Study On Heat Transfer Characteristics And Optimization Of Molten Salt-steam Shell And Tube Heat Exchanger

Energy is an important basis for modern industrial production and development.The development of energy technology determines the development of industrial productivity.However,fossil energy will be exhausted,and people’s demand for renewable energy is higher and higher.As a renewable energy power generation technology,solar photothermal power generation has been widely studied and developed rapidly.As the key equipment of heat transfer in photothermal power generation technology,the performance of molten salt heat exchanger directly affects the operation efficiency of the overall power generation system.Aiming at the problem of large flow dead zone of molten salt in shell and tube heat exchanger,four opening schemes are designed on the baffle to reduce the flow dead zone on the shell side.At the same time,the influence of opening size on the performance of heat exchanger is also studied.The main achievements are as follows:(1)Numerical calculation method is used to simulate the flow state and heat transfer performance of molten salt and water in molten salt steam generator.The size and structure of shell and tube heat exchanger are designed in strict accordance with the national standard(GB/t151).The standard k-ε model is used to simulate the flow and heat transfer of molten salt in the shell side;RPI subcooled boiling model is used to simulate the subcooled boiling of water in the tube side.The reliability of the model is verified by comparing with the experimental data.(2)In order to evaluate the performance of the heat exchanger,the opening scheme is evaluated with the heat transfer factor j,the resistance factor f and the comprehensive performance factor JF considering heat transfer and flow under the same pump power.The results show that the heat transfer factor j decreases slightly,but the resistance factor f decreases greatly,and the comprehensive performance factor JF is greatly improved.Among them,the comprehensive performance of opening scheme 4 is the best,which is 34.6%higher than that without opening.(3)In order to quantitatively evaluate the flow dead zone,the residence time distribution curve is introduced to study the flow state of molten salt.It is found that scheme 4 is the most effective to reduce the flow dead zone,and its volume fraction of flow dead zone is only 31.8%of that without opening.At the same time,under the condition of scheme 4,the heat transfer characteristics of molten salt are studied and its correlation formula is fitted.(4)In order to study the overall performance of molten salt steam generator,its overall reduction is simulated.The effects of operating conditions such as water pressure,water mass flow,molten salt mass flow and molten salt inlet temperature on wall temperature,heat flux and heat transfer coefficient in steam generator are studied,and the causes of these effects are analyzed.(5)The opening diameter of the baffle is optimized by introducing genetic algorithm,and the optimization objectives are heat flux and comprehensive performance factor considering pump power.With the increase of opening diameter,the heat flux first increases and then decreases,while the comprehensive performance factor and the volume fraction of flow dead zone show a monotonic downward trend.