| Liquid metal has the advantages of high thermal conductivity and high specific heat capacity.The liquid metal blankets have the advantages of simple structural design,easy propagation and extraction.Therefore,the liquid metal blanket is one of the TBM(Test Blanket Module)design schemes.Liquid metal flows in duct subjected to an external magnetic field will produce a larger MHD pressure drop than the general hydraulics due to the magnetohydrodynamic(MHD)effect,and redistribute the flow field in the duct.The nuclear fusion blanket is under the complex environment of magnetic-thermal-fluid-solid multi-coupling field,so the flow state of metal fluid moving in the complex blanket ducts structure will be more complicated.Duct geometry,wall conductance ratio,Reynolds number and Hartmann number all have an effect on the MHD effect.Therefore,the study of the wall conductance ratio on the flow state of metal fluid flows in the complex blanket structure and the heat transfer characteristics of the duct under the external heat source has important reference value for the TBM design scheme.Numerical simulation is an important method in the study of MHD flow.In this paper,the complex blanket duct structure is numerically analyzed by using the fluid-solid coupled low-magnetic Reynolds number MHD solver independently developed based on the open-source CFD OpenFOAM environment.Firstly,the numerical simulate of the conducting rectangular duct with asymmetric wall conductance ratio distribution is investigated.It is found that when the wall conductance ratio of the solid wall at the side of the parallel layer is asymmetrically distributed,the velocity jets in the parallel layer of the flow cross section are also asymmetrically distributed,and the strength of velocity jet decreases with the increase of the wall conductance ratio.The dimensionless pressure gradient increases with the wall conductance ratio and the cross-sectional aspect ratio along the center flow of the duct.Furthermore,the characteristics of liquid metal flows in a conducting U-turn rectangular duct subjected to an external uniform magnetic field is numerically analyzed.The U-turn rectangular duct includes five parts:the duct wall,partitioning wall,inflow channel,outflow channel and connecting channel.The influence of different wall conductance ratio of the duct wall and the partitioning wall on the flow velocity,induced electric current,electric potential,and pressure drop distribution are investigated.When the duct wall is insulating and the partitioning wall is weak conducting,the flow forms a velocity vortex at the end of the partitioning wall because of the strong back pressure gradient in the outflow channel.With the increase of Hartmann number,the velocity vortex area decreases continuously,and the pressure fluctuation in the connecting channel becomes more intense and spreads to the inflow and outflow channel respectively.When the duct wall is weak conducting,a high-velocity jets form in the side layer on both sides of the partitioning wall and the velocity distribution is extremely asymmetric.The pressure gradient is two orders of magnitude higher than that of cases with the insulated duct wall,and the wall conductance ratio of the partitioning wall significantly affects the pressure drop along the flow direction.That is to say,the wall conductance ratio of the duct wall and the partitioning wall all have impact on the MHD flow,and the conductivity of the duct wall plays a decisive role in the distribution of the pressure drop in the conducting U-turn rectangular duct.Based on the flow field of the U-turn rectangular duct with different wall conductance ratio distributions,the heat transfer efficiency of the duct are also different when the external heat source is applied to the different side of the duct wall.When the heat source is located at the side of the inflow channel duct wall,the duct wall and the partitioning wall all conducting duct structure has the best heat transfer effect.When the external heat source is added to the duct wall side in the same or opposite direction as the magnetic field,the U-turn rectangular duct with the duct wall conducting and the partitioning wall insulating has the best heat transfer efficiency.In this paper,the characteristics of the fluid velocity,induced electric current,electric potential,pressure drop distribution along the flow direction and the heat transfer of the duct are numerically distributed by changing the wall conductance ratio,Hartmann number,Reynolds number and the position of the external heating source on different side of the duct wall.The results of the numerical simulation provide important technical experience and experimental data support for the design and development of future blanket. |
