Showing papers on "Liquid metal published in 2003"

Generation of Droplets in Slag-Metal Emulsions through Top Gas Blowing

Abstract: The behavior of metal droplets in a slag-metal-gas emulsion through impinging gas blowing was investigated experimentally using a cast iron-slag-nitrogen gas system at high temperatures. A mathematical model of the emulsification process for determining the generation rate, size distribution, and residence time of metal droplets has been developed and successfully validated using experimental data. From the present work, it was found that the generation rate and size distribution of metal droplets is strongly influenced by the ratio of the inertial force of blown gas to the surface tension and buoyancy forces of the liquid metal. A new dimensionless number, i.e. blowing number, which represents the ratio of inertial to surface tension and buoyancy forces and also the departure of the system from its stable condition defined by the Kelvin-Helmholtz criterion, is proposed. A functional relationship of generation rate and size distribution of metal droplets with the blowing number is proposed.

Alloying element vaporization during laser spot welding of stainless steel

Abstract: Alloying element loss from the weld pool during laser spot welding of stainless steel was investigated experimentally and theoretically. The experimental work involved determination of work-piece weight loss and metal vapour composition for various welding conditions. The transient temperature and velocity fields in the weld pool were numerically simulated. The vaporization rates of the alloying elements were modelled using the computed temperature profiles. The fusion zone geometry could be predicted from the transient heat transfer and fluid flow model for various welding conditions. The laser power and the pulse duration were the most important variables in determining the transient temperature profiles. The velocity of the liquid metal in the weld pool increased with time during heating and convection played an increasingly important role in the heat transfer. The peak temperature and velocity increased significantly with laser power density and pulse duration. At very high power densities, the computed temperatures were higher than the boiling point of 304 stainless steel. As a result, evaporation of alloying elements was caused by both the total pressure and the concentration gradients. The calculations showed that the vaporization occurred mainly from a small region under the laser beam where the temperatures were very high. The computed vapour loss was found to be lower than the measured mass loss because of the ejection of tiny metal droplets owing to the recoil force exerted by the metal vapours. The ejection of metal droplets has been predicted by computations and verified by experiments.

Thermocapillary flow and rupture in films of molten metal on a substrate

Abstract: We consider fluid flow in thin films of molten metal resulting from irradiation by a Gaussian laser beam. Surface tension gradients due to nonuniform heating induce a flow of the molten liquid away from the center of the irradiated area, leading to formation of dry areas on the substrate. We develop a mathematical model of the flow under the assumption of the large ratio of laser beam radius to film thickness. The model extends the standard lubrication-type analysis to include the highly nonlinear dependence of evaporative flux on local interfacial temperature, unsteady heat conduction in the substrate, and positive disjoining pressure due to unbalanced contributions from the kinetic energy of free electrons in the metal. The latter is proportional to the inverse square of the film thickness. We identify thermocapillary stresses as the main mechanism of rapid removal of liquid metal from the irradiated area. Characteristic times of the process, as well as shapes of the molten region surface, agree with experimental observations. We investigate rupture of the molten film and find two different rupture scenarios. The melt surface can either touch the substrate at a point (point rupture) or along a line at a certain radial distance away from the center of the irradiated area (ring rupture). Nondimensional criteria for these two mechanisms are identified. In particular, we show that positive disjoining pressure promotes ring rupture.

The liquid surface/interface spectrometer at ChemMatCARS synchrotron facility at the Advanced Photon Source

Abstract: We discuss results from the first experiments on a new liquid surface/interface X-ray spectrometer recently commissioned by ChemMatCARS at Sector 15 of the Advanced Photon Source. These experiments include studies of liquid/liquid interfaces, monolayers supported on the water surface, and liquid metal surfaces.

Measurement of Pressure Drop in a Full-Scale Fuel Assembly of a Liquid Metal Reactor

Abstract: An experimental study has been carried out to measure the pressure drop in a 271-pin fuel assembly of a liquid metal reactor. The rod pitch to rod diameter ratio~ P/D! of the fuel assembly is 1.2 and the wire lead length to rod diameter ratio~H/D! is 24.84. Measurements are made for five different sections in a fuel assembly; inlet orifice, fuel assembly inlet, wire-wrapped fuel assembly, fuel assembly outlet and fuel assembly upper region. A series of water experiments have been conducted changing flow rate and water temperature. It is shown that the pressure drops in the inlet orifice and in the wire-wrapped fuel assembly are much larger than those in other regions. The measured pressure drop data in a wire-wrapped fuel assembly region is compared with the existing four correlations. It is shown that the correlation proposed by Cheng and Todreas fits best with the present experimental data among the four correlations considered@DOI: 10.1115/1.1565076# The liquid metal reactor core consists of several fuel assemblies contained in a hexagonal shaped duct. There is no flow exchange between ducts. In order to efficiently extract the heat generated in a fuel assembly, it is important to distribute the flow rate among the fuel assemblies and to maintain the temperature distribution properly. The distribution of coolant flow rate in each fuel assembly is determined by the heat generation in each fuel assembly after the required whole coolant flow rate is determined to meet the reactor power. The reactor core is divided into a certain number of groups that have the same coolant flow rate, and then the temperature distribution of the fuel assembly is calculated and the coolant flow rate in each group is adjusted to have the same degree of peak temperature in the fuel rod. Then, the orifice in the bottom region of the fuel assembly is designed following the pressure drop of the fuel assembly. Thus, the information of pressure drop in a fuel assembly is very important in the thermal hydraulic design of the reactor core. The individual fuel assembly consists of inlet orifice, fuel assembly inlet, wire-wrapped fuel assembly, fuel assembly outlet and fuel assembly upper region. The primary objective of the present study is to measure the pressure drops in these regions for the design of Korea Advanced Liquid Metal Reactor ~KALIMER!. A series of experiments are conducted to measure the pressure drops in these regions. The relative magnitude of pressure drops in these regions is investigated from the measured data. As will be shown later, the pressure drops in the inlet orifice and in the wire-wrapped fuel assembly is much larger than the pressure drops in other regions. The design of the inlet orifice for KALIMER is not determined yet and the inlet orifice used in the present measurement is only a tentative design. Thus, the primary emphasis of the present study is placed on the analysis of pressure drop in the wire-wrapped fuel assembly. In order to maintain a proper spacing between fuel pins and promote the coolant mixing, several types of spacers are proposed. Among the various spacers the helical-type wire-spacers are widely used in the liquid metal reactor ~LMR! and are adopted in the design of KALIMER. However, the existence of spacers between fuel pins causes the increase of hydraulic resistance,

Numerical Approach to the Safety Evaluation of Sodium—Water Reaction

Abstract: A numerical simulation method of multi-dimensional and multi-phase reacting flow (SERAPHIM code) has been developed to evaluate the sodium-water reaction (SWR) phenomena in a steam generator of liquid metal fast reactor (LMFR). A compressible multi-fluid and one-pressure model is adopted and pressure and velocity fields are updated simultaneously by the HSMAC method. Two types of reaction models are considered; one is a surface reaction and the other is a gas-phase reaction. The surface reaction model assumes that water vapor reacts with the liquid sodium at the gas-liquid interface. If chemical reaction heating is large enough, liquid sodium is vaporized resulting in a gas-phase reaction. In the surface reaction, the reaction rate is assumed to be infinitely large. Several overall reaction equations are taken into account in the gas-phase reaction and the reaction rates are described in the form of the Arrhenius law. In the present study, adequacy of the analytical procedures for compressible multi-phase flow is validated by a benchmark calculation of the Edwards pipe blowdown problem. As a numerical example, two- and three-dimension analyses of the single-tube geometry and the two-dimension analyses of the 43-tubes geometry are carried out. It is concluded that the numerical quantification of the SWR accident by the SERAPHIM code is practicable and further use of the SERAPHIM code is useful to resolve safety issues immanent in the SWR.

Constrained filament niobium-based superconductor composite and process of fabrication

Abstract: A niobium-based superconductor is manufactured by establishing multiple niobium components in a billet of a ductile metal, working the composite billet through a series of reduction steps to form the niobium components into elongated elements, each niobium element having a thickness on the order of 1 to 25 microns, surrounding the billet prior to the last reduction step with a porous confining layer of an acid resistant metal, immersing the confined billet in an acid or a high temperature liquid metal to remove the ductile metal from between the niobium elements while the niobium elements remain confined by said porous layer, exposing the confined mass of niobium elements to a material capable of reacting with Nb to form a superconductor.

Examination of liquid metal surfaces through angular and energy measurements of inert gas collisions with liquid Ga, In, and Bi

Abstract: Gas–liquid scattering experiments are used to measure the recoil directions and energies of neon, argon, and xenon atoms scattering from liquid gallium, indium, and bismuth. The angular and energy distributions vary systematically with the identity of the gas and liquid and with the incident gas energy and liquid temperature. We find that the gas atoms scatter into a narrower angular range from liquids with higher surface tension γ (γGa>γIn>γBi), while they transfer less energy to liquids of higher atomic mass (mBi>mIn>mGa). Comparisons of the angular distributions with scattering models suggest that lower surface tension liquids possess atomically rougher surfaces that redirect impinging atoms more broadly into space. The trend we observe linking broader angular distributions with lower energy transfer appears to be a microscopic manifestation of a general trend between decreasing surface tension and increasing atomic mass for main group metals such as Ga, In, and Bi.

Numerical Simulation of the Liquid Flow Into a Porous Medium with Phase Change: Application to Metal Matrix Composites Processing

Abstract: A method of metal matrix composites processing consists of injecting a liquid metal through a fibrous preform. The metal flow through the porous preform is associated with phase-change phenomena which imply modifications of the porous medium permeability and disturb the metal flow. A finite-volume model was developed to simulate the injection of a pure metal through a fibrous preform placed between two plane walls of a metal mold. This model is based on the simultaneous resolutions of the heat equation, Darcy's law, and an advection equation to follow the evolution of the metal front geometry during the infiltration.

Water large leaks into liquid Pb–17Li: first experimental results on LIFUS 5 facility

Abstract: Since several years ENEA is involved in experimental activities concerning the interaction between molten lithium lead alloy, in eutectic composition, and pressurised water in conditions relevant for DEMO fusion reactor, in order to predict the behaviour of a WCLL blanket module in case of an in blanket LOCA. In this ambit LIFUS 5 apparatus was designed and constructed to carry out the experimental campaign on water large leaks into liquid Pb–17Li, with the final aim to provide data for the validation of the mathematical modelling of the related phenomena. After two tests performed to qualify all mechanical components and the data acquisition system, LIFUS 5 was operated at the ENEA C.R. Brasimone for tests nos. 3 and 4. Water was injected into the reaction tank at a pressure of 155 bar with two different values of sub-cooling. The initial liquid metal temperature was fixed to 330 °C. The first pressure peak due to the water vaporization and jet expansion was clearly recognized together with the subsequent pressure increase due to further water injection and hydrogen generation. In the performed experiments the maximum pressure peak, as detected in both reaction and expansion vessels, never overcame the value of the injected water. Moreover, in these two tests a significant temperature increase in the reaction vessel occurred, strictly connected to the amount of injected water.

Method and apparatus for maintaining a liquid metal switch in a ready-to-switch condition

Abstract: A method and apparatus for maintaining a liquid metal switch in a state of readiness for switching. The liquid metal switch has a liquid metal volume contained in a cavity of a switch body. A signal path though the cavity is made or broken by energizing an actuator to move the liquid metal volume within the cavity in response to a switching signal. To maintain readiness, a signal generator supplies a vibratory signal to the actuator. The resulting vibrations in the liquid metal volume allow the liquid metal volume to be subsequently moved with reduced power.

Device for generating x-rays having a liquid metal anode

Abstract: The invention relates to a device for generating X-rays (31). The device has a source (5) for emitting electrons (27) accommodated in a vacuum space (3). The X-rays are emitted by a liquid metal as a result of the incidence of the electrons. The liquid metal flows through a constriction (13) where the electrons emitted by the source impinge upon the liquid metal. The constriction is bounded by a thin window (23), which is made from a material which is transparent to electrons and X-rays and which separates the liquid metal in the constriction from the vacuum space. According to the invention, the constriction (13) has a cross-sectional area which, seen in a main flow direction (X), increases in such a manner that during operation in said direction, a decrease of a flow velocity takes place such that a decrease of a pressure of the liquid metal in the constriction in said direction, caused by viscous flow losses, substantially corresponds with an increase of said pressure in said direction, which is caused by the Bernoulli effect resulting from said increase of the velocity. As a result, the pressure of the liquid metal in the constriction can be maintained at a uniform relatively low level throughout the constriction, so that a uniform and relatively low mechanical load is exerted on the window during operation. In this way, the deformation of the window and the risk of breakage of the window are considerably limited.

Grain boundary liquid metal wetting: A synchrotron micro-radiographic investigation

Abstract: The penetration of liquid metals into the grain boundaries (GB) of solid metals can lead to severe embrittlement of the solid. Grain boundary wetting, which is the precursor process of liquid metal embrittlement, is still far from being well understood. We report in situ observations of the propagation kinetics of liquid metal into the GB of bicrystals and polycrystals. The experiments are performed using synchrotron radiation micro-radiography. This imaging technique is well adapted for the in situ non-destructive bulk characterization of such phenomenon due to suitable spatial and temporal resolutions. Experiments have shown that the Ga penetration front in aluminum bicrystals propagates roughly with linear time dependence, whereas a discontinuous behaviour occurs in polycrystals. � 2002 Elsevier Science B.V. All rights reserved.

Low-pressure corium dispersion experiments with simulant fluids in a scaled annular cavity

Abstract: Experiments were performed in a scaled annular cavity design, to investigate melt dispersal from the reactor pit when the reactor pressure vessel (RPV) lower head fails at low system pressure of less than 2 MPa. The fluid dynamics of the dispersion process was studied using model fluids, water, or bismuth alloy instead of corium, and nitrogen or helium instead of steam. The effects of different breach sizes and locations and different failure pressures on the dispersion were studied, specifically by testing central holes, lateral holes, horizontal rips, and complete unzipping of the bottom head.With holes at the base of the bottom head, the most important parameters governing the dispersion of melt are the hole size and the burst pressure. The fraction dispersed into the reactor compartments increases with larger holes and higher pressures. Values up to 76% have been found for both melt simulant liquids, water, and metal. With lateral breaches the liquid height in the lower head relative to the upper and lower edge of the breach is an additional parameter for the dispersion process, and usually not all the liquid is discharged out of the RPV. The liquid fraction entrained out of the RPV can be higher withmore » a small breach than with a large one because of the longer blowdown time. With lateral failures, maximum dispersed fractions of 50% were found with water as melt simulant and less than 1% with liquid metal. It follows from similarity considerations that the results from the liquid metal tests represent the lower bound for the dispersed melt fractions; however, they are probably closer to the expected values than the results from the water tests, which represent the upper bound. So, significantly less dispersion of melt can be expected for lateral breaches at pressures below 2 MPa, probably less than 10%. If higher dispersion occurs, due to higher pressure at failure or with failures near the bottom center, simple devices to reduce the dispersion out of the cavity may be feasible.« less

The application of gallium as a liquid metal lubricant

Abstract: The application of Ga as a base for a solid metal lubricator has been considered. Different methods were applied to investigate properties of liquid Ga in the temperature range 30–300°C. Some peculiarities of liquid Ga can be explained with structural transformations. It has been shown that Ga is characterized with combination of a high plasticity and strength of a melt. Due to the good adhesion, Ga forms stiff films on the surface of contact bodies. A mixed mode of friction usually exists when Ga is applied as a solid lubricator. Moreover, the friction process is characterized with low friction coefficients, which practically do not depend on load and velocity. Investigations have revealed that Ga is a promising metal for solid lubricators. Properties of these lubricators can be easily controlled by the preparation of suspensions on the base of Ga.

Numerical Simulation of Non-Premixed Diffusion Flame and Reaction Product Aerosol Behavior in Liquid Metal Pool Combustion

Abstract: In the present study, a numerical methodology has been developed to solve a non-premixed diffusion flame under natural convection. The methodology has been applied to the calculation of the liquid sodium pool combustion experiment at various pool temperatures and oxygen molar fractions. The authors have proposed expressions of aerosol dynamics, radiation heat transfer and evaporation of liquid sodium that are applicable to sodium combustion phenomena. The computations reproduce the experimental observations concerning burning rate, flame temperature and flame height, consistently. The aerosol release fractions are also in good agreement with the measurement. Dominant mechanisms of the mass and heat transfer are identified through the numerical simulation. An intrinsic feature found in the present study is that the liquid sodium pool combustion is self-limited and a negative feedback mechanism is at work. Interaction among the thermal-hydraulics, chemical reaction and aerosol dynamic behavior plays an important role in the phenomena and it has been successfully analyzed by the numerical simulation. The present method can be used to understand sodium combustion phenomena and applied to the modeling of sodium pool combustion for safety analyses of liquid metal fast reactors. The numerical simulation is a useful tool because it can easily employ various conditions by changing parameters.

Semi-Solid Slurry Formation Via Liquid Metal Mixing

Abstract: New, economical semi-solid metal (SSM) processes rely on forced convection during solidification to influence non-dendritic growth. The fundamental mechanisms that produce SSM microstructures in the presence of forced convection (due to fluid flow) are not fully understood. The objective of this work is to elucidate these mechanisms through the use of a new semi-solid slurry-making technique. Employing an apparatus developed at WPI, two alloy melts are mixed within a static reactor that induces convection and rapid cooling. Experiments carried out with this apparatus, named the “Continuous Rheoconversion Process” (CRP), result in globular semi-solid microstructures throughout a wide range of processing conditions. These conditions include the superheat in the melts before mixing, cooling rate of the slurry through the SSM range, and the presence or absence of inoculants in the melts. The results comprise repeatable sets of semi-solid microstructures having fine particle size and shape factors approaching unity. Even in the absence of melt inoculants, uniform distributions of α-Al particle sizes of about 60μm are attainable. Entrapped liquid is not present in the majority of the samples obtained with the CRP, and irregular particles that form in the process are of a limited distribution. Variation of slurry analysis methods indicates that these structures can be obtained consistently for both thixocasting and rheocasting applications. The design of the mixing reactor leads to turbulent fluid flow just as solidification commences. The results suggest that the following factors must be considered in identifying the mechanisms operating under the above conditions: copious nucleation of the primary phase; dispersion of nuclei throughout the bulk liquid; and

Separation system of metal powder from slurry and process

Abstract: A system and method of separating metal powder from a slurry of liquid metal and metal powder and salt is disclosed in which the slurry is introduced into a first vessel operated in an inert environment when liquid metal is separated from the metal powder and salt leaving principally salt and metal powder substantially free of liquid metal. The salt and metal powder is transferred to a second vessel operated in an inert environment with both environments being protected from contamination. Then the salt and metal powder are treated to produce passivated powder substantially free of salt and liquid metal. The method is particularly applicable for use in the production of Ti and its alloys.