Showing papers on "Liquid metal published in 1994"

Thermodynamic properties of Pd40Ni40P20 in the glassy, liquid, and crystalline states

Abstract: Bulk specimens of the easy glass‐forming alloy Pd40Ni40P20 have been undercooled consistently into the glassy state at cooling rates as low as 10 K/min applying the melt‐fluxing technique in boron trioxide. Due to this low cooling rate, heat capacity measurements could be performed in a commercial heat‐flow differential calorimeter, covering for the first time the entire undercooling regime of a liquid metal from the melting temperature down to the glass transition temperature. Based on the measured specific heat data of the undercooled liquid and the crystalline state, the differences in the thermodynamic functions enthalpy, entropy, and Gibbs free energy are determined in dependence on temperature. The entropy balance yields a value of T0=500±5 K for the ideal glass transition temperature of this metallic system. The experimental values are compared to the corresponding thermodynamic functions, derived from commonly applied Gibbs free energy approximations for the undercooled liquid.

Application of Pinch Force to the Separation of Inclusion Particles from Liquid Steel

Abstract: The pinch force which is one of the most common electromagnetic forces in the metallurgical field can be generated by imposing an electrical current on a liquid metal. In this force field, electrically nonconductive particles suspended in a liquid metal experience a force in the opposite direction to the pinch force, and are squeezed out from the liquid metal. In this study, the above principle was applied to the separation of nonmetallic inclusion particles from liquid steel. Firstly, the separation efficiency, η, of nonmetallic inclusion particles from the liquid steel flowing in a circular pipe was calculated by the trajectory method under laminar flow conditions. The value of η was found to be a function of VR, (CIDR2/Re)Z and r1/δ, where r1 is the radius of the pipe, δ is the skin depth and VR, CI, DR, Re and Z are nondimensional parameters. The estimated value of η is a continuous casting tundish equipped with a channel-induction furnace was greater than 95% for particles with a diameter over 60 μm. Secondly, the value of η for a square pipe was computed by the concentration method. In this case, the value of η was found to be a function of V'R and (CIDR2/Re)Z at x1/δ=0, where x1 is the half width of the square pipe. However, with increasing x1/δ, secondary flows appeared in a cross section of the pipe because of the skin effect. These flows were found to increase the value of η by transporting the particles in the inner region toward the wall.

Heat-resistant broad-bandwidth liquid droplet generators

Abstract: Apparatus and methods for making uniformly-sized and predictably-spaced droplets from high-temperature liquids. Liquid droplet generators having electromechanical driving elements are coupled to a power supply to apply pulsed excitation forces through a wall of a delivery tube to a high-temperature liquid, e.g., a liquid metal, epoxy, or polymer. The excitation forces generated by the driver induce capillary vibrations in the liquid within the delivery tube. Liquid jet streams having capillary vibrations when exiting an orifice break up into groups of substantially uniformly-sized liquid droplets shortly after leaving the orifice. Droplets may be produced in a uniformly-spaced series, or individually on demand in response to a single burst of force from the driving element. A heat source is also thermally coupled to the delivery tube to maintain the liquid in a high-temperature state. Embodiments using heat-sensitive elements thermally insulate those elements from the wall of the heated delivery tube and may also actively cool the elements by one or more heat exchangers. A magnetohydrodynamic embodiment couples a magnetic field, having spaced points of maximum intensity, to a fluid stream exiting an orifice, causing the stream to break into droplets in response to the periodic magnetic field.

Liquid metal heat conducting member and integrated circuit package incorporating same

Abstract: An integrated circuit package (10) has an integrated circuit chip (11), a substrate (12) which holds the chip, and a novel heat conduction mechanism (15) which is coupled to the chip (11) and which provides a path (through 13 and 14) for conducting heat from the chip to a fluid medium. This heat conduction mechanism is characterized as including (a) a compliant body (15b), having microscopic voids throughout, which is disposed in and fills a gap (G) in the heat conducting path, and (b) a liquid metal alloy (15b) that is absorbed by and partially fills the microscopic voids of the compliant body. Due to the presence of the liquid metal alloy, the thermal conductivity through the body is high. Also, due to the voids in the body being only partially filled with the liquid metal alloy, the body can be compressed by dimensional variations within the integrated circuit package without squeezing out any of the liquid metal alloy that is held therein.

Fundamental characteristics of molten metal flow control by linear induction motor

Abstract: Molten metal flow control using linear induction motor is expected much to be a new revolutionary basic technology to realize high quality and low cost processes. We report an experiment with fused metal (melting point: 45/spl deg/C) and 100 kg molten steel. According to the fused metal experiment, the linear induction motor has a good ability for stopping and acceleration as well as braking of metal flow. However, the electromagnetic force to be able to stop the metal flow in vertical arrangement is several times larger than the one in horizontal arrangement because of the liquid metal effect. A resonance condenser is useful to reduce the required power source capacity. Therefore, to control the molten metal flow, voltage (current) regulation is superior to frequency regulation. Though the large air gap also makes the electromagnetic force reduced, a conductive shorting bar (Z/sub r/B/sub 2/), installed inside the non-conductive firebrick, increases the electromagnetic force. >

Oxygen mass transfer at liquid-metal-vapour interfaces under a low total pressure

Abstract: The problem of oxygen exchange at the interface between a gas and a liquid metal is treated for systems under a “vacuum” (Knudsen regime, pressures lower than 1 Pa), where, due to the large mean free path of gas molecules in a vacuum, transport processes in the gas phase have no influence on the total interphase mass exchange, which is controlled by interface phenomena and by oxygen partition equilibrium inside the liquid. Owing to the double contribution of molecular O2 and volatile oxides to the oxygen flux from the surface, non-equilibrium steady-state conditions can be established, in which no variations in the composition of the two phases occur with time, as the result of opposite oxygen exchanges. The total oxygen and metal evaporation rates are evaluated as a function of the overall thermodynamic driving forces, and an account of the transport kinetics is given by using appropriate coefficients. A steady-state saturation degree s r, is defined which relates the oxygen activity in the liquid metal to the O2 pressure imposed and to the vapour pressures of volatile oxides. When metals able to form volatile oxides are considered, pressures of molecular O2 higher than those defined under equilibrium conditions have to be imposed in the experimental set-up in order to obtain a certain saturation degree, as a consequence of the condensation of the oxide vapours on the reactor walls. Effective oxidation parameters are determined, which define the conditions leading the liquid to a definite steady-state composition under a “vacuum” when it is out of equilibrium. The effective value of the oxygen pressure which corresponds to the complete oxygen saturation of the metal, $$P_{O_{2,} s}^E $$ , is evaluated at different temperatures for the systems Si-O and Al-O. The results are represented as curves of $$P_{O_{2,} s}^E $$ against T, which separate different oxidation regimes; these results agree well with the experimental data found in the literature.

Action of pulse magnetic field on molten metal

Abstract: Effect of pulse magnetic field on two-phase zone of crystallizing metal has been investigated by methods of mathematical modelling in reference to vertical continuous casting machine. On the first step of the investigation electromagnetic problem for penetration of pulse magnetic field of cylindrical inductor in depth of liquid metal has been solved and distribution of electromagnetic forces in the melt has been obtained at different time moments. With a view to solve this problem combined method has been proposed. It contains boundary element method for description of field in surrounding air medium with inductor and also finite difference method for solving of the problem in molten metal. On the second step of the investigation with the help of obtained distribution of electrodynamic forces problem for acceleration of the melt has been solved. It is determined the optimal relation for pulse duration (in the case of single pulse), when melt velocity reaches its maximum value. Besides, it is shown that magnetic field may be used with the purpose of effect on crystallization zone through shell of solidified metal.

The metal-non-metal transition and the static and dynamic structure factor of expanded liquid alkali metals

Abstract: This paper reviews neutron scattering experiments on the static and dynamic structure factor of expanded liquid alkali metals from the melting point up to their critical point. Near the critical point, the change from a liquid metal to a non-metal takes place, which implies that the interatomic forces must exhibit drastic changes when the critical point is approached. Characteristic changes of the microscopic structure of the expanded liquid alkali metals have been observed. They expand non-uniformly and the dominant effect on the properties of the expanded liquids derives from a reduced mean coordination number and not from a drastic change of the interparticle distance. Measurements of the coherent dynamic structure factor S(Q, omega ) of expanded liquid rubidium reveal that up to about three times the critical density, the collective ion-ion dynamics is still controlled by the 'electron sea' of the expanded liquid metal. At lower densities of about twice the critical density, however, a drastic change of shape of S(Q, omega ) is observed, which might be due to the presence of paired units in the expanded liquid.

Electrical switches and sensors which use a non-toxic liquid metal composition

Abstract: Liquid gallium or gallium alloy (10) is utilized as the conductive fluid in a switch or sensor housing (12). In order to prevent wetting of the interior walls of the switch or sensor housing (12), the liquid gallium or gallium alloy (10) is either free of metal oxides or has only very low quantities of metal oxides. The gallium or gallium alloy (10) may be kept free of oxides by treating it with an acid, a base or a reducing agent and may be prevented from forming oxides during and after dispensing by removing air from the switch or sensor housing (12). An inert gas, such as argon, helium or hydrogen may fill the remainder of the housing (12) after the gallium or gallium alloy (10) has been dispensed. The gallium alloy may comprise indium, tin and/or bismuth.

Measurements of bubble plume behaviour and flow velocity in gas stirred liquid Wood's metal with an eccentric nozzle position

Abstract: The distribution of gas fraction and the flow field of gas-stirred liquid metal in steel ladles at eccentric injection of the stirring gas through the bottom of the vessel were measured in melts of 437 kg liquid Wood's metal. The melts had a temperature of 100° C. The bath height was 37 cm and the vessel diameter 40 cm. The blowing nozzle was positioned at half of the vessel radius. Gas flow rates were between 100 and 800 cm 3 (STP)/s. The gas fractions were measured by electrical resistance probes. The flow velocity of the liquid metal was determined by magnet-probes. The gas fraction and the velocity distribution in the plume were found to have a Gaussian shape. The cross-section of the plume is ellipsoid, as the plume width in the direction of the radius was a little smaller than the width in the direction perpendicular to it

Natural convection in an aluminum ingot: A mathematical model

Abstract: Strong buoyancy-driven flows are known to occur in the liquid metal pool of an aluminum ingot caster. These flows have a significant influence on the metallurgical structure of the ingot, largely through the redistribution of heat, fragmented dendrites, and segregated material within the pool. In this paper, we have developed a simple, analytical model of this process which predicts the distribution of temperature and velocity throughout the liquid metal pool. We demonstrate that the flow field can be separated into a relatively quiescent, stratified core bounded by thermally driven wall jets. The flows in the two regions then are matched through a global continuity equation, and the wall jets are handled using a momentum-integral technique. The result is a pair of coupled, nonlinear, ordinary differential equations. These equations are solved for two particular cases: one where the feed of liquid metal into the top of the pool is ignored and one where it is taken to be uniform over the top surface. Finally, our model predictions are compared with numerical experiments performed using a finite-difference code. The comparison is found to be satisfactory.

Assessment of alkali metal coolants for the ITER blanket

Abstract: The blanket system is one of the most important components of a fusion reactor becuase it has a major impact on both the economics and safety of fusion energy. The primary functions of the blanket in a deuterium-tritium-fueled fusion reactor are to convert the fusion energy into sensible heat and to breed tritium for the fuel cycle. The Blanket Comparison and Selection Study, conducted earlier, described the overall comparative performance of various blanket concepts, including liquid metal, molten salt, water, and helium. This paper discusses the International Thermonuclear Experimental Reactor requirements for a self-cooled blanket that uses liquid Li and for indirectly cooled blankets that use other alkali metals such as NaK. The paper addresses the thermodynamics of interactions between the liquid metals (e.g. Li and NaK) and structural materials (e.g. V-base alloys), together with associated corrosion and compatibility issues. Available experimental data are used to assess the long-term performance of the first wall in a liquid metal environment. Other key issues include development of electrically insulating coatings for the first-wall structural material to minimize magnetohydrodynamic (MHD) pressure drop, and tritium permeation and inventory in self-cooled and indirectly cooled blankets. Acceptable types of coating (based on their chemical compatibility and physical properties) are identified, and surface modifications to achieve these coatings on the first wall are discussed. The assessment examines the extent of our knowledge on the performance of structural materials in liquid metals and identifies needed research and development in several areas to establish performance envelopes for the first wall in a liquid metal environment.

Modelling of temperature losses in liquid metal during casting formation in expendable pattern casting process

Abstract: A finite difference model has been developed to study the effects of polymer degradation on the temperature of the liquid metal during the formation of the casting in the expendable pattern casting process. The model has been used to estimate the endothermic losses in the liquid metal during the mould filling process. The calculations have been conducted for pure aluminium and a commercial aluminium alloy. The results indicate that the temperature of the metal front decreases continuously during the formation of the casting. The degradation of the polymer establishes thermal gradients in the bulk of the casting of the order of 2–2·5 K cm−1. Thermal gradients as high as 50 K cm−1 may be achieved in a zone near the metal front. The heat transfer coefficient at the metal/mould interface has been estimated to be 420 Wm−2 K−1. The model suggests that the thickness of the gas layer at the metal front is negligibly small. The model confirms the experimental observation that a large fraction of the polym...

Fabrication of Metal Matrix Composite by Infiltration Process-Part 1: Modeling of Hydrodynamic and Thermal Behavior

Abstract: Modeling of hydrodynamic and thermal behavior during fabrication of metal matrix composites by infiltration process is presented. In terms of this model, the governing equations which describe the hydrodynamic and thermal behaviour of a liquid metal squeezed through a column of ceramic particles are solved. As a result, the time required for the liquid metal to penetrate completely throughout the column and the transient temperature distribution within the column are obtained. Also for a complete squeezing process, without freezing of the liquid metal at any location, the model is able to determine the initial melt superheat. The required melt superheat, for complete squeezing, is given as a function of the imposed pressure. It is found that increasing the imposed pressure will reduce the required superheat of the melt.

Methods to combat liquid metal embrittlement in cryogenic aluminum heat exchangers

Abstract: Liquid metal embrittlement (LME) is a rare but potentially catastrophic failure mechanism for chemical process equipment. Aluminum heat exchangers that process natural gas liquids are particularly at risk due to mercury contamination in natural gas feedstocks. Mechanisms of liquid metal attack peculiar to the Al/Hg system include amalgamation, amalgam corrosion, LME and intergranular attack that is preferential to weldments. The paper reports the results of a program directed at prevention and remediation of liquid metal attack of cryogenic aluminum heat exchangers. The specific topics discussed are (1) detection of liquid metal embrittlement using acoustic emission techniques (2) a chemical process to remove mercury from contaminated equipment (3) surface treatment methods to prevent mercury attack of equipment exposed to mercury (4) methods to assess the condition of the oxide in aluminum equipment. In general, corrosion and cracking of aluminum can be mitigated by several engineering approaches. Metallurgical selection of nonsusceptible alloys, choice of proper welding procedures and surface treatments to strengthen the oxide can be utilized when new equipment is fabricated. For contaminated equipment, selective oxidation and complexation of mercury can be utilized to prevent mercury attack and to remove existing amalgams, LME can be detected using AE to assist decisionmore » making for critical components handling liquefied natural gas. Surface condition also can be assessed using capacitance techniques to further aid decisions regarding remediation.« less

Double-duct liquid metal magnetohydrodynamic engine

Abstract: An internal combustion, liquid metal (LM) magnetohydrodynamic (MHD) engine and an alternating current (AC) magnetohydrodynamic generator, are used in combination to provide useful AC electric energy output. The engine design has four pistons and a double duct configuration, with each duct containing sodium potassium liquid metal confined between free pistons located at either end of the duct. The liquid metal is forced to flow back and forth in the duct by the movement of the pistons, which are alternatively driven by an internal combustion process. In the MHD generator, the two LM-MHD ducts pass in close proximity through a Hartmann duct with output transformer. AC power is produced by operating the engine with the liquid metal in the two generator ducts always flowing in counter directions. The amount of liquid metal maintained in the ducts may be varied. This provides a variable stroke length for the pistons. The engine/generator provides variable AC power at variable frequencies that correspond to the power demands of the vehicular propulsion. Also the engine should maintain nearly constant efficiency throughout the range of power usage. Automobiles and trucks could be powered by the invention, with no transmission or power converter devices being required.

MHD pressure drop in ducts with imperfectly insulating coatings

Abstract: Liquid metal cooled blankets in fusion tokamak`s are feasible only with electrically insulating coatings at the coolant channel walls. The requirements of such coatings are investigated and a simple analytical model is developed to determine the influence of imperfections in the coatings on the magneto-hydrodynamic pressure drop. This model is compared with the results of a 3D-MHD code based on the core flow approach. Both methods are in good agreement as long as the imperfections do not increase the pressure drop by more than 20%. The analytical model over-estimates the pressure drop for values larger than 20%. The importance of self-healing of coatings in case of cracking or flaking is quantified and an equation for the equilibrium conditions between the generation of imperfection and the healing of such spots is provided.

Startup performance of a liquid-metal heat pipe in near-vacuum and gas-loaded modes

Abstract: In liquid-metal heat pipes, a calculated amount of inert gas is filled as one of the safest means to start them from a frozen state. In the present study, an arterial-type sodium heat pipe with a long transport section has been tested for startup performance in both vacuum and gas-filled modes

Liquid metal surface tension measurements: a kinetic-fluodynamic model of surface oxygen availability

Abstract: A kinetic and fluodynamic description of processes that may take place near the surface of some liquid metals in the presence of a gas flow containing definite oxygen amounts is given, with a particular regard to the thermodynamic properties of the metal-oxygen system and to the geometry of the experimental set-up. Diagrams have been obtained from which the following items of information are simultaneously available: (1) the range of P02 and T in which the reaction considered is thermodynamically possible; (2) the accessibility of oxygen to the liquid metal surface, and the thermodynamic-kinetic conditions for which this surface can be considered oxygen free. Therefore, the treatment presented here and applied to many cases of technological interest allows us to define (a) the physical and chemical equilibrium conditions of a liquid metal surface in the presence of oxygen diluted in an inert gas carrier, under total pressures ranging from about 10−4 to 0.1 MPa (10−3−1 m), and (b) the kinetic and fluodynamic characteristics of the process through which the quilibrium conditions are reached, the geometry of the experimental set-up having been given.

Embrittlement of nanocrystalline nickel by liquid metals

Abstract: Metallographic and fractographic tests of liquid metal embrittlement are performed for nanocrystalline Ni-Hg systems. It is shown that the behaviour of nanocrystalline nickel under these conditions is close to that of ordinary polycrystalline materials. The presence of a stage of subcritical crack growth is demonstrated. As nanocrystalline grains have none of their own intrinsic dislocations, it is assumed that subcritical crack growth in liquid metal environment can be realized through the mechanism of dissolution of atoms from the crack tip. This dissolution-condensation model of liquid metal embrittlement, developed for polycrystals, can also be applied to nanocrystals.

Effective Interatomic Interactions in Liquid Metals

Abstract: Some liquid metals can be regarded as a binary mixture of ions and electrons interacting via binary interparticle interactions with each other. It is shown exactly on the basis of the density-functional method that a liquid metal can be taken as a quasi one-component system only via a pairwise interatomic interaction (without a many-body force) to obtain the radial distribution function, provided that a liquid metal can be thought of as an ion-electron mixture with binary interactions.