Numerical Simulation Of MHD Mixed Convection Heat Transfer In Conductive Square Duct Under Inclined Non-uniform Magnetic Field

The liquid metal blanket is a key component with the main roles of energy transfer,tritium breeding and radiation shielding in fusion reactors.Under the actual working conditions,the liquid metal will generate induced current with the action of the applied magnetic field.The action of the current and the magnetic field generates Lorentz force,thus causing the magnetohydrodynamic(MHD)effect in the duct.In addition,the high temperature generated by fusion subject the liquid metal to strong buoyancy force,which causes the liquid metal to develop a complex MHD mixed convection.The MHD mixed convection is the main flow state for the operation of liquid metal blankets.Current studies of blankets are basically based on coplanar magnetic fields.Under the actual working conditions of the Tokamak device,due to the modular structure,the annular magnetic lines intersect the sidewalls of the coolant channels with small angles.The presence of inclined magnetic field changes the flow state of liquid metal.In this paper,the inclined magnetic fields are applied outside a duct to study its effect on the flow stat.In addition,the temperature distribution and the location of the hot spots under the inclined magnetic field affect the range of parameters that can be achieved by the actual blankets and the safety of its operation.It is especially important to study the flow state and heat transfer under the combined action of heat flux and inclined magnetic field to improve the energy conversion efficiency and safety of the actual blankets.Based on the SSTMHD turbulence model developed by the group and the solver developed and verified in Open FOAM,the effects of different inclined angles(α),Grashof number(Gr),Hartmann number(Ha)and Reynolds number(Re)on the velocity distribution,current,pressure drop,temperature distribution and heat transfer efficiency of the duct are investigated in this paper.Firstly,the effect ofαon the flow state and heat transfer efficiency are studied.The results show that the high velocity jets turn toward the core region in the unheated section and the angle is consistent withα.In the heated section,the presence of buoyancy affects the velocity distribution,and the velocity flux is more concentrated on the cold wall.The MHD pressure drop in the heated section of the duct also increases asαincreases.In addition,among the simulated angles,the heat distribution in the duct is more uniform and the maximum Nu exists whenα=30°.Then the effect of Gr on mixed convection heat transfer was investigated whenα=15°andα=45°.The results show that there is a critical Grashof number of 2.88×10~9,A large backflow zone appears near the heated surface when Gr exceeds this critical value.The increase of Gr increases the distribution range of the hot fluid and reduces the heat transfer efficiency.Compared with the result ofα=45°,the dimensionless temperature of the duct is lower atα=15°,and largeαshould be avoided in the design of the liquid metal blankets.Finally,the effect of Ha and Re on mixed convective heat transfer are investigated.It is concluded that the velocity peak in the unheated section increase with the increase of both Ha and Re.In the heated section,increasing Ha can increase the counterflow area and velocity peak near the heated surface,and increasing Re can enhance the strength of convective heat transfer and weaken the lateral heat transfer,resulting in an overall decrease of the fluid temperature and a higher heat transfer efficiency.In addition,increasing either Ha or Re increases the total pressure and the dimensionless pressure drop in the heated section,but Re has a greater effect on the growth of the MHD pressure drop.The above results have important implications for the design of the liquid metal blankets.The range of operating parameters needs to be considered when the magnetic field is inclined.