Numerical Simulation Of Geometry Sensitivity And Heat Transfer In MHD Rectangular Duct Flows

Nuclear energy based on controlled nuclear fusion is regarded as ideal energy to solve the energy crisis and environmental issues.The application of a thermonuclear fusion reactor is one of the main ways to achieve controlled nuclear fusion.As a key component of the thermonuclear fusion reactor,the blanket mainly plays the role of transporting fusion energy,breeding tritium,and shielding radiation.The liquid metal blanket has advantages over the other type of blanket.Reduction of pressure drop and enhancement of heat transfer remain key issues in the application of liquid metal blankets.The geometry sensitivity of magnetohydrodynamic(MHD)duct flows is found in research.In other words,the shape of the duct cross-section affects the velocity distribution,pressure drop,and heat transfer in duct flows,which may provide a new approach to solving the problems of pressure drop and heat transfer and can be referenced in the liquid metal blanket design.In order to investigate the effects of geometry sensitivity on MHD rectangular flows,two geometry variations are conducted in this thesis compared with the ordinary electrically conducting square duct.One of the geometry variations is to change the aspect ratio of the duct cross-section.The aspect ratio is defined as the ratio of the Hartmann wall length to the side wall length.The other is to add several pairs of triangular strips(TS)on the opposite walls of the duct.Laminar flows in the conducting rectangular ducts with the above geometry variations are numerically simulated using an in-house MHD solver based on low magnetic Reynolds numbers developed in OpenFOAM.In this thesis,the effects of aspect ratio on the velocity distribution,pressure drop,and heat transfer of MHD flows in the electrically conducting rectangular ducts are studied firstly.The results show that the maximum velocity of the side-layer velocity jet grows as the Hartmann number is fixed,and the aspect ratio increases.Besides,the MHD pressure drop and the Nusselt number increase as the aspect ratio increases when the Hartmann number is relatively large.Considering the reduction of pressure drop,the aspect ratio of the rectangular duct is suggested to be smaller within a reasonable range.While considering the enhancement of heat transfer,the aspect ratio is suggested to be larger within a reasonable range.Therefore,there is actually an optimization problem to be solved in the design of the aspect ratio,and it is necessary to balance the pressure drop and heat transfer.Moreover,MHD flows in ordinary conducting rectangular ducts(R-duct),and conducting rectangular ducts with the TSs on the opposite walls(RTS-duct)subjected to a uniform magnetic field are simulated.Furthermore,comparing the results of pressure drop and heat transfer in the RTS-ducts under the uniform magnetic fields along two directions,the suggestion on the TSs is given.The results show that a bit lower pressure drop and larger Nusselt number are observed in the RTS-duct with the TSs on the Hartmann walls,compared with the one with the TSs on the side walls when the Hartmann number is relatively large.Moreover,it is a favorable trend that the absolute value of the relative difference of pressure drop and the relative difference of the Nusselt number increase as the Hartmann number increases.Therefore,it is better to attach the TSs to the Hartmann walls of the rectangular duct.When the TSs are on the Hartman walls,considering the velocity distribution,pressure drop,and heat transfer,the RTS-duct has an advantage over the R-duct.Furthermore,taking the pressure drop and heat transfer into accounts,the numbers of TSs are suggested to appropriately increase on the Hartman walls of the RTS-duct.Numerical simulations of laminar flows in electrically conducting rectangular ducts with different aspect ratios and with TSs on the opposite walls are performed in this thesis.The effects of geometric sensitivity based on the above two geometry variations on the velocity distribution,pressure drop,and heat transfer of MHD duct flow are investigated.The simulation results provide a reference to the geometry design of the liquid metal blanket.