Study On Heat Transfer Characteristics Of Spiral Tube Heat Exchanger For Nuclear Coolant Pump Based On Thermal-Fluid-Solid Coupling

The nuclear reactor coolant pump(RCP)is the heart of the nuclear power plant and the only rotating equipment in the nuclear reactor island,which is required to be able to stably operate without failure for a long time.And it is the only key equipment of the nuclear power system that cannot be independently developed in China so far.The spirally coiled tube heat exchanger is widely used in the RCP with shaft-sealed type because of its advantages such as high efficiency and compactness,high heat transfer performance and not easy scaling.Its heat transfer performance plays a crucial role in the safe and stable operation of the RCP system.Combined with the Science and Technology planning project of Sichuan Province(2017Y0047)undertaken by our university and the project entrusted by a RCP manufacturer,the method of numerical simulation was used to study the flow and enhanced heat transfer performance of the spiral tube heat exchanger under the effect of heat-fluid-solid coupling,and multi-objective optimization design was carried out for the coupled heat transfer of heat exchanger.And then,the triple-indexes evaluation system was built with simultaneously considering the heat transfer,hydraulic loss,and overall heat transfer performance.Multi-objective optimization analysis was carried out on the shell-side Reynolds number,pitch and spiral diameter of the heat exchanger,which established a technical foundation for optimal design of the heat exchanger.The main research and conclusions are as follows:(1)Study on flow heat transfer performance of single-layer spiral tube.The threedimensional model of single-layer spiral pipe with different geometric parameters was constructed and numerical simulation was carried out,and the comprehensive heat transfer performance of the single-layer spiral pipe was analyzed by the correlation performance evaluation coefficient of heat exchanger.It has shown that within the parameters studied in this paper,the diameter of the spiral tube and the mass flow-rate of inlet have significant effects on the heat transfer coefficient of the spiral tube,while the pitch of the spiral tube has little effect.In the evaluation of heat transfer performance of spiral pipe,Nusselt number increases with the increase of Reynolds number,and decreases with the increase of pipe diameter and pitch.The hydraulic loss coefficient and the comprehensive heat transfer performance are negatively correlated with Reynolds number and pitch,and positively correlated with pipe diameter.(2)Study on coupled heat transfer performance of spiral tube heat exchanger for RCP.The flow and heat transfer characteristics of heat exchanger on the tube-side and the shell-side were analyzed under different inlet parameters of the shell-side and geometric parameters of the spiral tube,and the law of flow and strengthening heat transfer performance in the spiral tube heat exchanger were obtained.The research results demonstrated that when the mass flow-rate and temperature at the tube-side are constant,increasing the mass flow-rate at the shell-side,the temperature of the outlet would increase at both the tube-side and the shellside.With the increase of the spiral tube diameter,the outlet temperature of the tube-side increases,while the temperature of the shell-side decreases.At the same time,the shell-side Nusselt number increases with the increase of the shell-side Reynolds number and spiral diameter,the shell-side resistance coefficient decreases with the increase of Reynolds number and tube diameter,and the heat exchanger efficiency decreases with the increase of Reynolds number,while increases with the increase of spiral tube diameter.(3)Multi-objective optimization was carried out for the spiral tube heat exchanger of nuclear coolant pump with coupling heat transfer.Using the Box-Behnken design,the three-factor of shell-side Reynolds number,pitch and spiral tube diameter were designed with three-level.The second-order response models of the three targets of heat transfer,flow resistance and overall heat transfer performance were established based on the response surface method with a goodness of fit.The sensitivities of the three response models were also studied.Finally,the heat exchange performance,resistance performance and the comprehensive heat transfer performance were optimized to obtain the optimum design and process parameters,namely when the shell-side Reynolds number is 13108.436,spiral tube pitch is 16.123 mm and spiral pipe diameter is 10.392 mm of the spirally coiled tube heat exchanger of the nuclear coolant pump,the shell-side higher Nusselt number,low resistance and large comprehensive heat transfer performance can be maintained.It is worth mentioning that the research results of this project have been used in the optimization process of shaft-sealed RCP in the cooperative enterprise and the practical engineering problems have been solved,which proved feasibility and reliability of the research methods and technologies.