Research On The Differences Of Heat Transfer In Natural Circulation Of Different Fluids

Natural circulation has a very broad application prospect in reactor safety,as well as other industries.Research on the difference of heat transfer in natural circulation of different fluids,especially on certain thermal parameters,has great significance to improve the reactor safety.It can provide a reference for the selection of coolant in the design of the new reactor,and can also be used as a guide for the mitigation of the accident.Therefore,it is important to study the difference of heat transfer in natural circulation of different fluids.By the methods of ANSYS-CFX simulation and programming,effects of heating power,system pressure and inlet temperature on the heat transfer of water,lead bismuth and liquid sodium in natural circulation loop have been studied.With the increase of heating power,both exit temperature of heating section and flow rate of different fluids are improved.The heat transfer coefficient of different states of water and lead bismuth increases,while that of the liquid sodium decreases.With the increase of pressure,the outlet temperature and flow rate of supercritical water changes varies substantially,while that of subcritical water,lead bismuth and liquid sodium changes little.The heat transfer coefficient of water increases first and then decreases with the increase of pressure,while that of lead bismuth and liquid sodium is less affected by pressure.With the increase of the inlet temperature of the heating section,the outlet temperature of different fluids is increased,except for liquid sodium.The flow rate of water increases while that of liquid sodium decreases.The flow rate of lead bismuth increases firstly and then decreases.Calculation results are compared with the experimental data of our own and other researches,which proves the accuracy of the calculation results.Based on the calculation results,the difference of heat transfer in natural circulation of different fluids is studied.Using gray correlation analysis method,the reasons for the difference are proposed.The result shows that the effects of different thermal parameters on the outlet temperature of different fluids are approximately equal,while the heating power has a great influence on the outlet temperature of supercritical water.The system pressure has negative impacts on the flow rate of supercritical water,which influences supercritical water most.Compared with water,liquid metal is hardly affected by system pressure.The effects of different thermal parameters on the heat transfer coefficient of different states of water and lead bismuth are approximately equal.Compared with other fluids,these thermal parameters have little effect on heat transfer coefficient of liquid sodium.This is mainly caused by the difference of physical properties of different fluids.Considering the characteristics of flow and heat transfer,liquid sodium has the best heat transfer characteristics,followed by lead bismuth,supercritical water and supercritical water.Under the same boundary conditions,the heat transfer coefficient of liquid sodium is higher than that of other fluids,and the circulating flow rate is also at a high level.The heat transfer characteristics of liquid sodium are affected little by different thermal parameters.