Numerical Simulation Of Mixed Convective Heat Transfer Of MHD Flow In An Electrically Conducting Square Duct

The blanket is a key component in the conversion of controlled thermonuclear fusion reaction energy into thermal energy.The main functions of the liquid metal blanket include heat extraction,tritium breeding and shielding radiation.With an applied magnetic field,strong magnetohydrodynamic effects exists in the flow of liquid metal within the blanket.As a common model for blanket studies,the magnetohydrodynamic effects of the electrically conducting square duct magnetohydrodynamic flow are:(1)MHD pressure drop well above the normal hydrodynamic pressure drop normal fluid pressure drop,(2)the suppression of magnetohydrodynamic turbulence,and(3)the typical "M-shaped" velocity profile.The Reynolds number,Hartmann number,Grashof number,wall conductance ratio,and the aspect ratio of the duct cross-section are closely related to the magnetohydrodynamic effect,and it is important to study the relationship between the above dimensionless parameters and the magnetohydrodynamic effect in the duct to reduce the magnetohydrodynamic pressure drop of the liquid metal in the blanket and improve the thermal properties of the blanket.Firstly,the MHD fluid quasi-two-dimensional turbulent flow is studied,and the numerical simulation of the MHD fluid duct flow in an electrically conducting square duct is carried out with an applied transverse uniform magnetic field.The quasi-two-dimensional turbulent flow with partial detachment of jets from the side wall is reproduced,and the distribution of velocity and vortex structure in the duct when partial detachment of jets from the side wall,focusing on whether the quasi-two-dimensional turbulent flow induced by secondary flow can reduce the magnetohydrodynamic pressure drop.It is found that the quasi-two-dimensional turbulent flow can effectively reduce the magnetohydrodynamic pressure drop at a large wall conductance ratio.Then,the MHD fluid mixed convection heat transfer of a horizontally placed electrically conducting square duct is simulated numerically in two cases: the magnetic field direction is perpendicular and parallel to the temperature gradient direction.The effects of wall conductance ratio and Graschof number on the velocity,temperature,heat transfer efficiency,and pressure drop of magnetohydrodynamics in the duct were investigated.The results of the study under the condition of perpendicular magnetic field and temperature gradient show that the effect of wall conductance ratio on mixed convection heat transfer in laminar flow condition is limited,while the effect of Grashof number on mixed convection heat transfer is closely related to the critical Grashof number.When the Grashof number is greater than the critical value,the strong buoyancy force causes the formation of a transverse circulation in the duct with significant effects on velocity and temperature distribution,while causing the heat transfer efficiency in the duct to increase.The results of the study with the perpendicular magnetic field and temperature gradient show that the wall conductance ratio has similarly little effect on the flow as well as on the heat transfer efficiency.On the other hand,the fluid in the duct is more suppressed by the magnetic field under this condition than when the magnetic field is perpendicular to the temperature gradient,resulting in no transverse circulation in the simulated parameter range,so the velocity,temperature,heat transfer efficiency,and pressure drop in the duct do not change significantly as the Graschof number increases.