Experimental And Simulation Research On Heat Transfer Characteristic Of High Temperature Molten Salt And Molten Salt Heat Exchanger

High temperature molten salt heat exchanger as an efficient heat transfer equipment has been widely used in the fields of nuclear energy,solar power generation and process heat transfer due to its advantages of high operating temperature,low system pressure and good economic performance.However,molten salt is a new type of heat transfer and storage fluid,there is still a lack of comprehensive and profound understanding on the molten salt heat transfer mechanism and the enhanced heat transfer performance at the present stage.In addition,the high-temperature molten salt heat exchanger has a wide variety of structures and different layouts,resulting in large differences in heat transfer performance.Whether the traditional design process,theoretical calculation methods and simulation analysis of heat exchanger are suitable for high-temperature molten salt,which still needs to be further tested experimentally,especially for the structural thermal design and dynamic operating characteristics of the high melting point salt heat exchanger that is still lack a comprehensive and profound understanding.Based on this,the paper carries out experiments and simulation research on heat transfer characteristics of high-temperature molten salt and molten salt heat exchangers in many high temperature molten salt test loop.The main research work of this paper includes the following three aspects.In the first part of this article,round tube and traverse corrugated tube double-pipe heat exchanger were designed,and the convective heat transfer characteristics and heat transfer mechanism of molten salt were systematically analyzed by the method of combining experiment with theory.Firstly,turbulent experimental data were obtained and were summarized with the different types of molten salt,and further were fitted the correlation formula of molten salt compareing with the traditional classical correlation formula.Secondly,the heat transfer mechanism of molten salt was deeply analyzed.Finally,the enhanced heat transfer performance of molten salt and the traverse corrugated double-pipe heat exchanger were obtained by the comparison with that of round tube heat exchanger.Research shows that(1)The turbulent convective heat transfer characteristics of the molten salt is conform to the traditional empirical correlation and is in good agreement with the experimental results with an error of±20%;(2)The transitional and turbulent flow transition points in the traverse corrugated tube move forward comparing with the smooth tube,which are Re?1300and Re ? 6000 respectively;(3)The heat transfer performance of the traverse corrugated tube heat exchanger is significantly higher than that of the smooth tube and the average thermal performance can be increased by 2.5?2.8 times in transition and turbulence flow.In the second part of this article,a new type of serpentine coil air heat exchanger was designed and developed,and a set of analysis methods for analyzing and calculating a specially designed heat exchanger was established and verified.Firstly,the design method and process of molten salt heat exchanger were introduced.Then,the influence of variable parameters(molten salt temperature,air temperature rise,heat exchange tube diameter)on the structural thermal design were discussed.Finally,experimental research and design verification of the heat transfer performance of the heat exchanger were carried out.In addition,the convective heat transfer law of the shell side air that affects the performance design of the heat exchanger was deeply revealed.The results show that the experimental results are in good agreement with the theoretical design,which verifies the rationality of the theoretical design within the acceptable deviation range of the project.The shell-side heat transfer experiment results are in good agreement with the theoretical formula Zhukauskas,and the maximum deviation is about 5.56%.The results show that the theoretical design method of nitrateair heat exchanger can be applied to guide the engineering design of the same kind of molten salt heat exchanger.In the third part of this paper,the first domestic high-temperature heat transfer performance experiment of fluorine salt heat exchanger was completed,breaking through the current research status of molten salt heat transfer experiments only focusing on low melting point salts such as nitrate and sodium salt,and has certain innovations.The three-dimensional simulation on the full-scale space of the heat exchanger was carried out,and the applicability of the CFD software on the hightemperature molten salt heat exchanger was demonstrated.The structural optimization design and dynamic heat transfer process of the high melting point salt air heat exchanger was comprehensively analyzed.The results show that the simulation results are in good agreement with the experimental results with the deviation within 10%.The simulation analysis can not only reflect the heat transfer law and heat transfer characteristics of the high temperature molten salt heat exchanger,but also provide new ideas for optimized design and safe operation of the high melting point salt air heat exchanger.Based on the above,the heat transfer characteristics of high-temperature molten salt and molten salt heat exchangers has been thoroughly understood,and the understanding of the heat transfer process and mechanism for the molten salt heat exchanger has been improved by means of theoretical thermal analysis,software implementation and numerical simulation.At the same time,the engineering applicability of the theoretical design and analysis software has been also verified.It not only provides theoretical guidance for the engineering design and performance optimization of molten salt heat exchanger,but also provides an efficient solution for its engineering scale design,and also provides new ideas for its application and development in clean energy.