external spiral heat exchanger as the research object,the research concerning with temperature numerical prediction methods for fluid-solid coupling under multiple operating conditions,flow and thermal fields under rated conditions,key influencing factors of temperature rise of motor,and evolution law of temperature rise during scenarios like secondary water supply outage and power outage conditions(outage of power in the plant)are conducted.In response to the current temperature numerical prediction methods for temperature rise of canned motor,where primary water is in a non-closed loop state and it is difficult to achieve continuous temperature evolution of primary water and solid components in the motor over time under transient fault conditions,a fluidsolid coupled temperature numerical prediction method for heat transfer and flow in the canned motor under rated conditions,secondary water supply outage,and power outage fault conditions is proposed.A physical model of the canned motor and threedimensional mathematical model for turbulence flow and heat transfer have been established.Using UDF secondary development,is implemented to achieve a closedloop primary water circulation as well as mathematical description and loading of complex and variable boundary conditions.Additionally,the thermal properties of the cooling water and main solid components are considered as a function of pressure and temperature.The methodology encompasses the description of the testing platform and the identification of temperature measurement points.Furthermore,a thermal safety evaluation index has been formulated.This comprehensive approach lays the theoretical foundation and temperature numerical prediction method for subsequent calculations and analyses involving stable and transient operating conditions.A temperature numerical prediction study on coupling fluid-solid of flow and heat transfer is conducted for cold-state rated conditions of the canned motor.The pressure,velocity,and temperature distribution characteristics of the relative reference point of both primary and secondary cooling water are obtained,revealing the distinctive temperature distribution characteristics.A thorough investigation is performed to the temperature rise characteristics of the Taylor-Couette-Poiseuille flow of primary cooling water in the narrow gap of the motor.The findings indicate that the temperature gradually increases along the axial direction of the motor from top to bottom.It is revealed that the stator and rotor clearance is the main heat exchange area inside the motor,and the influence of the high temperature coolant below on the primary water temperature rise of the motor exceeds 17.03 % in the stator and rotor clearance area.The convective heat transfer coefficient of the stator and rotor side gradually decreases from top to bottom along the axial direction.The simulation results are then compared with experimental data to confirm the accuracy of the proposed three-dimensional steady-state fluid-solid coupling temperature field prediction method.On the basis of the research on the flow and thermal fields under cold-state rated conditions,in order to address the main influencing factors of motor temperature rise,the error caused by SST k-ω two-equation turbulence model is smallest and is most suitable model for the turbulent state of Taylor-CouettePoiseuille flow inside the motor.A method for solving the inverse heat transfer problem to determine the thermal property parameters of solid components is provided.The values for determining the equivalent insulation of the winding and the axial thermal conductivity of core lamination are obtained.The relationship between the peak temperature of the stator winding insulation and the temperature of the lubricating water measuring point of the lower guide bearing and the influencing factors such as equivalent insulation thermal conductivity,axial thermal conductivity of core lamination,secondary water inlet temperature,secondary water inlet velocity,composite heat transfer coefficient and ambient temperature is clarified.These findings reveal the main mechanisms and influencing factors of motor temperature rise,providing a theoretical foundation for the regulation of motor winding and primary and secondary water stable and transient temperature field.Building upon the aforementioned research,a study is conducted on the transient scenario of a sudden secondary water supply outage fault during the coldstate rated conditions of the canned motor.The transient flow and temperature field distribution characteristics of both primary and secondary cooling water in the motor,and the transient temperature rise evolution law of both cooling water and main solid components are investigated using the three-dimensional transient fluid-solid coupled temperature numerical prediction approach.The evolution law of temperature of both primary and secondary cooling water and solid components inside the motor continuously increasing with the increase of secondary water supply interruption time has been revealed.The proposed method is used to predict the flow and temperature field when the secondary water supply outage fault under the thermal rated condition,and it is determined that the temperature of the stator winding and the lower guide bearing is in the thermal safety state.The simulation and predict temperature results are then compared with experimental values to verify the accuracy of the proposed transient temperature field prediction simulation method.Focusing on the scenario of a sudden power outage fault during the hot-state rated operating conditions of the canned motor,a fluid-solid coupled temperature numerical prediction approach is employed to study the coupled heat transfer mechanism between primary and secondary cooling water,the solid components within the motor and evolution law of temperature rise.It is found that the temperature of cooling water and solid components tends to be uniform.The primary water temperature rise rate of the upper circulation loop is low,and the lubricating water temperature rise rate of the lower guide bearing is large in the early stage,and then gradually slows down.A comparative thermal safety evaluation is conducted under multiple operating conditions,identifying the motor casing as the location prone to thermal stress-related faults.