Liquid Metal Jet Research Articles

Production of Palladium-103 (103Pd) from a thin rhodium foil target – Improved cooling concept

Palladium-103 (103Pd) is one of the commonly used radioisotopes for prostate cancer treatment. The current irradiation technique used to produce this radioisotope suffers from several serious inherent drawbacks, of which one is the low beam current due to cooling limitation and the other is the electroplating process used to prepare the target. A liquid-metal jet impingement target cooling system developed at Soreq NRC demonstrated recently a cooling capacity of 8.4kW/cm2 while the pressure of the cooling liquid on the target back was less than 1bar. The latter value implies that the target can be made very thin and that the copper back-plate might be removed. Hence, we propose a new target design based on the use of a thin rhodium foil directly cooled by a liquid-metal such as gallium.

The flow structure of a bubble-driven liquid-metal jet in a horizontal magnetic field

Static magnetic fields are known to be suitable for damping mean flow and turbulent motion in an electrically conducting liquid. In this paper, an experimental study is presented considering the influence of a horizontal magnetic field on a bubble-driven flow of a liquid metal. The investigation is focused on the liquid circulation inside a liquid metal column driven by a central jet produced by gas injection. The fluid vessel has a circular cross-section and electrically insulating walls. Low gas flow rates were applied, resulting in a plume of separated bubbles rising inside a spot around the cylinder axis. This axisymmetric configuration is exposed to a horizontal magnetic field. We present detailed experimental data describing the spatial as well as the temporal structure of the velocity field. Measurements of the vertical and the radial velocity component, respectively, were performed using the ultrasound Doppler velocimetry (UDV), allowing for the first time a complete mapping of the liquid velocity distribution for a bubble-driven liquid metal flow. The magnetic field considerably modified the global and local properties of the flow field compared to an ordinary bubble plume. In the parameter range considered here we did not find a prior flow suppression, but, in fact, a restructuring of the convective motion. The original axisymmetric flow field became anisotropic with respect to the direction of the magnetic field lines. An upwards flow dominated in a plane parallel to the magnetic field, whereas the recirculating motion was enforced in the orthogonal plane. Contrary to usual expectations, the application of a moderate magnetic field (100 < Ha < 400, 1 ≲ N ≲ 10) destabilizes the global flow and gives rise to transient, oscillating flow patterns with predominant frequencies.

High heat-flux accelerator targets: Cooling with liquid metal jet impingement

In order to evaluate the performance of jet impingement for high heat-flux cooling, experimental cooling loops based on water and liquid metal jet impingement were designed and constructed. The current liquid metal system, based on an eutectic alloy of gallium and indium (GaIn) with a melting point of 15.7 °C, employs an annular inductive electromagnetic pump. The experiments showed that it is capable of accommodating a heat flux of about 20 MW/m 2 over an area of 10 −4 m 2. The jet velocity is less than 4 m/s and the required differential pressure from the pump is less than 10 5 Pa. In the present work the experimental section is supplemented by a theoretical one in which the cooling capability of impinging jets of liquid metal is modeled. In particular, turbulent flow in a dead end associated with the rear surface of a high-temperature target, and the corresponding heat-transfer process, are considered. The developed novel analytical model embodies the main peculiarities of the heat-transfer process and agrees fairly well with the experimental data. In addition, a detailed direct numerical simulation was done with the STAR-CD code. The gross underprediction of the turbulent heat transfer rate by the STAR-CD code is attributed to overprediction of the eddy viscosity in liquid metal flows.

MHD stabilities of liquid metal jet flows with gradient magnetic field

Liquid metal free surface flows (films, jets and droplets) are considered as prospective coolants in diverter/limiter system and first wall in fusion reactor, but the knowledge of liquid metal free surface, particularly jet flows, is very limited. In this article, the stability of a jet flow under a gradient magnetic field is investigated, and its MHD effects are the top concern. Firstly, a simplified model is developed to analyze the MHD effects of the jet flow and to explain the reason why it can keep stable, and the examination of the induced electric potential and currents of the jet flow is also included. Secondly, numerical simulation based on the approach of solving the electric potential equation was proceeded to support the theoretical analysis. Finally, experiments with different value of B 0 (maximum value of the magnetic field) and v 0 (average fluid velocity at the nozzle exit), and different kind of nozzle were performed on the Liquid Metal Experimental Loop (LMEL) in Southwestern Institute of Physics (SWIP), and there's a good agreement with experimental data and theoretical results. Qualitatively, a jet flow under a gradient magnetic field can keep its shape stable due to electromagnetic (EM) force in its direction and the compressed EM force in its cross-section, meanwhile, the reduction in velocity leads to a shorter range distance and a lager radius of cross-section of the jet flow. These effects are closely related to the parameters of the radius of the nozzle, the values of B 0 and v 0 .

3D MHD Jet in a Non-Uniform Magnetic Field

The purpose of this paper is to present a two-phase 3D magnetohydrodynamics (MHD) flow model that combines the volume of fluid (VOF) method with the technique derived from induced-magnetic-field equations for liquid metal free surface MHD-jet-flow. Analogy between the induced-magnetic-filed equation and the conventional computational fluid dynamics (CFD) equation is made, so that the equation can be conveniently accounted for by CFD. A penalty factor numerical method is introduced in order to force the local divergence-free condition of the magnetic fields and an extension of the void insulating calculation domain is applied to ensure that the induced-magnetic field at its boundaries is null. These simulation results for lithium liquid metal jets under magnetic field configurations of Magnetic Torus (Mtor) and National Spherical Torus Experiment (NSTX) outboard divertor have shown that three dimensional jet can not be annihilated by magnetic braking and its cross-section will deform in such a way that the momentum flux of the jet is conserved. 3D MHD effects from a magnetic field gradient cause return currents to interact with applied magnetic fields and produce unfavorable Lorentz forces. Under 3D applied non-uniform magnetic fields of the divertor, unfavorable Lorentz forces lead to a substantial change in flow pattern and a reduction in flow velocity, with the jet cross-section moving to one side of the jet space. These critical phenomena can not be revealed by 2D models.

High heat flux accelerator targets cooling with liquid-metal jet impingement

Accelerator targets for radioisotope production generate very high density of thermal energy in the target material, which absorbs the particles beam. The design of these targets requires efficient heat removal techniques in order to preserve the integrity of the target. Normal average heat fluxes from these targets are around 1kW/cm2 and may reach order of magnitude higher values at hot spots.Few techniques exist to deal with such high heat fluxes. One of them is jet impingement that has been proved to be able to deal with heat fluxes as high as 40kW/cm2 using water as coolant. However, this requires very high jet velocities of more than 100m/s. A few theoretical and experimental studies indicate that liquid-metal coolants (e.g., gallium or gallium alloys) can improve the heat transfer efficiency in this configuration.Experimental cooling loops based on water and liquid-metal jet impingement have been designed and built at Soreq to evaluate this method. For the current liquid-metal system an eutectic alloy of gallium and indium (GaIn) is used. Initial experiments demonstrate that the GaIn cooling system can deal with heat flux of about 2kW/cm2 over an area of 1cm2. The jet velocity is less than 4m/s and the required differential pressure from the pump is less than 1bar.

Microscopic high-speed liquid-metal jets in vacuum

The operation of microscopic high-speed liquid-metal jets in vacuum has been investigated. We show that such jets may be produced with good stability and collimation at higher speeds than previously demonstrated, provided that the nozzle design is appropriate and that cavitation-induced instabilities are avoided. The experiments with a medium-speed tin jet (u ∼ 60 m/s, Re=1.8×104, Z=2.9×10−3) showed that it operated without any signs of instabilities, whereas the stability of high-speed tin jets (d=30 μm, u=500 m/s, Re=5.6×104, Z=4.7×10−3) has been investigated via dynamic similarity using a water jet. Such a 500-m/s tin jet is required as the anode for high-brightness operation of a novel electron-impact X-ray source.

EFFECT OF OXIDATION ON THE BREAKUP AND MONOSIZED DROPLET GENERATION OF THE MOLTEN METAL JET

The objective of this study is to determine how breakup and monosized droplet generation of a molten metal (tin-lead, Sn63-Pb37) jet is affected by oxygen concentration. The major experimental equipment is the monosized droplet generator, which breaks up a laminar stream of liquid metal jet to produce monodispersed droplets by forced vibration generated from a piezoelectric disk within the proper frequency range. The results show that high oxygen concentration retards the breakup process of the molten metal jet, and the "critical oxygen concentration" is about 910 ppm at 1 atm and 350°C, which will result in sudden breakup failure. The molten metal jet can be further divided into three regimes, according to the effect of oxygen concentration, i.e., a "breakup regime," an "incomplete breakup regime," and a "breakup failure regime. "As long as a monosized droplet stream is formed, the breakup lengths of jets with different oxygen concentrations are almost the same, even when oxide islands appear. The behavior of the excited liquid metal jet still conforms to Rayleigh's theory, i.e., λmin = πD, and the working frequencies are limited within the range πD < λ < 2λopt, both when surface tension is up to 500 × 10-3 N/m, and when oxide islands appear, i.e., in both the breakup and incomplete breakup regimes. However, in the breakup failure regime, Rayleigh's theory is not applicable, andeven Wallace's surface tension reduction theory [12] cannot explain this reaction. It must be explained by integrating the combined research models of Haj-Hariri and Poulikakos [13] and Artem'ev and Kochetov [14], i.e., the oxide film islands grow and join until reaching high surface flexural rigidity at the critical oxygen concentration, which will suppress the capillary instability andresult in a sudden failure of the breakup process.

Micro Semi‐solid Manufacturing ‐ A New Technological Approach towards Miniaturisation

One of the most important prerequisites to meet the increasing demand for efficient technologies for micro‐part production is constituted by the ability to overcome existing process limitations by new innovative technological approaches. By the introduction of a new process variant based on a hybrid material condition between solid and liquid state, such an approach is presented. This micro semi‐solid manufacturing technology, so‐called Micro‐Thixoforming, was initiated, on the one hand, by being aware of the technological limits of existing micro‐forming and micro‐casting processes and, on the other hand, by a comprehensive understanding of the special rheological mechanisms of metallic materials in semi‐solid state finally establishing the desired potential to follow the trend towards miniaturisation with drastically reduced process restrictions. However, this promising potential can only be successfully exploited when the initial idea, which is based on phenomenological considerations, can be transferred to a process technology with sufficient practical relevance. Therefore, the presented new integrated process concept for Micro‐Thixoforming is particularly characterised by the application of unconventional solutions for the main process steps: raw material conditioning, thermal pre‐processing, semi‐solid forming and thermal post‐processing. To give an indication of the innovative character of the chosen practical solutions liquid metal jet technology, LASER‐induced plasma shockwaves and high pressure water jet should be mentioned. However, what is even more important in this context is the ability not only to realise a process concept but, beyond that, to recognise the further potential regarding new strategies for material design arising from the availability of this process. Such a strategy e.g. consists of utilising the well‐known segregation effect, which notably often is negatively associated with semi‐solid forming. However, for the envisaged technological approach, controlled segregation aims at a defined adjustment of functionally graded properties for the produced micro part.

Analysis on MHD Stability of Free Surface Jet flow in a Gradient Magnetic Fields

The simplified modeling for analysis on MHD stability of free surface jet flow in a gradient magnetic fields is based on the theoretical and experimental results on channel liquid metal MHD flow, especially, the results of MHD flow velocity distribution in cross-section of channels (rectangular duct and circular pipe), and the expected results from the modeling are well agreed with the recent experimental data obtained. It is the first modeling which can efficiently explain the experimental results of liquid-metal free surface jet flow.

Improving the Steel Ladle Lining at the Volzhskii Tube-Making Plant Joint-Stock Co.

Routes towards improving the quality of refractory lining for steel ladles and choice of the refractory product configuration are described. Periclase-carbon refractories of the mini-key format based on a composite carbon binder are shown to be the best choice for the steel ladle lining. Conditions for efficient performance (lining for the liquid-metal jet impingement zone, replacement of the nested block by a monolithic one, development of optimum block composition etc.) are discussed.

Liquid-tin-jet laser-plasma extreme ultraviolet generation

We demonstrate the applicability of liquid-metal jets in vacuum as regenerative targets for laser-plasma generation of extreme ultraviolet (EUV) and soft x-ray radiation. This extends the operation of liquid-jet laser-plasma sources to high-temperature, high-Z, high-density, low-vapor-pressure materials with new spectral signatures. The system is demonstrated using tin (Sn) as the target due to its strong emission around λ≈13 nm, which makes the material suitable for EUV lithography. We show a conversion efficiency of 2.5% into (2%BW×2π×sr) and report quantitative measurements of the ionic/atomic as well as particulate debris emission.

A shallow water model for the instability of a liquid metal jet crossed by an axial electrical current

A shallow water model for the instability of a liquid metal jet crossed by an axial electrical current

Liquid-metal-jet anode electron-impact x-ray source

We demonstrate an anode concept, based on a liquid-metal jet, for improved brightness in compact electron-impact x-ray sources. The source is demonstrated in a proof-of-principle experiment where a 50 keV, ∼100 W electron beam is focused on a 75 μm liquid-solder jet. The generated x-ray flux and brightness is quantitatively measured in the 7–50 keV spectral region and found to agree with theory. Compared to rotating-anode sources, whose brightness is limited by intrinsic thermal properties, the liquid-jet anode could potentially be scaled to achieve a brightness &amp;gt;100× higher than current state-of-the-art sources. Applications such as mammography, angiography, and diffraction would benefit from such a compact high-brightness source.

Experimental and Computational Simulation of Free Jet Characteristics Under Transverse Field Gradients

ABSTRACTIn this paper, we present numerical and experimental studies of the behavior of a liquid metal jet in a constant and gradient magnetic field. The experiments were conducted in the Magnetic Torus Liquid Metal MHD flow test facility (MTOR). The experimental results have shown that free jets can be stabilized by the magnetic field. The Lorentz force significantly suppresses the motion of the liquid metal jet and delays the break-up position. Analysis based on linear theory has been applied to understand jet behavior under magnetic fields. In addition, numerical simulation based on B formulation has been performed and compared to the experimental results.

Oxidation Effect on the Monosized Droplets Generation of the Liquid Metal Jet

The oxide formation on the surface of the molten metal jet was shown to have a drastic effect on the droplet formation process according to the description of some publication. Thus, the main objective of this research is to investigate the influence of oxygen concentration on the breakup and the monosized droplets generation of molten metal jet (Sn63 Pb37 alloy). The breakup phenomena of molten metal jet can be approximately divided into three regimes. They are “breakup regime” for oxygen concentration below C1, “transition regime” for oxgyen concentration between C1 and C2, and “breakup failing regime” for oxygen concentration beyond C2, respectively.

Modeling infinite/axisymmetric liquid metal magnetohydrodynamic free surface flows

Over the past several years, as part of the Advanced Power Extraction (APEX) project, liquid metal magnetohydrodynamic (MHD) film and jet flows have been modeled using the assumption of axisymmetry to simplify the governing equations to a more tractable two-dimensional (2D) form. The results of these 2D simulations as they pertain to liquid wall and divertor flows is presented here. The effect of toroidal field gradient on the flow thickness is shown to be rather small for thin fast first wall (FW) flows on electrically insulated backwalls, but streamwise currents generated by flow across the toroidal field gradient can interact with radial magnetic field components to produce toroidal motion with strong shear across the flow depth. The drag effects from flow across the toroidal field gradients become much stronger if thicker flows are considered. Concerns about surface stability due to forces trying to pull the liquid off the backwall also become much more severe for thicker flows or flows with conducting walls. Plans for continued work with three-dimensional models are discussed.

Ultrashort 1-kHz laser plasma hard x-ray source

We achieved a continuous, stable, ultrashort pulse hard x-ray point source by focusing 1.8-W, 1-kHz, 50-fs laser pulses onto a novel, 30-microm -diameter, high-velocity, liquid-metal gallium jet. This target geometry avoids most of the debris problems of solid targets and provides nearly 4pi illumination. Photon fluxes of 5x10(8) photons/s are generated in a two-component spectrum consisting of a broad continuum from 4 to 14 keV and strong K(alpha) and K(beta) emission lines at 9.25 and 10.26 keV. This source will find wide use in time-resolved x-ray diffraction studies and other applications.

Jet break up of liquid metal in twin fluid atomisation

For melt disintegration in spray forming and metal powder production, the liquid metal typically is atomised by means of twin fluid atomisation e.g. with inert gases. The first stage of the atomisation process is covered by the initialisation and development of surface perturbations on the liquid jet surface that subsequently grow and finally lead to the break up of the melt jet. The primary disintegration process affects all further stages of the atomisation process and hence influences the resulting spray characteristics. In this contribution, the influence of different material properties on the primary disintegration process of a metal melt in a free fall atomiser configuration is investigated. Surface instabilities of liquid metal jets up to the primary break up are analysed experimentally as well as analytically. Results of a linear instability analysis are discussed and compared to evaluations of high-speed video images. In comparison of both results the periodicity and main mechanism of the initialisation process is analysed.

Target studies for the neutrino factory at the Rutherford Appleton laboratory

Target studies at the Rutherford Appleton Laboratory have concentrated on studies of a solid heavy metal target. The suggestion to use a radiatively cooled target which rotates in beam was made shortly after the first NuFact workshop as a means of dissipating large amounts of power at a high temperature, and as an alternative to the proposed water-cooled rotating band and liquid metal jet targets. This paper examines the proposed drive scheme for the target ring, which uses induced currents and magnetic forces to both levitate and drive the target. Estimates of the power required to levitate and drive the target ring and the forces exerted on the moving ring as it enters the target capture solenoid are given.One of the principle concerns in the operation of a solid target is the severe shock stress experienced due to the impact of an intense energetic proton beam in a short time compared to the transit time of sound in the material. Calculations of the stresses induced in the target ring and their evolution with time as well as an initial estimation of the expected power densities and stresses in an existing high power density target are presented.