Assessment of Electromagnetic Stirrer Agitated Liquid Metal Flows by Dynamic Neutron Radiography (original) (raw)
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Dynamic Neutron Radiography for Liquid Metal Applications
Le Centre pour la Communication Scientifique Directe - HAL - Archive ouverte HAL, 2015
Due to the non-transparency of metals it is nearly impossible to observe how inclusions behave within a liquid metal. At the same time numerical models, which generally are powerful tools for design of different types of metallurgical and other equipment associated with liquid metal, usually contain a high number of degrees of freedom due to the complexity of turbulent flows. Therefore, experimental verification of the numerical models is an essential task, which was hitherto not satisfactorily solved by established technologies. This contribution presents a recent and breakthrough experimental method, which makes liquid metal transparent: dynamic neutron radiography. It allows to visualize dynamics of solid inclusions in liquid metal flows within a scaled-down equipment, keeping fixed non-dimensional hydrodynamic and electromagnetic parameters and applying a permanent magnets technology for electromagnetic agitation in the setup. Such method allows to step forward in understanding two-phase liquid metal flows as well as ensure innovative experiments for improvements in metallurgical equipment, bubbly liquid metal columns, preparation of metal matrix nanocomposites and others.
Applied Radiation and Isotopes, 2004
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 twophase 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. r
Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 2011
The European Isotope Separation On-Line (EURISOL) design study completed in 2009 examined means of producing exotic nuclei for fundamental research. One of the critical components identified in the study was a high-power neutron spallation source in which a target material is impacted by a proton beam producing neutrons by a process known as spallation. Due to the high heat power deposition, liquid metal, in this case mercury, is the only viable choice as target material.
Nuclear Instruments & Methods in Physics Research Section A-accelerators Spectrometers Detectors and Associated Equipment, 1994
Experiments on visualization of fluid phenomena in a metallic vessel were conducted using a high-speed video camera with a steady thermal neutron beam . The Japan Research Reactor 3M, whose flux at the imaging plate is 1.5 X 10 8 n/cm 2 s, of Japan Atomic Energy Research Institute was used as a neutron source . The imaging system for high frame-rate neutron radiography with the steady thermal neutron beam consisted of a high sensitivity scintillator, 6LiF/ZnS :Ag, an image intensifier whose gain was a factor of 100 000 at the maximum, and a high-speed video which could record phenomena at 1000 frames/s for 14 min by using an ordinary VHS tape with the recording time of 120 min at the normal speed. Visualization of air-water two-phase flows in a rectangular duct with 2.4 mm gap and 40 mm width were successfully performed with the steady thermal neutron beam and this imaging system at frame rates up to 1000 frames/s. The shapes and the behavior of bubbles and liquid films were clearly observed . The rising velocities of slug bubbles and the flow regimes could be also measured . It was clarified that this new technique may have significant advantages both in visualizing and measuring high-speed phenomena when the visible light is not applicable . 0168-9002/94/$07 .00
Applications for real-time neutron radiography for convection driven flow pattern transition studies
IEEE Transactions on Nuclear Science, 2005
Thermal hydraulics design of nuclear reactors require extensive studies on two-phase flow pattern. In particular, for reactors using convection driven flow, such as advanced heavy water reactor being designed by the Bhabha Atomic Research Centre (BARC), Bombay, India, very little data exists on flow pattern behavior. Also such reactors using natural circulation face the problem of flow pattern instabilities due to various reasons and no data exists for such instabilities. We have used real-time neutron radiography methods in order to study flow pattern instability and develop thermal hydraulics model for such a reactor. A real time neutron imaging system has been developed for the visualization and measurement of void fraction inside metallic pipes. The system has been installed at the APSARA Reactor, BARC, Bombay, India. Experiments have been conducted on subsystems (SS) test sections of different diameters at pressure ranging from 1 to 40 bar and at various power levels. We report in this paper on the method and components used for this imaging system and some preliminary results of these experiments on void fraction measurement using this system. Index Terms-Intensified charge-coupled device (ICCD), radiography, real time, two-phase flow.
Measuring liquid film thickness in annular two-phase flows by cold neutron imaging
Experiments in Fluids, 2013
An overview of a measurement method for liquid film thickness in annular flows based on cold neutron imaging is given here. Neutron imaging being a nonintrusive, contactless method is attractive option for twophase flow investigations offering an excellent contrast. It can provide with information at a high spatial resolution on the flow structure, like the thickness of the liquid film in annular flows. The method has been optimized, and its performance, regarding bias, statistical accuracy, upper and lower detection limits, has been thoroughly quantified using computational tools and measurement results. The technique has been developed based on nuclear fuel bundle models; however, it is applicable practically to annular flows in any arbitrary flow channel geometry of interest.
High-frame rate, fast neutron imaging of two-phase flow in a thin rectangular channel
We have demonstrated the feasibility of performing high-frame-rate, fast neutron radiography of air–water two-phase flows in a thin channel with rectangular cross section. The experiments have been carried out at the accelerator facility of the Physikalisch-Technische Bundesanstalt. A polychromatic, high-intensity fast neutron beam with average energy of 6 MeV was produced by 11.5 MeV deuterons hitting a thick Be target. Image sequences down to 10 ms exposure times were obtained using a fast-neutron imaging detector developed in the context of fast-neutron resonance imaging. Different two-phase flow regimes such as bubbly slug and churn flows have been examined. Two phase flow parameters like the volumetric gas fraction, bubble size and mean bubble velocities have been measured. The first results are promising, improvements for future experiments are also discussed.
Single-magnet rotary flowmeter for liquid metals
Journal of Applied Physics, 2011
We present a theory of single-magnet flowmeter for liquid metals and compare it with experimental results. The flowmeter consists of a freely rotating permanent magnet, which is magnetized perpendicularly to the axle it is mounted on. When such a magnet is placed close to a tube carrying liquid metal flow, it rotates so that the driving torque due to the eddy currents induced by the flow is balanced by the braking torque induced by the rotation itself. The equilibrium rotation rate, which varies directly with the flow velocity and inversely with the distance between the magnet and the layer, is affected neither by the electrical conductivity of the metal nor by the magnet strength. We obtain simple analytical solutions for the force and torque on slowly moving and rotating magnets due to eddy currents in a layer of infinite horizontal extent. The predicted equilibrium rotation rates qualitatively agree with the magnet rotation rate measured on a liquid sodium flow in stainless steel duct.
Flow visualization of segregation process in a fluidized-bed by neutron radiography
IEEE Transactions on Nuclear Science, 2005
Owing to a wide variety in fluidization properties of particles, segregation phenomena are hardly avoided in industrial fluidized-bed facilities. For the stability and controllability in operation of such fluidised-beds, understanding of the relevant mechanism of particulate segregation is indispensable. This paper describes an experimental observation of the particulate segregation in a binary mixture system visualized successfully by using a neutron radiography (NR). The NR gives real time information of the segregation process, and this information will be very useful in understanding the segregation mechanism.