Liquid Metal Magnetohydrodynamic Flows Research Articles

Numerical simulations of 3D magnetohydrodynamic flows in dual-coolant lead lithium blankets

In the dual coolant lead lithium blanket (DCLL) the liquid metal PbLi is used as coolant to remove the volumetrically generated heat. This requires higher flow velocities than in separately cooled blanket concepts, where the liquid metal serves exclusively as breeder, neutron multiplier and shield against high neutron radiation. The relatively fast movement of the electrically conducting fluid in the strong magnetic field confining the fusion plasma induces electric currents, which are responsible for strong Lorentz forces, high magnetohydrodynamic (MHD) pressure drop, and substantial modifications of velocity profiles compared with hydrodynamic flows. In order to support the design activities of a DCLL blanket, 3D numerical MHD simulations for one column of such a blanket module have been performed. The simulations take into account, that currents may close along the inner conducting sheet of sandwich-type flow channel inserts that are foreseen for pressure drop reduction. The applied numerical code has been carefully validated. It applies for magnetic fields of arbitrary orientation and is capable of simulating the liquid metal MHD flow in the blanket in the parameter range relevant for fusion applications.

Experimental study of liquid metal magnetohydrodynamic flows near gaps between flow channel inserts

The flow of the electrically conducting lead lithium, foreseen in liquid metal blankets as breeder and coolant, under the influence of the plasma-confining magnetic field induces electric currents that create strong electromagnetic Lorentz forces and high magnetohydrodynamic pressure drop. Electrically insulating flow channel inserts (FCI) may be applied for electrically decoupling the liquid metal flow from the well-conducting channel walls. This reduces currents and associated Lorentz forces that are responsible for the major contribution to pressure drop in the blankets. For fabrication reasons, it is unavoidable that gaps between inserts are present. Gaps will interrupt the electrical insulation, thus providing unwanted local short circuit for electric currents. For experimental investigations of 3D effects at junctions of FCIs, a test section has been manufactured and experiments have been performed in the MEKKA facility at the Karlsruhe Institute of Technology (KIT). The present experimental study shows the benefits of FCIs for pressure drop reduction in fully developed flows and quantifies the deterioration of pressure drop reduction by the presence of uninsulated gaps between FCIs.

Numerical analysis of a magnetohydrodynamic duct flow with flow channel insert under a non-uniform magnetic field

This study performs a numerical analysis of three-dimensional liquid metal (LM) magnetohydrodynamic (MHD) flows in a square duct with an FCI in a non-uniform magnetic field. The current study predicts detailed information on flow velocity, Lorentz force, pressure, current and electric potential of MHD duct flows for different Hartmann numbers. Also, the effect of the electric conductivity of FCI on the pressure drop along the main flow direction in a non-uniform magnetic field is examined. The present study investigates the features of LM MHD flows in consideration of the interdependency among the flow variables.

Magnetohydrodynamic pressure drop and flow balancing of liquid metal flow in a prototypic fusion blanket manifold

Understanding magnetohydrodynamic (MHD) phenomena associated with the flow of electrically conducting fluids in complex geometry ducts subject to a strong magnetic field is required to effectively design liquid metal (LM) blankets for fusion reactors. Particularly, accurately predicting the 3D MHD pressure drop and flow distribution is important. To investigate these topics, we simulate a LM MHD flow through an electrically non-conducting prototypic manifold for a wide range of flow and geometry parameters using a 3D MHD solver, HyPerComp incompressible MHD solver for arbitrary geometry. The reference manifold geometry consists of a rectangular feeding duct which suddenly expands such that the duct thickness in the magnetic field direction abruptly increases by a factor rexp. Downstream of the sudden expansion, the LM is distributed into several parallel channels. As a first step in qualifying the flow, a magnitude of the curl of the induced Lorentz force was used to distinguish between inviscid, irrotational core flows and boundary and internal shear layers where inertia and/or viscous forces are important. Scaling laws have been obtained which characterize the 3D MHD pressure drop and flow balancing as a function of the flow parameters and the manifold geometry. Associated Hartmann and Reynolds numbers in the computations were ∼103 and ∼101-103, respectively, while rexp was varied from 4 to 12. An accurate model for the pressure drop was developed for the first time for inertial-electromagnetic and viscous-electromagnetic regimes based on 96 computed cases. Analysis shows that flow balance can be improved by lengthening the distance between the manifold inlet and the entrances of the parallel channels by utilizing the effect of flow transitioning to a quasi-two-dimensional state in the expansion region of the manifold.

Development of combined temperature – Electric potential sensors

Thermohydraulic measurements in liquid metal test blanket modules for ITER require reliable sensors for detection of temperature and magnetohydrodynamic properties of the flow such as the distribution of electric potential. The latter one can be directly compared with numerical simulations or interpreted in terms of local liquid metal flow rates. Combined temperature-potential probes may serve for both purposes for sensing temperature and potential values, while remaining relatively small in size. By comparison with results obtained using other sensing techniques or theoretical results, the present paper confirms that such measurements in magnetohydrodynamic liquid metal flows may yield accurate data for potential.

Effect of the spatial change in the electric conductivity of the sub-channel walls on the imbalance of MHD flows

This numerical study analyzes the characterisitics of three-dimensional liquid metal (LM) magnetohydrodynamic (MHD) flows, with combined internal heat generation and wall heat transfer, in a manifold under a uniform magnetic field by using commercial code CFX. The current study investigates the effect of the distribution of the electric conductivitity of the duct walls on the flow imbalance among the sub-channels in the manifold system made up of three sub-channels. In the manifold, the uniform heat generation in the fluid stream and the uniform heat flux on one side wall (parallel to the magnetic field) are applied. Here, the mechanism causing the imbalance in mass flow rate (and in energy flow rate) is clearly discussed. In the fluid region surrounded by the walls with lower electric conductivity, a large electric potential difference and higher velocity are obtained, causing a high mass flow rate and energy flow rate therein, allowing an effective cooling in regions with higher heat load in the blanket. In addition, the interdependency of the current, electric potential, velocity, pressure gradient and temperature of LM MHD flows in the manifold is described in detail.

Effects of Hartmann number and conductance ratio on the flow imbalance in merging ducts with locally different electric conductivities

In this study, examined are three-dimensional Liquid metal (LM) Magnetohydrodynamic (MHD) flow and convective heat transfer in merging ducts with locally different electric conductivities, having two inlets and one outlet, under a uniform magnetic field. Computational fluid dynamics simulations are performed to predict the behavior of the MHD flows in the ducts. Though numerous analytic, experimental and numerical studies on LM MHD duct flows were performed, detailed flow characteristics of a LM MHD flow in a merging duct with locally different electric conductivities have rarely been studied. In the present study, the interdependency of the current, fluid velocity, pressure, electric potential is examined in order to describe the electromagnetic characteristics of the liquid-metal flows in merging ducts. Here, cases with various arrangements of the electric conductivity in two inflow channel walls are considered for different Hartmann numbers, yielding different distributions of the fluid velocity in different cases, which leads to the imbalance of mass flow rate in the inflow channels, allowing differential cooling in a liquid metal cooling system of a fusion reactor.

Numerical analyses on liquid-metal magnetohydrodynamic flow in sudden channel contraction

ABSTRACTThree-dimensional numerical calculations have been performed on the magnetohydrodynamic (MHD) flows through a rectangular channel with sudden contraction, particularly in order to estimate the pressure drop through the sudden contraction. The sudden contraction is in the directions both perpendicular and parallel to the applied magnetic field. The Hartmann number, the Reynolds number, and the magnetic Reynolds number were set to ∼100, ∼1000, and ∼0.001, respectively, in simulating laboratory conditions. The continuity equation, the momentum equation, and the induction equation were solved numerically. In the sudden contraction in the direction perpendicular to applied magnetic field, the loss coefficient takes a positive value in all the cases performed in this study, contrary to the expectation. This result is in contrast to that in the sudden expansion in the direction perpendicular to applied magnetic field, where the loss coefficient generally takes a negative value due to the MHD effect. In the sudden contraction in the direction of applied magnetic field, the loss coefficient takes a positive and large value in all the cases performed in this study. The loss coefficient generally becomes larger than that in the case of corresponding channel expansion in the direction of applied magnetic field.

Magnetohydrodynamic flows in u-shaped ducts under a uniform transverse magnetic field

In this study, the three-dimensional liquid metal (LM) magnetohydrodynamic (MHD) flows in a u-shaped duct under a uniform magnetic field applied perpendicular to the flow plane are numerically analyzed with the use of commercial software CFX. The u-shaped duct system is made up of an inflow channal, an outflow channal and a connecting channel located between the inflow channel and outflow channel. In the current study, the effects of the length of the connecting channel and the conductance ratio on the flow characteristics are investigated. Higher velocities are observed in the side layers of the inflow, outflow and connecting channels, forming “M-shaped” velocity profiles. In addition, the velocity recirculations are created in the inner regions of the two right-angle segments just after turning due to the inertial force therein, yielding complicated distributions of the current and electric potential, and found are the diverging and converging of the velocity component parallel to the magnetic field when fluids are turning. The results show that the pressure drop is in close relationship with the conductance ratio and the length of the connecting channel. The characteristics of the fluid velocity, current, electric potential and pressure gradient of LM MHD flows in a u-shaped duct are examined in detail.

Magnetohydrodynamic flows tuning in a conduit with multiple channels under a magnetic field applied perpendicular to the plane of flow

In this study, three-dimensional liquid-metal magnetohydrodynamic flows in a conduit with multiple channels under a uniform magnetic field are numerically investigated. The geometry of the conduit is of a four-parallel-channels system including one inflow channel and three outflow channels. The liquid-metal flows into the inflow channel, then turns through in the transition segment, finally flows into three different outflow channels. This kind of channel system can induce counter flow and co-flow, which is rarely investigated before though the conceptual designs of duct flow in the blanket have suggested this type of flow. A structured grid system is chosen after a series of mesh independence tests in the present study. The axial velocity in the side layer near the first partitioning wall, located between the inflow channel and the first outflow channel, is the highest with the lowest electric potential formed therein. The pressure almost linearly decreases in the main flow direction, except in the transition segment. Moreover, the pressure gradient in the first outflow channel is the largest among the three outflow channels. The interdependency of the current, fluid velocity, pressure, electric potential is examined in order to describe the electromagnetic characteristics of the liquid-metal flows.

Imbalance of the liquid-metal flow and heat extraction in a manifold with sub-channels having locally different eletric conductivity

In this study, the characteristics of liquid metal (LM) magnetohydrodynamic (MHD) flow and convective heat transfer in a manifold with three sub-channels having locally different electric conductivity are investigated with the use of commercial code CFX, allowing an imbalance in flow rate among the sub-channels, which can be used for intensive cooling of the region with higher heat load in the blanket. In a manifold with co-flow multiple sub-channels, the electrical current can cross the fluid regions and channel walls, thus influencing the flow distribution in each sub-channel. In the present study, cases with various arrangements of the electric conductivity in different parts of the channel walls are investigated, yielding different distributions of the current and fluid flow in different cases. Here, the mechanism governing the imbalance in mass flow rate among the sub-channels is discussed. The interdependency of the fluid velocity, current and electric potential of LM MHD flows in the three sub-channels are analyzed in detail. The results show that, in the sub-channel surrounded by the walls with lower electric conductivity, higher axial velocity and superior heat extraction can be obtained, with an effective cooling associated with higher velocity, where the higher velocity is closely related to the distribution of the electromotive component of the current in the flow field.

Numerical analyses on liquid-metal magnetohydrodynamic flow in sudden channel expansion

ABSTRACTThree-dimensional numerical calculations have been performed on the magnetohydrodynamic (MHD) flows through a rectangular channel with sudden expansion, particularly in order to estimate the pressure drop through the sudden expansion. The sudden expansion is in the directions both perpendicular and parallel to the applied magnetic field. The Hartmann number, the Reynolds number and the magnetic Reynolds number are set to ∼100, ∼1000 and ∼0.001, respectively, in simulating laboratory conditions. The continuity equation, the momentum equation and the induction equation were solved numerically by the finite difference method as discretization following the MAC method as solution procedure. On the whole, in the sudden expansion in the direction perpendicular to applied magnetic field, the loss coefficient is estimated to be nearly zero or small. In particular, the loss coefficient becomes negative for small aspect ratios. The reason of negative loss coefficient is attributable to decrease in the induced current just upstream of the expansion. On the other hand, in the sudden expansion in the direction of applied magnetic field, all the cases give positive and large loss coefficients, meaning that the pressure drop through the expansion becomes large. In particular, the loss coefficient becomes considerably large when the Hartmann number increases.

Numerical Study of Flow Motion and Patterns Driven by a Rotating Permanent Helical Magnetic Field

Liquid metal magnetohydrodynamic flow driven by a rotating permanent helical magnetic field in a cylindrical container is numerically studied. A three-dimensional numerical simulation provides insight into the visualization of the physical fields, including the magnetic field, the Lorentz force density, and the flow structures, especially the flow patterns in the meridional plane. Because the screen parameter is sufficiently small, the model is decoupled into electromagnetic and hydrodynamic components. Two flow patterns in the meridional plane, i.e., the global flow and the secondary flow, are discovered and the impact of several system parameters on their transition is investigated. Finally, a verifying model is used for comparison with the previous experiment.

Numerical investigation of the LM MHD flows in a curved duct with an FCI with varying slot locations

This study numerically investigates the liquid-metal (LM) magnetohydrodynamic (MHD) flows in a curved duct with an FCI having three different slot locations and having no slot under a uniform magnetic field perpendicular to the duct. The flow velocity, current density, electric potential, Lorentz force, and pressure in different flow situations are presented in detail. The effects of the location of FCI slot and of the curvature radius on the flow behavior are reviewed. The flow field is examined with an introduction of the electric-field component and electro-motive component of the current, allowing us to analyze the interdependency of the flow variables. The effect of the FCI slot position on the equalization of the pressure in the inner fluid region (inside the FCI) and the gap fluid region (outer the FCI) is examined. The result shows that and the case with an FCI slot located in the neutral position yields the smallest pressure gradient in the main flow direction among the cases with an FCI slot, resulting in the smallest pressure drop. Also, in a flow situation with smaller radius of curvature with the FCI slot in the neutral position, the axial velocity near the inner (in terms of the curvature) part of a cross-section is higher than that near the outer part.

Numerical simulations of a fully developed liquid-metal magnetohydrodynamic flow in a circular duct

In this paper, a kind of new meshless method, two-level radial point interpolation method, has been developed to analyze the fully developed liquid-metal Magnetohydrodynamic (MHD) flow under the externally applied magnetic field in a circular duct with thin conducting walls. This method applied the radial point interpolation method (RPIM) to solve the two levels Galerkin weak form formulations. As the shape functions from RPIM possess Kronecker delta function properties, the essential boundary conditions of MHD flow problems are easily to be enforced. Numerical simulations of MHD flow in the circular duct with partial conducting walls are carried out, showing that the method is very stable in the computation.

ICOPE-15-1063 Numerical analyses on liquid-metal magnetohydrodynamic flow in sudden expansion : Effects of channel aspect ratio and expansion ratio

ICOPE-15-1063 Numerical analyses on liquid-metal magnetohydrodynamic flow in sudden expansion : Effects of channel aspect ratio and expansion ratio

A liquid metal magnetohydrodynamic duct flow with sudden contraction in a direction perpendicular to a magnetic field

This study numerically examines three-dimensional liquid metal (LM) magnetohydrody-namic (MHD) flows in a rectangular, electrically-conducting duct with sudden contraction in a direction perpendicular to a uniform magnetic field. Though diverse analytical, experimental and numerical studies on MHD duct flows are performed, reports dealing with detailed flow characteristics of LM MHD flows in a rectangular duct with sudden contraction in a direction perpendicular to a uniform magnetic field are hardly found. In the present study, with the use of commercial software CFX code, the flow velocity, pressure, Lorentz force, current and electric potential in the MHD duct flow are obtained for flows with two different Hartmann numbers (1000 and 300) with fixed Reynolds number. The interdependency of the flow variables is considered in the discussion of the MHD duct flows with sudden contraction. The results show that large-scaled loops of the current passing through the duct walls and fluid region are created in the LM MHD flow, where the forward-facing wall serves as the path of the returning current that is induced in the fluid region.

Numerical examination of liquid metal magnetohydrodynamic flow in multiple channels in the plane perpendicular to the magnetic field

In the current study, investigated are steady-state, three-dimensional liquid metal (LM) magnetohydrodynamic (MHD) flows in a conduit system including three sub-channels with co-current flows under a uniform magnetic field. Though there have been numerous analytic, experimental and numerical studies on MHD duct flow, detailed flow characteristics of a LMMHD flow in a conduit system with multiple channels have not been reported much. The current study predicts detailed behaviors of the flow velocity, pressure, current and electric potential of LMMHD flows in multiple channels in the plane perpendicular to the magnetic field. Here, the characteristics of the MHD flow in a conduit system with multiple channels are elucidated. The mass flow rate in each of outer channel turns out to be higher than that in the central channel. The mechanism governing the imbalance of mass flow rate in the sub-channels is discussed in detail based on the interdependency of flow variables in LMMHD flow.

Computational Analysis of Magnetohydrodynamic Flows in a Hairpin Duct Under Uniform Magnetic Fields Applied Parallel to the Flow Plane

In this study, three-dimensional liquid-metal magnetohydrodynamic flows in a rectangular hairpin duct with parallel inflow and outflow channels, placed under uniform magnetic fields, are analyzed based on a computational fluid dynamics method. Detailed information on flow velocity, pressure, current, and electric potential in magnetohydrodynamic duct flows is predicted. In the side layers of the inflow and outflow channels, higher velocities are observed, and M-shaped velocity profiles are presented. In the turning segment, the velocity distribution is very complex, yielding complicated induced current therein. The electromagnetic characteristics of the complicated liquid-metal flows are examined in terms of the electromotive and electric-field components of the current. The pressure almost linearly decreases along the main flow direction, except for in the turning segment. Cases with different Hartmann numbers are examined, and the larger the Hartmann number is, the larger the pressure drop is. However, the nondimensional pressure gradient is smaller in cases of larger Hartmann numbers.

Magnetohydrodynamic flow excited by rotating permanent magnets in an orthogonal container

Liquid metal magnetohydrodynamic flow driven by a system of rotating permanent magnets in a container of orthogonal cross-section has been studied. The main objective of the work is to research the impact of magnetic forcing parameters (magnetic field value, magnets arrangement, and angular velocity of their rotation) on the generated hydrodynamic structures and flow modes. On this basis, we contemplate realizing required flow features by setting certain parameters of the driving magnetic system. A numerical study of the problem in the induction-free approximation without taking into account the effect of the variable component of electromagnetic force is presented. The parameters of spin-up modes and steady-state flow regimes have been calculated by three-dimensional direct numerical simulation based on COMSOL Multiphysics 4.3a software and experimentally verified on a specially designed setup using noninvasive Doppler ultrasound technique.