Liquid Metal Magnetohydrodynamic Research Articles

Physical Background, Computations and Practical Issues of the Magnetohydrodynamic Pressure Drop in a Fusion Liquid Metal Blanket

In blankets of a fusion power reactor, liquid metal (LM) breeders, such as pure lithium or lead-lithium alloy, circulate in complex shape blanket conduits for power conversion and tritium breeding in the presence of a strong plasma-confining magnetic field. The interaction of the magnetic field with induced electric currents in the breeder results in various magnetohydrodynamic (MHD) effects on the flow. Of them, high MHD pressure losses in the LM breeder flows is one of the most important feasibility issues. To design new feasible LM breeding blankets or to improve the existing blanket concepts and designs, one needs to identify and characterize sources of high MHD pressure drop, to understand the underlying physics of MHD flows and to eventually define ways of mitigating high MHD pressure drop in the entire blanket and its sub-components. This article is a comprehensive review of earlier and recent studies of MHD pressure drop in LM blankets with a special focus on: (1) physics of LM MHD flows in typical blanket configurations, (2) development and testing of computational tools for LM MHD flows, (3) practical aspects associated with pumping of a conducting liquid breeder through a strong magnetic field, and (4) approaches to mitigation of the MHD pressure drop in a LM blanket.

Numerical simulation of liquid metal MHD flows in a conducting rectangular duct with triangular strips

Magnetohydrodynamic (MHD) pressure drop remains a key issue in the application of liquid metal blankets in nuclear fusion reactors. MHD pressure drops and velocity distributions in MHD duct flows are closely related to the shape of the duct cross-section. In this paper, MHD flows in an ordinary electrically conducting rectangular duct (R-duct), and an electrically conducting rectangular duct with triangular strips (RTS-duct) subjected to a uniform magnetic field are investigated numerically using an in-house MHD solver developed in OpenFOAM. The results show that the velocity fluctuation of the MHD flow in the RTS-duct grows, and the dimensionless MHD pressure drop reduces as the direction of the magnetic field is fixed, and the Hartmann number increases. The velocity fluctuation in the RTS-duct spreads more easily when the triangular strips (TS) are on the Hartmann walls instead of the side walls as the magnetic field intensity is the same. Besides, the MHD pressure drop in the RTS-duct is only a little bit higher than that in the R-duct as the TSs are on the Hartmann walls. The MHD pressure drop in the RTS-duct is over 20 % higher than that in the R-duct, and the relative difference increases with the Hartmann number increasing when the TSs are on the side walls. The results about the MHD pressure drop and the flow instability in the RTS-duct can be referenced in the liquid metal blanket design.

Numerical Research on the Flow Fields in the Power Generation Channel of a Liquid Metal Magnetohydrodynamic System.

The flow fields in the power generation channel of a magnetohydrodynamic system, which uses a mixture of liquid metal as the power generation medium and a low-boiling-point working medium as the carrying medium, were numerically investigated in the present paper. The influences of the magnetic field intensity, void fraction, and bubble diameter were examined, respectively. The results indicate that an increase in the magnetic field intensity will enhance the turbulence intensity and may reduce the stability of the flow fields, whereas increasing the void fraction will contribute to better flow stability in the power generation channel. The effect of the bubble diameter on the flow field stability is negligible in the range of the study. In addition, it is found that the volume fraction of the gas phase exhibits an M-shape distribution by studying the variation of the slip velocity over time. This paper presents our latest findings and will provide a fundamental theory for future design and operation of liquid metal magnetohydrodynamic systems.

Numerical investigation on the comparison of the MHD flow features of lithium and eutectic lead-lithium alloy in a conduit with four-parallel ducts

• The difference in the MHD (magnetohydrodynamics) flow characteristics between Lithium (Li) and eutectic lead-lithium (LiPb) is analyzed. • Commercial software CFX is used to investigate the LM MHD flows in a conduit with four-parallel ducts. • The effect of the local electric conductivity of the duct walls on the mass imbalance among the outlet ducts is investigated. • The mechanism governing the flow imbalance in the four-parallel ducts is discussed. • The pressure drop and mass flow rate in the case with Pb-17Li is larger than those in the case with pure Li. At present, the magnetohydrodynamic (MHD) flows of liquid-metal (LM) Pb-17Li and pure Li through a conduit with four-parallel ducts having partly different electrical conductivity are numerically analyzed. Here, the conduit system can cause counter flow and co-flow, which can be a good candidate for the design of duct flow in the liquid-metal blanket. Meanwhile, since lithium (Li) and eutectic lead-lithium (LiPb) are the promising liquid metal materials for a self-cooled blanket, the MHD flow characteristics of these two liquid metals become important and have to be taken into account during the design of a fusion liquid-metal blanket. The current study focuses on the electromagnetic features of the two liquid-metal flows, and considers the flow imbalance that is affected by different wall electrical conductivity in four-parallel ducts. The results present that the pressure drop and mass flow rate in the case with Pb-17Li is larger than those in the case with pure Li because of different properties of the liquid metals used therein. Furthermore, the influence of the local electrical conductivity of the structural walls on the flow imbalance among the outlet ducts is analyzed for the two different working fluids, and the mechanism governing the flow imbalance in the outlet ducts is discussed.

Liquid metal free surface dynamics in rotating permanent magnet stirrer

We study liquid metal stirring by rotating permanent magnets in a laboratory-scale rectangular glass container. The main goal is numerical model validation using experimental free surface shape data. We find reasonable agreement between the experiments and coupled liquid metal magnetohydrodynamics simulations. Since the surface tension forces are not dominant here, free surface is deformed mainly by the dynamic pressure of the bulk flow. Therefore, we can conclude that not only the free surface profile is similar to experiments, but the bulk flow must be also very similar.

Effect of static liquid Galinstan on common metals and non-metals at temperatures up to 200 °C

Liquid metal Galinstan (GaInSn) is corrosive in nature against other solid metals as its base component is gallium. This study experimentally investigated the compatibility of GaInSn with eight common metals at temperatures up to 200 °C for 2000 h, including aluminum, copper, brass, ferritic and austenitic stainless steels (E-brite, SS304L, SS316L), and nickel-chromium alloys (Inconel and Hastelloy). This assessment aims to assist in design and material selection of a liquid metal magnetohydrodynamics system that houses Galinstan for power generation by low temperature natural heat sources or industrial waste heat. Design and fabrication of this renewable power system required assurance of material compatibility with common construction and instrumentation materials. The most severe corrosion effects of GaInSn on the metal alloys were observed on aluminum, copper, and brass, which confirms the results of previously conducted studies. No obvious corrosion on stainless steel or nickel–chromium alloys were observed by this study, which reveals that stainless steel has a good resistance to attack by GaInSn up to 200 °C. Six non-metals were also evaluated, including acronitrile butadiene styrene (ABS), acrylic, nitrile rubber (Buna N), nylon, polyvinyl chloride (PVC), and Teflon, which were deemed to be compatible with GaInSn up to the temperatures tested.

Liquid metal MHD effect and heat transfer research in a rectangular duct with micro-channels under a magnetic field

The liquid metal blanket of a fusion reactor acts the role of tritium multiplication and energy transportation in a strong magnetic field environment. Liquid metal in fusion blanket is different from traditional flow and heat transfer due to magneto hydrodynamics (MHD) effects. A numerical simulation is employed to investigate the convection heat transfer between liquid metal and micro-channels heated surface under an external magnetic field. It can be found that under the influence of magnetic field, liquid metal can produce strong jet near the wall which drives the liquid metal flow together inside the channel. The MHD Hunt flow effect is intensified with the enhancement of the magnetic field and the results indicate that the magnetic field is beneficial to the energy transport and conversion of liquid metal blanket due to the jet flow on the wall that caused by the magnetic field. From the point of view of enhanced heat transfer, 32% of the heat transfer enhancement under the influence of strong magnetic field provides a new way to solve the heat transfer with high heat flux density. The expression is fitted between Nu number with Re number, the magnetic interaction number and flow distance, which can be used to predict the change of heat transfer intensity between the liquid metal and the micro-channels heated plate with the magnetic field intensity.

Experimental investigation of liquid metal MHD flow entering a flow channel insert

Insulating flow channel inserts (FCI) in ducts of liquid metal blankets decouple electrically the fluid domain from the conducting thick-walled structure. They interrupt current paths across well-conducting walls and thereby reduce significantly magnetohydrodynamic (MHD) pressure drop. Pipe flow of an electrically conducting liquid metal entering a region where walls are covered by a FCI is investigated experimentally under the influence of a strong uniform magnetic field. The abrupt change in wall conductivity leads to 3D MHD effects that are studied by measuring pressure and electric potential distribution along the duct wall. It is shown that FCIs may reduce pressure drop by at least one order of magnitude but 3D effects at the entrance of FCIs may reduce the efficiency of the insulating inserts by some degree.

Numerical Characterization of a Liquid Metal Magnetohydrodynamic Alternate Generator in the Laminar-Regime under Inductionless Approximation

Numerical Characterization of a Liquid Metal Magnetohydrodynamic Alternate Generator in the Laminar-Regime under Inductionless Approximation

Numerical modelling of liquid metal magnetohydrodynamic flow in an electrically and thermally coupled annulus under reduced gravity

For a high-precision spaceborne magnetohydrodynamic (MHD) sensor, temperature drift is troublesome for engineers. The thermal properties of liquid metal MHD (LMMHD) flow in the sensor should be considered. The thermo-fluid behaviour of LMMHD flows and its effect on the output characteristic of the sensor were numerically investigated to explore the underlying mechanism. Based on the Boussinesq approximation, a three-dimensional model of the MHD effect in an electrically and thermally coupled annulus was simplified and implemented in a finite-element framework. The visual patterns of the velocity and electric potential depended on the type of temperature boundary, the magnitude and direction of the applied force, and the angular rate of the inlet and outlet. When the magnitude of the applied force increased from microgravity to gravity, the fluid gradually transformed from a viscous flow to a convective flow. The competitive action between the magneto- and natural convection had a substantial influence on the distribution of the electric potential, as the applied force was perpendicular to the magnetic field. The result will provide a reference for space applications and ground tests of MHD sensors.

3D multiphysics simulation and analysis of a low temperature liquid metal magnetohydrodynamic power generator prototype

Magnetohydrodynamic (MHD) power generation is an interdisciplinary process, which was studied heavily in the late 1960′s but interest soon subsided. However, the current socio-economic climate demands more diversity in renewable energy sources. MHD generators using liquid metal as the working fluid represent a viable option for this augmentation. Furthermore, the steady increase in accessible computational capabilities provides a powerful new tool for interdisciplinary modeling and multiphysics simulations. These factors suggest that this is an opportune time to reevaluate MHD power generation. This paper provides mathematical background as well as a detailed multiphysics model of a low temperature liquid metal MHD power generator built in COMSOL. Simulation details are provided in addition to a comparison to experimental results. The prototype studied in this paper is the first proof of concept of a permanent magnet excited liquid metal MHD generator using Gallium as its working fluid.

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.

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.

Design and Simulation of the Channel Model of a LMMHD Generator Based on Halbach

To improve the efficiency of the liquid metal magnetohydrodynamic (LMMHD) generator, a new type of magnet structure of LMMHD system is designed in paper. The internal magnetic gathering capability is enhanced by imitating the arrangement of the Halbach array magnet. The magnetic induction intensity of conventional magnetic channel, Halbach magnet channel, and the new type of magnet channel, which is derived from basic Halbach are compared via ANSYS Maxwell 2D model. Simulation results show that Halbach magnets have better capacity of magnetism gathering and are more efficient at gathering electricity than conventional methods. The new type of magnetic has advantages of small size, low cost, high induction intensity, high output voltage and high power.

Performance Analysis of Heaving Float Wave Energy Converter with Liquid Metal MHD Generator

Heaving float wave energy converter/conversion (WEC), which makes use of liquid metal magnetohydrodynamics (LMMHD) generator, converts directly the linear motion of heaving float into electrical power. In this paper, effect of magnetic flux density on performance of heaving float LMMHD-WEC is analytically investigated. The results reveal that the capture width ratio, the load voltage, the output power, the system efficiency have maximum values with the increase of magnetic flux density.

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.

Thermal mixing enhancement of liquid metal MHD free-surface flow by optimizing vortex generator arrays

Liquid divertor concepts in fusion reactor research have been widely studied. Recently, thermal mixing enhancement of the locally heated free-surface of liquid metal MHD (Magneto-Hydro-Dynamics) film flow using one vortex generator was proposed and investigated by the authors. In this study, an inline arrangement of many hemispherical protrusions to generate many vortices in their wakes was proposed, and the transport characteristics of high temperature fluid at the free-surface to the bottom (i.e., thermal mixing) in liquid metal MHD film flow was investigated experimentally. The experiments for three streamwise pitch lengths between the protrusions under various transverse magnetic field strengths (B = 0.00–0.33T) for two flowrate conditions were conducted. As the results, the heat flux distributions on the bottom wall of the film flow and the efficiency of heat transport showed the existence of the optimum streamwise pitch length for the thermal mixing enhancement even under relatively high transverse magnetic field. Therefore, the inline arrangement of many hemispherical protrusions can be considered as one of the candidates for thermal mixing enhancement methods of liquid metal MHD free-surface flow application.

Numerical Study of the Gas-Liquid Two-Phase Flow in a Self-Designed Mixer for a Ga-R113 MHD System

Liquid metal MHD (Magneto-Hydro-Dynamic) systems can be employed to produce electricity from a wide range of heat resources. In such a system, a low-boiling organic fluid and a high-temperature liquid metal fluid mix. The former evaporates, and carries the latter to flow through an MHD channel, where the electricity is generated. The mixing process and the gas-liquid flow characteristics will have a significant effect on the power generating efficiency. In the present work, trifluorotrichloroethane (R113) was chosen as the organic fluid, and gallium (Ga) as the liquid metal, respectively. Numerical study was subsequently carried out on the gas-liquid flow and heat transfer in a self-designed spherical mixer. The effects of the main factors, including the inlet velocities and inlet temperatures of Ga and R113, were separately determined, with suggested values or ranges discussed in detail.

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.