| The hot state test is the most direct way to check the actual operating performance of the nuclear pump,but the hot state test is risky and costly.Therefore,in the initial stage of the nuclear pump research and development,the cold state test is usually used to check whether its performance meets the design requirements.Since the physical properties of the test medium are clearly distinguished between cold and hot states,how to use the results of the nuclear pump cold state test to verify the performance of the hot state operation has become a key issue that needs to be paid attention to.In this paper,the whole calculation domain is divided into a hexahedral structured grid,based on the RNG κ-ε turbulence and FLUENT steady calculation,the influence of different physical parameters of the medium in cold and hot states on the hydraulic performance and vibration performance of nuclear pump was researched systematically,and It is expected to provide theoretical guidance for the reliability analysis and hydraulic research and development of the nuclear pump in the hot state.The relative calculation error of the nuclear main pump efficiency in the cold state is 0.87%,and the numerical calculation method adopted basically meets the requirements for calculation accuracy.In order to study the influence mechanism of the change of medium physical parameters on the internal flow characteristics of the nuclear main pump,it is assumed that the density and dynamic viscosity of the medium change gradually at the rate of10%,and the maximum change range is ±20%,and analyzing the influence of the change of medium physical parameters on performance parameters such as head,shaft power and efficiency of the nuclear main pump,and the influence mechanism was also analyzed from the change of internal flow characteristics such as velocity field and pressure field,the results show that within the range of changes set by the research,the changes in density and dynamic viscosity have almost no effect on the velocity field in the nuclear pump,so the head remains basically unchanged;No matter how the density and dynamic viscosity change,as long as the fluidity of the fluid is increased,and the kinematic viscosity is reduced,the pressure difference between the two sides of the blade is correspondingly reduced,the shaft power is correspondingly reduced,and the efficiency is correspondingly improved.In order to study the feasibility of evaluating the thermal performance of the nuclear pump in the cold state test,the clean water at room temperature and liquid sodium at310℃ used as the media respectively,the changes in the hydraulic performance and vibration performance of the nuclear main pump in cold and hot states was analyzed and compared,the results show that the hydraulic performance and vibration performance of the nuclear pump in the hot state are significantly improved than in the cold state,and the efficiency in the hot state is significantly improved.Although the head is slightly reduced,it fully meets the design requirements,and the amplitude of the pressure pulsation is significantly reduced;the hydraulic performance and vibration performance of the nuclear pump obtained based on the cold test can be used as a reliable basis for evaluating the hot operating performance of the nuclear pump.In order to clarify whether the influence of the media physical parameters on the hydraulic performance of the impeller is related to the hydraulic structure of the impeller,the inlet angle and outlet angle of the blade are adjusted at the amplitude of ±2° to change the hydraulic structure of the impeller,the hydraulic performance in the cold and hot state of each scheme was compared and analyzed,the results show that Increasing the blade entrance angle or reducing the blade exit angle within an appropriate range can improve the hydraulic efficiency of the impeller from the perspective of optimizing the flow field structure;no matter how the hydraulic structure of the impeller changes,as long as the kinematic viscosity of the medium is reduced,the hydraulic efficiency of the impeller in the hot state is always higher than that in the cold state,which is the inherent trend of the influence of the physical properties of the medium on the hydraulic performance of the impeller,and it’s nothing to do with the pros and cons of the impeller hydraulic structure.In summary,changes in the physical properties of the medium and changes in the hydraulic structure of the impeller have a certain impact on the hydraulic performance of the impeller,but their action modes are completely different,the change of the physical properties of the medium is achieved by changing the fluidity of the fluid to achieve the impact on the hydraulic performance of the impeller,but it does not change the velocity field structure in the impeller basically;while,the change of the impeller hydraulic structure is achieved by changing the force state of the fluid in the impeller to change the flow field structure to achieve the impact on the hydraulic performance of the impeller,but no matter how the hydraulic structure changes,the hydraulic efficiency in the hot state is always higher than that in the cold state.Since the change of medium physical parameters basically does not change the structure of the velocity vector field in the impeller,its influence on the impeller hydraulic design theory can be ignored in the process of impeller hydraulic optimization. |
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