Liquid Metal Two-phase Flow Research Articles

Large-Scale Test Facility for Modeling Bubble Behavior and Liquid Metal Two-Phase Flows in a Steel Ladle

Abstract A new experimental facility has been designed and constructed which represents a 1:5.25 model of an industrial 185 t steel ladle. This setup is intended for systematic investigations of complex liquid metal multiphase flows created by gas blowing from the bottom. Two tons of a Sn-40 wt pct Bi alloy are employed as working fluid, its thermophysical properties are very similar to those of liquid steel. The relatively low operating temperatures (T ~ 200 °C) compared to the real industrial process allow the use of powerful measuring techniques for characterizing the behavior of the gas phase and resulting flow regimes. Argon gas is injected through diverse plug systems into a cylindrical fluid vessel which is equipped with a pressure tight lid to achieve low-pressure conditions for vacuum processing. This paper presents first measurements of the gas distribution close to the free liquid metal surface for various gas flow rates, plug positions and types. Moreover, the pressure in the vessel has been varied between 1 mbar and ambient pressure. The experiments provide a copious data base about flow regimes, void fraction, liquid and bubble velocities, and bubble properties, which can be used to provide so far unknown boundary conditions for numerical simulations of various metallurgical reactors such as steelmaking converters or steelmaking ladles.

Electromagnetic interaction between a rising spherical particle in a conducting liquid and a localized magnetic field

Lorentz force velocimetry (LFV) is a non-contact electromagnetic flow measurement technique for electrically conductive liquids. It is based on measuring the flow-induced force acting on an external permanent magnet. Motivated by extending LFV to liquid metal two-phase flow measurement, in a first test we consider the free rising of a non-conductive spherical particle in a thin tube of liquid metal (GaInSn) initially at rest. Here the measured force is due to the displacement flow induced by the rising particle. In this paper, numerical results are presented for three different analytical solutions of flows around a moving sphere under a localized magnetic field. This simplification is made since the hydrodynamic flow is difficult to measure or to compute. The Lorentz forces are compared to experiments. The aim of the present work is to check if our simple numerical model can provide Lorentz forces comparable to the experiments. The results show that the peak values of the Lorentz force from the analytical velocity fields provide us an upper limit to the measurement results. In the case of viscous flow around a moving sphere we recover the typical time-scale of Lorentz force signals.

Assessment of Electromagnetic Stirrer Agitated Liquid Metal Flows by Dynamic Neutron Radiography

This paper presents qualitative and quantitative characterization of two-phase liquid metal flows agitated by the stirrer on rotating permanent magnets. The stirrer was designed to fulfill various eddy flows, which may have different rates of solid particle entrapment from the liquid surface and their homogenization. The flow was characterized by visualization of the tailored tracer particles by means of dynamic neutron radiography, an experimental method well suited for liquid metal flows due to low opacity of some metals for neutrons. The rather high temporal resolution of the image acquisition (32 Hz image acquisition rate) allows for the quantitative investigation of the flows up to 30 cm/s using neutron particle image velocimetry. In situ visualization of the two-phase liquid metal flow is also demonstrated.

Non-contact electromagnetic flow measurement in liquid metal two-phase flow using Lorentz force velocimetry

Non-contact electromagnetic flow measurement in liquid metal two-phase flow using Lorentz force velocimetry

Electromagnetic interaction between a permanent magnet and laminar flow of a moving sphere in a conducting liquid

Lorentz force velocimetry (LFV) is a non-contact electromagnetic flow measurement technique for electrically conducting liquids. It is based on measuring the flow-induced force acting on an externally arranged permanent magnet. Motivated by extending LFV to liquid metal two-phase flow measurement, in a previous test we considered the free rising of non-conductive bubbles/particles in a thin tube of liquid metal (GaInSn) initially at rest. We observed that the Lorentz force signals strongly depend on the size of the bubble/particle and on the position, where it is released. Moreover, the force signals cannot be reproduced in detail, which necessitates a statistical analysis. This is caused by chaotic trajectories due to the rising velocities of about 200 mm/s. Therefore, in this paper, we use an improved setup for controlled particle motions in liquid metal. In this experiment, the particle is attached to a straight fishing line, which suppresses any lateral motion, and is pulled by a linear driver at a controllable velocity (0-200 mm/s). For comparison, we solve the induction problem numerically using Oseen's analytical solution of the flow around a translating sphere that is valid for small but finite Reynolds numbers. This simplification is made since the precise hydrodynamic flow is difficult to measure or to compute. The aim of the present work is to check if our simple numerical model can provide Lorentz forces comparable to the experiments. Although Oseen's solution becomes inaccurate near the sphere for finite Reynolds numbers, it provides a fore-aft asymmetry of the flow and is globally well-behaved. It provides an upper limit to the measurement results. We recover the peak-delay of the Lorentz force signals as well.

Magnetic flux distortion in two-phase liquid metal flow: Model experiment

In this paper, we present the model experiments in order to study the magnetic flux distortion of a two-phase liquid metal flow excited by an AC magnetic field in a range of pulsation where Faraday induction and Lorentz force effects are significant. These experiments realized with solid aluminum rods allow to characterize the effects of flow velocity (0 ≲ U≤1 ms−1), void fraction (0≤α≤6.9 %), pulsation of the AC magnetic field (1.5×103≤ω≤12.5×103 rad s−1), and of two different void geometries. The results are analyzed on the basis of a first order expansion of magnetic flux in U and α. Despite the strong coupling between Faraday induction and Lorentz force effects, the results show that the contributions of U and α on a magnetic flux distortion can be well separated at both low magnetic Reynolds number and α values. These results are independent of void geometry.

Note: Void effects on eddy current distortion in two-phase liquid metal.

A model based on the first order perturbation expansion of magnetic flux in a two-phase liquid metal flow has been developed for low magnetic Reynolds number Rem. This model takes into account the distortion of the induced eddy currents due to the presence of void in the conducting medium. Specific experiments with an eddy current flow meter have been realized for two periodic void distributions. The results have shown, in agreement with the model, that the effects of velocity and void on the emf modulation are decoupled. The magnitude of the void fraction and the void spatial frequency can be determined from the spectral density of the demodulated emf.

Experimental investigation of sodium boiling heat exchange in fuel subassembly mockup for perspective fast reactor safety substantiation

Numerical modeling of ULOF-type accident development in sodium-cooled fast reactor carried out using the COREMELT code indicate the development and spreading of sodium boiling in the core accompanied with fluctuations of reactor technological parameters lasting over a period of several tens of a seconds. Significant influence on the calculation results is produced by two-phase coolant flow regime so the code boiling models requiring experimental confirmation. Design solution that includes the “sodium cavity” above the reactor core was suggested in order to exclude reactor accidents resulting in the destruction of reactor core elements. As the result of experimental studies on heat exchange during sodium boiling in the fast reactor fuel subassembly mockup with “sodium cavity” conducted on the AR-1 test facility under natural circulation conditions it was demonstrated possibility of long-term fuel pins simulators stable cooling. Schematic map of two-phase liquid metal flow regimes in fuel pin bundles is presented, data on the heat transfer during liquid metal coolant boiling in the fuel assembly are presented and analyzed. The obtained experimental data are used for further elaboration of the calculation model of sodium boiling in the fuel assembly and for COREMELT computer code verification.

Visualization of Liquid Metal Two-phase Flows in a Physical Model of the Continuous Casting Process of Steel

We present an experimental study concerned with investigations of the two-phase flow in a mock-up of the continuous casting process of steel. A specific experimental facility was designed and constructed at HZDR for visualizing liquid metal two-phase flows in the mold and the submerged entry nozzle (SEN) by means of X-ray radioscopy. This setup operates with the low melting, eutectic alloy GaInSn as model liquid. The argon gas is injected through the tip of the stopper rod into the liquid metal flow. The system operates continuously under isothermal conditions. First results will be presented here revealing complex flow structures in the SEN widely differing from a homogeneously dispersed bubbly flow. The patterns are mainly dominated by large bubbles and large-area detachments of the liquid metal flow from the inner nozzle wall. Various flow regimes can be distinguished depending on the ratio between the liquid and the gas flow rate. Smaller gas bubbles are produced by strong shear flows near the nozzle ports. The small bubbles are entrained by the submerged jet and mainly entrapped by the lower circulation roll in the mold. Larger bubbles develop by coalescence and ascend toward the free surface.

Development of a fast neutron imaging system for investigating two-phase flows in nuclear thermal–hydraulic phenomena: A status report

The present paper gives an overview of the status of an ongoing project aiming at the development of a fast neutron imaging system for investigating two-phase flows primarily in the context of nuclear fuel bundle development. Other potential subjects for investigations include steam explosions for severe accident research and liquid metal two-phase flows for Gen IV reactor systems. The project is carried out in the form of a feasibility study that should enable estimation of the ultimate imaging capabilities achievable. The imaging system used in the feasibility study consists of a compact, deuterium–deuterium fusion based neutron generator and dedicated imaging detectors. For the latter two promising concepts are developed in parallel: one is based on an array of plastic scintillators coupled with silicon photomultipliers, the other on a special multi-foil recoil proton converter coupled to a position sensitive charge readout using a micro pattern gas detector.

Measurements of Turbulence in a Liquid-Metal Two-Phase Flow by Using a Miniature Electro-Magnetic Probe

A nitrogen gas-lead bismuth two-phase flow was experimentally studied as a two-phase flow with large liquid-to-gas density ratio. Experiments were performed to understand turbulent structure in a liquid-metal two-phase flow by using a miniature electro-magnetic probe. Radial profiles of axial liquid velocity and turbulence intensity were measured by using the electro-magnetic probe. Turbulence is induced mainly by rising bubbles in the liquid-metal. Measurement results show that the turbulence intensity at the tube center was proportional to the void fraction to the power of 0.8 for higher void fraction at the present experimental conditions.

Application of X-ray radioscopic methods for characterization of two-phase phenomena and solidification processes in metallic melts

X-ray attenuation techniques are an important diagnostic tool for investigating liquid metal two-phase flows or solidification studies in metallic alloys. X-ray visualization enables a general, intuitive understanding of flow phenomena or pattern formation in opaque liquid metal systems. Real-time and in-situ observations of the density distribution within thin solidifying samples achieve a spatial resolution of a few microns and contribute significantly to an improved understanding of dendritic growth processes. Moreover, X-ray radioscopy is a useful tool for a non-invasive, in-situ visualization and characterization of gas bubbles in nontransparent melts or for observations of the formation of metal foams. In this paper we consider three different fields of application which are under intensive investigation at HZDR and TUD: the bottom-up solidification of Ga-In alloys under the influence of buoyancy-driven and electromagnetically driven convection, the injection of Ar gas into liquid GaInSn, the study of Al foams with respect to foam formation and the characterization of their internal structure.

BUBBLE MEASUREMENTS IN LIQUID-METAL TWO-PHASE FLOW BY USING A FOUR-SENSOR PROBE

BUBBLE MEASUREMENTS IN LIQUID-METAL TWO-PHASE FLOW BY USING A FOUR-SENSOR PROBE

F133 液体金属気液二相流のボイド率分布計測(OS-11:沸騰・二相流(4))

F133 液体金属気液二相流のボイド率分布計測(OS-11:沸騰・二相流(4))

Coupling the VOF and the MHD models for the simulation of bubble rising in a metallic liquid

In the last few decades magnetohy-drodynamic (MHD) effects have attracted growing interest because of its potential impact on numerous industrial technologies such as metallurgy, crystal growth, electron or laser beam melting/evaporation of surfaces, etc… An example of such flow is the Bubble driven flows which have found wide applications in industrial technologies. In metallurgical processes gas bubbles are injected into a bulk liquid metal to drive the liquid into motion, to homogenise the physical and chemical properties of the melt or to refine the melt. For such gas–liquid metal two-phase flows, external magnetic fields provide a possibility to control the bubble motion in a contactless way. Our interest is devoted to the motion of gas bubbles in liquid metals under the influence of a magnetic field. The numerical scheme used in this paper is based on the volume of fluid (VOF) method interFoam of the OpenFoam code, which uses an interface tracking algorithm for the simulation of the two-phase flow coupled with an incompressible laminar magneto-hydrodynamics model mhdFoam of same code. The solver is at its earlier stage and in this paper; we consider the case of a single, isolated bubble rising in a tube of stagnant liquid metal exposed to a longitudinal magnetic field.

Application of high frame-rate neutron radiography to liquid-metal two-phase flow research

Liquid metal two-phase flows in metallic vessels were studied by using high frame-rate neutron radiography. Both a bubble column and a gas-lift loop arrangement have been considered. Liquid velocity field of two-phase flow in a flat bubble column with rectangular cross-section was measured precisely by the particle tracking velocimetry. In a gas-lift loop, simultaneous measurements of void fraction by using high frame-rate neutron radiography and four-sensor probe were also performed to observe the bubble-probe interaction. Asymmetric Abel inversion was applied to compare the radial void fraction profiles. Measured radial void fraction profiles obtained by neutron radiography and electrical conductivity probe agreed well with each other. From these measurements, the measurement error and basic characteristics of gas–liquid metal two-phase flow were clarified.

Measurements of liquid–metal two-phase flow by using neutron radiography and electrical conductivity probe

Neutron radiography and electrical four-sensor conductivity probe method were applied to measurement of liquid–metal two-phase flow. Visualization and measurements of nitrogen gas–molten lead bismuth two-phase flow were performed by using neutron radiography technique. Simultaneous measurements of void fraction by using high-frame-rate neutron radiography and four-sensor probe were also performed to observe the bubble–probe interaction. At the same experimental conditions, four-sensor probe was applied to the measurements of interfacial area concentration in radial direction. From the visualization of the two-phase flow, it turned out that cap bubbles or elongated slug bubbles were dominant at the superficial gas velocity of 1.1–38.3 cm/s and no stable Taylor bubbles were detected in this experiment. Measured radial void fraction profiles obtained by neutron radiography and electrical conductivity probe agreed well with each other. From these measurements, the measurement error and basic characteristics of gas–liquid–metal two-phase flow were clarified.

Velocity field measurement in gas–liquid metal two-phase flow with use of PIV and neutron radiography techniques

To establish reasonable safety concepts for the realization of commercial liquid-metal fast breeder reactors, it is indispensable to demonstrate that the release of excessive energy due to re-criticality of molten core could be prevented even if a severe core damage accident took place. Two-phase flow due to the boiling of fuel-steel mixture in the molten core pool has a larger liquid-to-gas density ratio and higher surface tension in comparison with those of ordinary two-phase flows such as air–water flow. In this study, to investigate the effect of the recirculation flow on the bubble behavior, visualization and measurement of nitrogen gas-molten lead bismuth in a rectangular tank was performed by using neutron radiography and particle image velocimetry techniques. Measured flow parameters include flow regime, two-dimensional void distribution, and liquid velocity field in the tank. The present technique is applicable to the measurement of velocity fields and void fraction, and the basic characteristics of gas–liquid metal two-phase mixture were clarified.

The Performance of Electromagnetic Flowmeters in a Liquid Metal Two-Phase Flow

In order to investigate the characteristics of an electromagnetic flowmeter in a liquid metal two-phase flow, AC electromagnetic flowmeters were designed and manufactured. Two-phase flow experiments, encompassing bubbly to slug flow regimes, were realized with a water-air mixture and a liquid sodium-nitrogen mixture, respectively. The relation ΔU TP =ΔU SP /(1—α), between the flow induced electromotive force (e.m.f.) of a single-phase flow and that of a two-phase flow, was verified by the measured e.m.f.s and the void fraction α for a bubbly flow regime. Whereas there is no difference in the shape of the flow induced e.m.f. between single-phase and bubbly flow, the signal amplitude of the bubbly flow is greater than that of the single-phase flow under the same water or liquid sodium flow rate, since the real liquid velocity is higher than that of the single-phase flow. In the case of a slug flow, the phase and the amplitude of the flowmeter output changed drastically when a slug bubble passed through the flowmeter. Therefore, the electromagnetic flowmeter shows good potential as a useful device for identifying the flow regimes. The void fraction in a bubbly flow can be measured using two electromagnetic flowmeters.

An experimental study on the characteristics of electromagnetic flowmeters in the liquid metal two-phase flow

Based on the previous study for the water-air mixture, the characteristics of AC electromagnetic flowmeter were investigated in the liquid metal two-phase flow. Two-phase flow experiments, encompassing bubbly to slug flow regimes, were conducted with the liquid sodium–nitrogen mixture. The simple relation Δ U TP=Δ U SP(1− α) , relating flowmeter signal between single-phase flow and two-phase flow, was verified with measurements of the potential differences and the void fraction α for a bubbly flow regime in water-air loop. Whereas there was no difference in the shape of the raw signal between single-phase flow and bubbly flow, the signal amplitude of bubbly flow was greater than that of single-phase flow under the same liquid flow (sodium or water) rates, since the passage area of the liquid flow was reduced. In the case of slug flow, the phase and the amplitude of the flowmeter output showed a change in the flow characteristics around each slug bubble and the position of a slug bubble itself. Therefore, the electromagnetic flowmeter shows a good potential as a useful device for identifying the flow regimes. The void fraction can be simply measured with two electromagnetic flowmeters for a low-void fraction flow such as bubbly flow. Thus, the flowmeters can be used to measure the void fraction for a liquid sodium.