Showing papers on "Liquid metal published in 2007"

Liquid metal cooling in thermal management of computer chips

Abstract: With the rapid improvement of computer performance, tremendous heat generation in the chip becomes a major serious concern for thermal management. Meanwhile, CPU chips are becoming smaller and smaller with almost no room for the heat to escape. The total power-dissipation levels now reside on the order of 100 W with a peak power density of 400–500 W/cm2, and are still steadily climbing. As a result, it is extremely hard to attain higher performance and reliability. Because the conventional conduction and forcedair convection techniques are becoming incapable in providing adequate cooling for sophisticated electronic systems, new solutions such as liquid cooling, thermoelectric cooling, heat pipes, vapor chambers, etc. are being studied. Recently, it was realized that using a liquid metal or its alloys with a low melting point as coolant could significantly lower the chip temperature. This new generation heat transfer enhancement method raised many important fundamentals and practical issues to be solved. To accommodate to the coming endeavor in this area, this paper is dedicated to presenting an overall review on chip cooling using liquid metals or their alloys as coolant. Much more attention will be paid to the thermal properties of liquid metals with low melting points or their alloys and their potential applications in the chip cooling. Meanwhile, principles of several typical pumping methods such as mechanical, electromagnetic or peristaltic pumps will be illustrated. Some new advancement in making a liquid metal cooling device will be discussed. The liquid metal cooling is expected to open a new world for computer chip cooling because of its evident merits over traditional coolant.

Heat-driven liquid metal cooling device for the thermal management of a computer chip

Abstract: The tremendous heat generated in a computer chip or very large scale integrated circuit raises many challenging issues to be solved. Recently, liquid metal with a low melting point was established as the most conductive coolant for efficiently cooling the computer chip. Here, by making full use of the double merits of the liquid metal, i.e. superior heat transfer performance and electromagnetically drivable ability, we demonstrate for the first time the liquid-cooling concept for the thermal management of a computer chip using waste heat to power the thermoelectric generator (TEG) and thus the flow of the liquid metal. Such a device consumes no external net energy, which warrants it a self-supporting and completely silent liquid-cooling module. Experiments on devices driven by one or two stage TEGs indicate that a dramatic temperature drop on the simulating chip has been realized without the aid of any fans. The higher the heat load, the larger will be the temperature decrease caused by the cooling device. Further, the two TEGs will generate a larger current if a copper plate is sandwiched between them to enhance heat dissipation there. This new method is expected to be significant in future thermal management of a desk or notebook computer, where both efficient cooling and extremely low energy consumption are of major concern.

Electronic and structural transitions in dense liquid sodium

Abstract: It has recently been shown that, when high pressures are applied, crystals of lithium and sodium undergo a sequence of phase transitions — including (for sodium) a striking and as yet unexplained pressure-induced drop in the melting temperature. Jean-Yves Raty et al. have now identified the cause of this unusual melting behaviour: it emerges because liquid sodium undergoes a series of transitions similar to those seen in the solid state, but at much lower pressures. Intriguingly, one of these transitions is driven by the opening of a 'pseudogap' in the electronic density of states, the first time such an effect has been seen in a liquid metal. When high pressures are applied, crystals of lithium and sodium undergo a sequence of phase transitions, including a striking pressure-induced drop in the melting temperature. The cause of the unusual melting behaviour has now been identified: it emerges because liquid sodium undergoes a series of transitions similar to those seen in the solid state, but at much lower pressures. One of these transitions is driven by the opening of a 'pseudogap' in the electronic density of states. At ambient conditions, the light alkali metals are free-electron-like crystals with a highly symmetric structure. However, they were found recently to exhibit unexpected complexity under pressure1,2,3,4,5,6. It was predicted from theory1,2—and later confirmed by experiment3,4,5—that lithium and sodium undergo a sequence of symmetry-breaking transitions, driven by a Peierls mechanism, at high pressures. Measurements of the sodium melting curve6 have subsequently revealed an unprecedented (and still unexplained) pressure-induced drop in melting temperature from 1,000 K at 30 GPa down to room temperature at 120 GPa. Here we report results from ab initio calculations that explain the unusual melting behaviour in dense sodium. We show that molten sodium undergoes a series of pressure-induced structural and electronic transitions, analogous to those observed in solid sodium but commencing at much lower pressure in the presence of liquid disorder. As pressure is increased, liquid sodium initially evolves by assuming a more compact local structure. However, a transition to a lower-coordinated liquid takes place at a pressure of around 65 GPa, accompanied by a threefold drop in electrical conductivity. This transition is driven by the opening of a pseudogap, at the Fermi level, in the electronic density of states—an effect that has not hitherto been observed in a liquid metal. The lower-coordinated liquid emerges at high temperatures and above the stability region of a close-packed free-electron-like metal. We predict that similar exotic behaviour is possible in other materials as well.

Efficient Melt Stirring Using Pulse Sequences of a Rotating Magnetic Field: Part I. Flow Field in a Liquid Metal Column

Abstract: The use of a pulsed, rotating magnetic field (RMF) is presented as an auspicious method for obtaining an intensive stirring and mixing in a pool of liquid metal; the RMF pulses within a sequence have been applied with a constant or alternating direction. The resulting flow structure in a cylindrical liquid metal column has been explored by numerical simulations and by model experiments, using the ternary alloy GaInSn. Ultrasonic Doppler velocimetry (UDV) has been used to determine profiles of the vertical velocity. Both the numerical results and the velocity measurements demonstrate the capability of the proposed stirring regimes for overcoming the limited mixing character of conventional rotary stirring. The application of a time-modulated RMF offers considerable potential for providing an optimal flow pattern in a solidifying melt, for reasons of a well-aimed modification of casting properties.

Comparison of different theoretical models to experimental data on viscosity of binary liquid alloys

Abstract: Six different theoretical equations are compared in the present paper with experimental data, measured for 28 binary liquid metallic systems. General conclusions are drawn on the ability of the different theoretical models to describe the concentration and temperature dependence of the viscosity of liquid alloys. A new equation is derived, being able to predict the viscosity in multicomponents alloy even if the viscosities of the pure components are not known.

Submerged gas jet into a liquid bath : A review

Abstract: Gas-liquid jet reactors are widely used in commercial applications such as condensing jets for direct contact feedwater heaters and steam jet pumps, because of their efficient heat- and mass-transfer characteristics. These are also used for the blowdown of primary nuclear boiler systems into a water bath, without releasing fissionable materials into the atmosphere. Reacting jets are of major interest in metal processing and thermal energy sources that involve submerged injection of an oxidizer into a liquid metal bath. The design of gas-liquid jet reactors is strongly dependent on the plume dimensions and the flow pattern in the liquid phase. In the present review paper, a critical analysis of the published literature on the fluid dynamics and heat transfer for gas-liquid jet reactors has been performed. The analysis has been extended for the empirical, semiempirical, and analytical attempts for the correlations of experimental observations. The published works on the computational fluid dynamics (CFD) simulations have also been critically analyzed. A comprehensive discussion has been presented and an attempt has been made to arrive at a coherent theme that clearly describes the present status of the published literature. Furthermore, recommendations have been made that are expected to be useful for the design engineers as well as researchers, to improve the reliability in the design of this important class of reactors.

Liquid metal/ceramic interactions in the (Cu, Ag, Au)/ZrB2 systems

Abstract: Wetting and spreading experiments on ZrB2 in contact with liquid Cu, Ag and Au have been performed by the sessile drop technique under a vacuum. The wetting and spreading characteristics and the interfacial reactions are discussed as a function of time and of the metal involved. The interfacial morphologies, analysed by optical microscopy, SEM and EDS show the presence of regular interfaces without macroscopic reaction layers. Gold, to a very large extent and copper are shown to give rise to extensive penetration along grain-boundaries, whereas silver neither wets nor penetrates. Interfacial diffusion/dissolution is taken into account and the consequent changes in liquid metal surface tension and wetting behaviours have been evaluated by means of thermodynamic calculations. Moreover, interfacial energetics at the atomistic level has been investigated by means of pseudopotential-based Density Functional Theory (DFT) technique. It is shown how the calculation of the ideal work of separation on the specific transition metal borides-molten metal systems can be used to interpret the wetting behaviour. Moreover, the dependence of the adhesion behaviour on the electronic structure at the interface and on the interface epitaxy and composition is also briefly discussed.

Super flexible sensor skin using liquid metal as interconnect

Abstract: Robust, flexible sensor skins have long been expected in robotic control. However, most flexible sensor skins are simply fabricated on flexible substrates with the sensor elements and electrical interconnects made from solid materials, which limits the flexibility of sensor skins. Here, we successfully incorporated liquid metal as interconnect to develop a super flexible sensor skin, which senses temperature and force simultaneously. The sensing element is PDMS elastomer mixed with 10% weight ratio multi-walled carbon nanotubes (MWNT). A eutectic liquid metal alloy (Galinstan: 68.5% Ga, 21.5% In, 10% Sn) material filled in microchannels as electrical interconnects. Thus, this skin can be bent dramatically without worrying about failure, which is a big issue for solid metal interconnects. The temperature coefficient of resistance (TCR) reaches 0.4%/degC, comparable to commercial resistance temperature detectors. The resistance change versus applied force was around 0.3%/KG.

Non-Toxic Liquid-Metal 2-100 GHz MEMS Switch

Abstract: In this paper, the first wide-band MEMS capacitive switch using non-toxic liquid metal, Galinstan, is reported. Controlled movement of Galinstan in a micro-channel alters the impedance of a coplanar waveguide (CPW) line from 50 Omega (off-state) to an effective RF short circuit (on-state). The RF short circuit in particular is achieved when a slug of Galinstan capacitively connects the center conductor with the ground planes of the CPW line. Galinstan is reliably manipulated by surrounding it with Teflon solution. Because of Teflon, no residual liquid metal is observed when Galinstan moves. In addition, the Teflon solution has insignificant RF loss and therefore does not adversely affect the switch loss in its off-state even up to 100 GHz. The insertion loss of the switch is measured at 0.2, 0.7 and 1.3 dB at 20, 40 and 100 GHz respectively and is mainly due to the 1500 mum long transmission line. The on-state shunt capacitance is measured to be 4 pF which results in an on-state isolation of greater than 20 dB from 20 to 100 GHz.

Microrelays With Bidirectional Electrothermal Electromagnetic Actuators and Liquid Metal Wetted Contacts

Abstract: Microrelays with liquid metal wetted contacts have been demonstrated using bidirectional electrothermal electromagnetic actuators These relays were fabricated with the Metal MUMPs foundry process, which has a 20-mum-thick nickel structural layer The operating voltage is under 05 V The measured breakdown voltage and off-state resistance are greater than 200 V and 100 MOmega, respectively, and the gold-to-gold contact resistance is around 03 Omega When the contacts are wetted with liquid gallium alloy (melting point at -20degC), the measured contact resistance can be as low as 0015 Omega As such, these bidirectional relays could have potential applications in high-power switching systems with low contact resistance using liquid metal wetted contacts

The Effects of Surface Roughness and Metal Temperature on the Heat-Transfer Coefficient at the Metal Mold Interface

Abstract: This article focused on the effects of surface roughness and temperature on the heat-transfer coefficient at the metal mold interface. The experimental work was carried out in a unique and versatile apparatus, which was instrumented with two types of sensors, thermocouples, and linear variable differential transformers (LVDTs). The monitoring of the two types of sensors was carried out simultaneously during solidification. The concurrent use of two independent sensors provided mutually supportive data, thereby strengthening the validity of the interpretations that were made. With this type of instrumentation, it was possible to measure temperature profiles in mold and casting, as well as the air gap at the metal mold interface. Commercial purity aluminum was cast against steel and high carbon iron molds. Each type of mold had a unique surface roughness value. Inverse heat-transfer analysis was used to estimate the heat-transfer coefficient and the heat flux at the metal mold interface. A significant drop in the heat-transfer coefficient was registered, which coincided with the time period of the air gap formation, detected by the LVDT. An equation of the form \(h\, = \,\frac{1} {{b^{\ast}A + c}}\, + \,d\) was found to provide excellent correlation between the heat-transfer coefficient and air gap size. In general, an increase in mold surface roughness results in a decrease in the heat-transfer coefficient at the metal mold interface. On the other hand, a rise in liquid metal temperature results in a higher heat-transfer coefficient.

Assessment of correlations for heat transfer to the coolant for heavy liquid metal cooled core designs

Abstract: In the development of the accelerator driven systems XT-ADS and EFIT lead-bismuth eutectic alloy (LBE) and lead are foreseen as coolant respectively. For calculation of the heat transfer from the fuel rod surfaces to the coolant correlations are necessary. Existing correlations for triangular and square fuel pin arrangements are reviewed with respect to their experimental qualification. Effects on the heat transfer in reactor application are addressed, which could alter the correlations due to deviating boundary conditions. These are the influence of spacers and consequences due to the axial power profile.

Physical Chemistry of Corrosion and Oxygen Control in Liquid Lead and Lead-Bismuth Eutectic

Abstract: Corrosion of steel in liquid lead (Pb) and lead-bismuth eutectic (LBE) is an important factor when applying these materials as a process medium. At low oxygen content of the liquid-metal phase, the degradation results mainly from the dissolution of the steel constituents, which may significantly decrease in the presence of a continuous scale of oxides of the steel constituents on the steel surface. In order to facilitate the formation of such a scale, the oxygen content of the liquid metal has to be controlled. Therefore, a method of measuring the oxygen content must be available. This report addresses the thermodynamic fundamentals of steel corrosion in oxygen-containing liquid metals and provides the data on chemical and physical properties which is required for the determination of favourable conditions with respect to the oxygen content and the numerical analysis of the dissolution of the primary steel constituents in oxygen-containing liquid Pb and LBE. Furthermore, the measurement of the oxygen content with electrochemical oxygen sensors and the evaluation of the sensor output is discussed.

Molecular dynamics simulation of Ga penetration along grain boundaries in Al: a dislocation climb mechanism.

Abstract: Many systems where a liquid metal is in contact with a polycrystalline solid exhibit deep liquid grooves where the grain boundary meets the solid-liquid interface. For example, liquid Ga quickly penetrates deep into grain boundaries in Al, leading to intergranular fracture under very small stresses. We report on a series of molecular dynamics simulations of liquid Ga in contact with an Al bicrystal. We identify the mechanism for liquid metal embrittlement, develop a new model for it, and show that is in excellent agreement with both simulation and experimental data.

Liquid metals for nuclear applications

Abstract: Nuclear applications of liquid metals concern waste transmuters and liquid metal cooled fast reactors of Generation IV. One section of this paper is devoted to a short review of the motivations for liquid metals as reactor coolant or spallation target material and to historic aspects. The next two sections are dedicated to the neutron and physical properties of liquid metals, with special emphasis on sodium, lead and lead–bismuth eutectic, their respective advantages and drawbacks as reactor coolants. The question of the structure of liquid metals in relation with the liquid metal coolant technology is briefly addressed. The last section concerns the compatibility of structural materials with sodium, lead and lead–bismuth eutectic, with attention being paid to the impurities control in the different cases. We conclude briefly.

Temperature Dependence of the Velocity of Sound in Liquid Metals of Group XIV

Abstract: The temperature dependences of the velocity of sound in liquid Pb, Sn, Ge, and Si have been measured by means of the pulse transmission technique over temperature ranges of 610–1078 K, 608–1463 K, 1215–1443 K, and 1723–1888 K, respectively. In both liquid Pb and Sn, the velocities of sound decrease linearly with increasing temperature, which is the same temperature dependence as shown in many other liquid metals. On the other hand, the velocities of sound in liquid Ge and Si exhibit anomalous temperature dependences. In Ge, the velocity of sound has a distinct maximum around 1280 K and decreases linearly at higher temperatures. In Si, the velocity of sound increases monotonically with increasing temperature in the temperature range investigated. It is considered that these results predict that the coordination numbers of liquid Ge and Si increase with increasing temperature.

Improved signal stability from a laser vaporization source with a liquid metal target

Abstract: The translating and rotating rod or disk of a conventional laser vaporization cluster source is replaced by a liquid metal target. The self-regenerating liquid surface prevents cavities from being bored into the sample by laser ablation. The laser beam strikes a near pristine surface with each pulse, resulting in signals with much better short and long term stabilities. While this approach cannot be used for refractory metals such as tungsten and molybdenum, it is ideal for studies of bimetallic clusters, which can easily be prepared by laser vaporization of a liquid metal alloy.

Research and development of radiation resistant ultrasonic sensors for quasi- image forming systems in a liquid lead-bismuth

Abstract: The problems of the development of high-temperature radiation resistant ultrasonic sensors operating in a liquid lead-bismuth alloy are analyzed. Experimental diffusion bonded bismuth titanate sensors for operation up to 450 °C were developed. For acoustical coupling with a liquid metal the sensor protector is polished or coated by a diamond like carbon layer. The developed sensors survived high irradiation doses and experienced only 4 % decrease of the transfer coefficient after gamma irradiation by 22 MGy dose. Experiments in a liquid lead-bismuth were provided, including sensor long term wettability tests, determination of ultrasound losses and measurement of the ultrasound velocity temperature dependence.

Giant Metal Compression at Liquid-Solid (Pb-Si, In-Si) Schottky Junctions

Abstract: Using a high-energy x-ray transmission-reflection scheme we have studied the density profile of solid-liquid Schottky contacts close to the interface. We found a massive disturbance of the electronic system on the liquid metal side at different interfaces with pronounced density anomalies on a new length scale. The liquid metal at the interface forms a strongly compressed layer followed by a density depleted layer. The experimental evidence points to a charge transfer phenomenon in the metallic system. Control experiments performed at a metal-insulator interface confirm this picture.

One-Dimensional Analysis of Thermal Stratification in AHTR and SFR Coolant Pools

Abstract: Thermal stratification phenomena are very common in pool type reactor systems, such as the liquid-salt cooled Advanced High Temperature Reactor (AHTR) and liquid-metal cooled fast reactor systems such as the Sodium Fast Reactor (SFR). It is important to accurately predict the temperature and density distributions both for design optimation and accident analysis. Current major reactor system analysis codes such as RELAP5 (for LWR’s, and recently extended to analyze high temperature reactors), TRAC (for LWR’s), and SASSYS (for liquid metal fast reactors) only provide lumped-volume based models which can only give very approximate results and can only handle simple cases with one mixing source. While 2-D or 3-D CFD methods can be used to analyze simple configurations, these methods require very fine grid resolution to resolve thin substructures such as jets and wall boundaries, yet such fine grid resolution is difficult or impossible to provide for studying the reactor response to transients due to computational expense. Therefore, new methods are needed to support design optimization and safety analysis of Generation IV pool type reactor systems. Previous scaling has shown that stratified mixing processes in large stably stratified enclosures can be described using one-dimensional differential equations, with the vertical transport by free and wall jets modeled using standard integral techniques. This allows very large reductions in computational effort compared to three-dimensional numerical modeling of turbulent mixing in large enclosures. The BMIX++ (Berkeley mechanistic MIXing code in C++) code was originally developed at UC Berkeley to implement such ideas. This code solves mixing and heat transfer problems in stably stratified enclosures. The code uses a Lagrangian approach to solve 1-D transient governing equations for the ambient fluid and uses analytical or 1-D integral models to compute substructures. By including liquid salt properties, BMIX++ code is extended to analyze liquid salt pool systems in the current AHTR design, to provide an example of its application. Similar analysis is possible for liquid-metal cooled reactors. The current AHTR baseline design uses a large buffer salt tank to provide more thermal inertial and safety margin. Reactor vessel, intermediate heat exchangers, pool reactor auxiliary cooling system heat exchangers (PHX), and direct reactor auxiliary cooling system heat exchangers (DHX) are all immerged in the buffer salt pool. These structures provide major driving sources for vertical mixing and thermal stratification. Predication of the temperature distribution within the buffer salt tank directly affects the major safety systems design, such as the PHX and DHX, safety analysis results, and structure thermal stresses analysis. The BMIX++ code is used to predict mixing and thermal stratification in this pool system. This example shows the potential of 1-D analysis methods and BMIX++ to be included in system analysis codes for pool type of Gen-IV reactor systems.

Nano metal fluid with high heat-transfer performance

Abstract: This invention provides a high heat transfer performance liquid nano-metal. It relates to cooling fluid working medium, and especially it can be used under high rush density condition which need high intensity cooling fluid working medium for heat exchanging and cooling, such as computer array and reactor. The solvent of this invention is liquid metal, and the soluble of this invention is nanometer particle. This invention solve the problem of high price of present metal liquid cooling working medium and the limited performance of common metal liquid, leaking out easily taken place using common liquid and easy forming sediment of present nanometer cooling agent.