Showing papers on "Liquid metal published in 1973"

Theory of transport in liquid metals. I. Calculation of self‐diffusion coefficients

Abstract: An approach is presented for the theoretical calculation of self‐diffusion coefficients of liquid metals. The basic assumption is that the self‐diffusion coefficient of a liquid metal is equal to that of an appropriate hard sphere fluid. The hard sphere diameter is dependent upon temperature, and a method is developed for estimating this temperature dependence by exploring the relationship between the diameter and the interatomic potential energy function of the liquid metal. The theory gives accurate results for the magnitude and temperature dependence of the self‐diffusion coefficient for many liquid metals. In addition, the physical basis for the theory is consistent with what has been learned about the liquid state from molecular dynamics calculations.

Metal evaporation under powerful optical radiation

Abstract: The experimental results of our studies of metal evaporation under powerful optical radiation are presented. The theory of this phenomenon based on a liquid-vapor phase transition is developed. An approximate solution of the Clapeyron-Clausius equation is applied to the present problem. The method permits calculations of metal surface temperature versus incident light intensity I 0 . When a certain critical intensity is exceeded ( I_{md} \sim 10^{7}-10^{8} W .cm-2) a new effect is shown to arise due to disappearance of the metallic properties of the target. The new effect is a "transparency wave" in whose front a liquid metal turns into a liquid dielectric. For I_{0} > I_{md} it is the surface "transparent" (dielectric) layer that is evaporated. Its temperature is no longer raised and it remains below a critical value. This layer is separated from the metal by the transparency wave front, which propagates towards the interior of the metal. The transparency wave causes some other effects to arise, such as a sharp drop of the reflectivity from the metal surface, an essential change in the dependence of the observed evaporation front speed on I 0 , and, finally, occurrence of a maximum on the curve of specific recoil impulse versus I 0 . These other effects may be used to identify the transparency wave. The experimental results support some corollaries of our theoretical model. The vapor dynamics of metal evaporation under powerful millisecond optical radiation are investigated. Vapor heating near the target under laser light has been observed. The initial conditions of vapor motion are studied. From the gas-dynamic measurements the mass flow of the gas phase j 1 is calculated. The dependence of j 1 upon the incident light intensity is indicative of the fact that the metal surface has attained the temperature T = T_{md} , which corresponds to the liquid metal-liquid dielectric transition.

The thermal characteristics of the electroslag process

Abstract: The heat balance of a laboratory electroslag furnace working in quasisteady state is considered in detail. Results are presented for all possible melting mode combinations of direct and alternating (60Hz) current, with live and insulated molds, in air or argon atmospheres. The material studied is AISI 4340 steel, using a slag of CaF2 + 25 wt pct A12O3. The temperature and potential fields of the slag are determined, together with heat fluxes in the furnace. Heat balances are given for each subregion of the process, showing good agreement where results are available which permit cross checks of the balance. Suggested explanations are given for the differing behavior of the various melting modes based on variations in effective slag resistivity due to electrochemical reactions, and on variations in current path. The most important factors in determining the ingot heat balance are shown to be the electrode immersion, the slag volume’s dimensions, and the depth of the cylindrical liquid metal head on the ingot.

Corrosion and Deposition of Steels and Nickel-Base Alloys in Liquid Sodium

Abstract: The corrosion of materials by a liquid metal can be described in terms of the thermodynamics and kinetics of the several reactions that lead to transport of the corroded material into and through the liquid metal circuit. The thermodynamic driving force for liquid metal corrosion is the equilibration of the liquid metal and all surfaces in contact with it. The measured corrosion rate, therefore, represents the net sum of the rates of each of the many reactions continuously occurring in the system as the reactants attempt to reach simultaneous equilibrium. These equilibria include the solubilities of metals and nonmetals in sodium and their interactions both in the sodium and at the solid-liquid interface. Each of these corrosion reactions has its own characteristic kinetics, which, with diffusion and transport of the reactants and products through the liquid metal, give the overall rate of corrosion.

Thermal coupling device for cryogenic refrigeration

Abstract: Coupling between a refrigerant source and a device to be refrigerated is mechanically accomplished at room temperature by a liquid metal-filled bellows between the refrigeration source and the device. When the refrigeration source provides cooling, the liquid metal freezes to provide inter-engaging clamping force and a conductive thermal coupling.

Simple Mean-Field Approach to Phase Separation in Liquid-Metal Alloys

Abstract: A mean-field theory of phase separation in liquid-metal alloys is described. The method satisfactorily accounts for the variation of critical concentration in alloys of simple metals, and also gives critical temperatures in reasonably good agreement with experiment. It predicts that under pressure the critical temperature should rise proportionally to the ionic number density. The theory leads to typical mean-field divergences in the x-ray scattering intensity, specific heat, and temperature derivative of the resistivity. The relation between the instability that causes such divergences and the "freezing instability" described by Schneider et al. is discussed.

Self-diffusion in liquid tin and indium over extensive temperature ranges.

Abstract: The capillary-reservoir technique has been used to study the diffusion of Sn113 and Sb125 in liquid tin from 665°to 1746°K, and the self-diffusion of In114 from 621° to 1378°K. Multichannel scintillation radiotracer analyses were used to determine the total amount of diffusate migrating either into or out of a capillary tube. A definite wall effect was observed for In114 at 775°K. On the basis of the broad temperature range diffusivity data obtained, experimental criteria were established for very accurate measurement and calculation of liquid metal diffusivities using the capillary-reservoir technique. These criteria include: selection of the capillary tube material and diameter, determination of the magnitude of the △l effect, and careful identification of the radioisotopes employed in the determination of the diffusivities. It was found that the diffusion data do not fit any of the available theoretical models over the complete temperature range, nor any empirical relations of the formD =AT n. The observed nonlinear variation of logD vs logT was correlated with the disappearance of a second structure in the liquid state of tin.

Tin-lead purification of silicon

Abstract: Disclosed is a method of purifying silicon by introducing the silicon into liquid tin-lead alloy at a certain temperature. The silicon goes into solution with the tin-lead alloy, after which the temperature of the liquid metal solution is reduced to a temperature low enough to cause the solution to become super-saturated with respect to silicon which then solidifies as pure material. The solid pure silicon is withdrawn from the tin-lead solution leaving substantially all of the impurities behind.

Process for separating non-metallic inclusions from hot liquid metal

Abstract: The disclosure relates to a process for separating non-metallic inclusions from hot liquid metal, in particular from aluminum killed soft steel, in continuous casting plants, wherein the metal supplied into a tundish is guided at least once in upward direction to the surface of the metal sump in said tundish under formation of at least one stream at a speed greater than that of the metal in the tundish prior to its being deflected, whereby a wave is formed at the surface of the metal covered by slag The metal is guided towards the surface of the metal sump by means of a partition wall having at least one opening from which a canal extends in upward direction to end at a distance of from 3 to 30 cm below the metal sump surface

Electronic correlation functions at long wavelength in liquid metal alloys

Abstract: By using the condition of perfect screening in a liquid metal A-B alloy for ion A, ion B and electron e separately, the structure factors See, SAe and SBe in the long-wavelength limit are related to the measured partial structure factors of the ions, SAA, SBB and SAB. The relations are illustrated by calculating See, SAe and SBe for Na-K.

Temperature fields in liquid-metal-cooled rod assemblies

Abstract: BS>From 4th international seminar on heat and mass transfer in liquid metals; Trojir, Yugoslavia (6 Sep 1971). See CONFA survey is given of heat transfer in rod assemblies cooled by axial, turbulent flow of liquid metal. The discussion is restricted to steady-state conditions, uniform heat generation in the rods, and fully developed flow and heat transfer. Theoretical considerations center on turbulent transport characteristics and on methodology of computation. An outline of recent work in this area by the authors is included. (auth)

Statistical thermodynamics of the liquid surface

Abstract: The current theoretical situation regarding the structure of the liquid-vapour transition zone and the associated thermodynamic surface properties of simple liquids is reviewed. The thermodynamic and statistical mechanical treatments of the surface structure are assessed, and it is concluded that the former approach has limiting validity only as T→T crit. Liquid metal systems are discussed, together with the recent experimental evidence supporting the existence of stable density oscillations at the surfaces of certain liquid metals. The liquid inert gas systems, argon in particular, are considered in some detail, and a discussion of the statistical thermodynamics of the liquid 4He surface is given.

Heat sink cooled power semiconductor device assembly having liquid metal interface

Abstract: A power semiconductor device is bonded between thin metallic cup members and the edges of the assembly are provided with an electrical insulator to form the necessary creepage path. Liquid metal interfaces are provided between the cup members and heat sinks to provide high thermal and electrical conductivity joints therebetween. Since the liquid metal joint transmits heat and electricity, there is no need for high pressure joints, and since it does not permit a shear stress to be transmitted from the heat sink to the thin and fragile semiconductor device-cup member assembly, then the assembly is not stressed as with a high pressure joint. The excellent thermal characteristics of the joints result in reduced steady-state thermal resistance and improved transient response of the thin assembly and liquid metal interfaces.

Rotating gas jet apparatus for atomization of metal stream

Abstract: This method comprises striking a stream of liquid metal with a jet of gas which is rotated about the liquid metal stream so that it strikes the latter at an angle of between about 5* and about 90* with respect to the flow axis of the liquid stream to break up the liquid metal into small drops which solidify as a powder. The width of the gas jet is preferably less than that of the liquid metal stream. The rotational velocity of the gas jet about the liquid metal stream is sufficient to circle the liquid stream at least once before the latter moves out of the gas impingement zone. The apparatus employed comprises a vertically-aligned tube which is rotatably mounted in a stationary housing which, together, define an annular plenum chamber located concentrically about the tube. The wall of the rotatable tube defines an aperture which is angled between about 5* and about 90* with respect to the axis of the tube so that a stream of gas flowing therethrough is centered on the vertical axis of the rotatable tube along which liquid metal is gravity flowed from a pour cup positioned above the rotatable tube. As the latter is rotated, a gas is flowed into the plenum chamber and through the angled tube aperture to strike the liquid metal stream flowing downwardly through the tube. The resulting fine metal particles are collected after solidification in a chamber placed below the rotatable tube.

Control method and apparatus for the production of powder metal

Abstract: Control of the process for producing pre-alloyed metallic powder by controlling the melting rate of at least one consumable electrode formed from an ingot of the metal to be ultimately atomized, to produce a controllable continuous flow of metal for atomization into powder. After striking an arc for melting the electrode which is located in a chamber containing a protective atmosphere, the power input to the electrode is selectively adjusted during continual melting to control the melting rate to equal the optimum rate of atomization. The liquid metal droplets from the electrode are collected in a preheated holding reservoir to provide a homogeneous stream of metal which is delivered to a disintegrator. This produces an atomized liquid metal which solidifies into a powdered form and is collected.

Void Fraction and Pressure Drop in Liquid Metal Two-Phase Flow

Abstract: This paper describes a new correlation for predicting a two-phase frictional pressure drop multiplier, and discusses the pressure level effects and the mass velocity effects. This correlation predicts satisfactorily the frictional pressure drop not only for liquid metals but also for ordinary fluid two-phase flow in a wide range of flow variables. The authors' void fraction correlation previously proposed is also compared with published data of void fraction for liquid metal two-phase flow, and is found to represent well the mass velocity effects. Wettability and magnetohydrodynamic effects are discussed briefly in relation to the hydrodynamic characteristics of liquid metal two-phase flow.

Possibility of electromagnetic self-excitation in liquid metal flows in fast reactors

Abstract: The possibillty that the liquid metal flows in fast reactors may form electromagnetically self-exciting systems are examined and the potential consequences are considered. Simple calculations indicate that the smaller prototypes are unlikely to self-excite, but there is a possibility that the larger ones might. The pumps appear more likely to self-excite than the reactor flow systems as a whole. Lengthy calculations would be needed to establish definitely whether the flow regimes in the reactors are self-exciting or not. (auth)

Method of dispensing low velocity liquid material for strip casting

Abstract: Liquid materials are dispensed at a low velocity through the use of a multi-chambered tundish which induces a dampening effect upon the flow of the liquid material which passes through the tundish. The tundish is well suited as a liquid metal source in continuous strip casting methods.

Frictional Pressure Drop for NaK-N2 Two-Phase Flow in Rectangular Cross Section Channel of Large Aspect Ratio

Abstract: In this paper, the frictional pressure drop in an isothermal liquid metal-gas two-phase flow through a rectangular channel with large width-to-height ratio is treated semiempirically for a NaK-N2 two-phase flow system. The frictional pressure drop in the two-phase flow is compared with the following two reference values : 1. The frictional pressure drop in the liquid flowing alone in single phase with the same velocity as that of the liquid in the two-phase mixture. 2. The frictional pressure drop in the liquid flowing alone in single phase with the same mass flow rate as that of the liquid in the two-phase mixture. The comparison with the former reference value is necessary for the prediction of friction loss in a liquid metal MHD generator channel whose medium would be two-phase mixture. The semiempirical analysis was performed assuming the two-phase mixture to be a continuous medium with its properties, e.g. viscosity and density, defined by void fraction and the velocity determined by the total mass f...

Magnetic apparatus for metal casting

Abstract: Apparatus for metal casting using a magnetostatic field generator having at least one superconducting solenoid magnet disposed on at least one side of a mould or metal shell for setting up a heterogenious magnetostatic field of intensities at least in excess of 10,000 gauss in the liquid metal retained within the mould or metal shell to thereby agitate the liquid metal. The mageto-static field generator is accommodated within a cryostat, which is always held cool at a predetermined temperature by a special auxiliary cooling means.

Method and apparatus for continuous casting of metal with a considerably lower specific gravity of the strand in relation to the cast metal

Abstract: A method of, and apparatus for, continuous casting of metals with considerably lower specific gravity of the strand in relation to the cast metal, wherein the metal and the additive constituents in the liquid metal pool are introduced into a hollow mold compartment. As the additives there are added porous bodies having a specific gravity less than 1, and upon the porous bodies there is exerted a pressure which at least corresponds to the magnitude of the lift force acting upon the porous bodies upon penetration into the metal. The apparatus for the performance of the method aspects comprises means defining a hollow mold compartment and an infeed device for the metal. In addition to the infeed device for the metal there is provided a device for exerting a pressure upon the porous bodies for infeeding the porous bodies into the liquid metal pool.

The influence of gas phase resistance on mass transfer to a liquid metal

Abstract: When a dilute gas is absorbed in a liquid metal in which Sievert’s law is obeyed, the gas phase resistance is likely to be significant. The influence of gas phase resistance will de-pend on the concentration of the transferred species in both the gas and the liquid as well as on the mass transfer coefficients in both the gas and liquid phases. An overall mass transfer coefficient is defined by: n″(X)1=kov√pb -cb and equations are developed relating this to the variables mentioned. Experimental work has been carried out with dilute oxygen jets (p(O2) = 0.1 and 0.2 atm) blowing onto molten silver, and the results have confirmed that the resistance in the gas phase contributes to the overall resistance. From these results it has been possible to estimate gas phase mass transfer coefficients which range from 1.4 cm/s for a jet momentum of 8000 dyne and lance height of 18.5 cm to 4.8 cm/s for a jet momentum of 56,000 dynes and lance height of 10.5 cm.

Dnb in liquid metal heated forced convection boiling

Abstract: (Received 28 d4urch 1973 and in r~~~~~ 4 May 1973) Abstract-An experimental program was performed to investigate departun from nucleate boiling (DNB) in a flow boiling system heated by a liquid metal flow. The boiling fluid, freon 12, was circulated vertically upward and was heated by countetmurent flowing mercury. Magnitudes and trends of the heat flux and quality at DNB were compared to data obtained on a similar experimental faciIity employing uniform electrical heating of the test section wall. The results show that at a given quality, the magnitude of the DNB heat flux is larger in the case of uniform electrical heating. This result is not predicted by a DNB correlation based on' data obtained from electrically heated test sections employing uniform and non- uniform axial heat flux distrib&ons. It is demonstrati that the DNB phenomenon in a temperature controkd systan (liquid metal heated) may not be well predicted from correlations based on data funiformiy or nonuniformly heated) obtained from heat flux controlled systems (eiectrically heated).

Gas void detector for liquid metal

Abstract: Detection of gas voids in a liquid metal is accomplished by pumping the liquid metal through a flowmeter with an electromagnetic pump. The flowmeter measures the rate of flow of the liquid metal which decreases with the presence of gas voids in the liquid metal. When the flow rate is reduced because of the presence of such gas voids an alarm signal is generated.

Apparatus for the production of laser radiation from a metal vapor

Abstract: Disclosed is a technique for producing vapors of metals in containment vessels that experience the melting temperature but not the boiling temperature of the metal being vaporized. The metal is maintained in molten pools by the containment vessel. Pumping means such as wicks transfer the metal from the pools to a higher temperature region internal of the containment vessel where the liquid metal is boiled into a vapor. The generation of laser radiation from an excited metal vapor produced in this manner is also disclosed.