Containerless Processing in Space—Thermophysical Property Measurements Using Electromagnetic Levitation

Electromagnetic levitation is a novel tool for measuring thermophysical properties of high-temperature metallic melts. Contamination by a crucible is avoided, and undercooling becomes possible. By exploiting the microgravity environment of an orbiting spacecraft, the positioning fields can be further reduced and undesired side effects of these fields can be minimized. After two successful Spacelab flights of the electromagnetic levitation facility TEMPUS, an advanced electromagnetic levitation facility is presently being studied for accommodation on the International Space Station, ISS. Due to the permanent nature of the ISS, an operational concept must be defined which allows the exchange of consumables without exchanging the entire facilty. This is accomplished by a modular design, which is presented. For all experiments, like measurement of specific heat, of surface tension and viscosity, of thermal expansion, and of electrical conductivity, noncontact diagnostic tools must be either improved or developed. Such tools are, for example, pyrometry, videography (high-speed and high-resolution), and inductive measurements. This paper summarizes the scientific results obtained so far and deduces some lessons learned that will be incorporated into the new design and will lead to both new results and a higher precision of the data.     

Electrical Resistivity of Undercooled Liquid Cu-Ni Alloys

Measured values for the electrical resistivity of undercooled liquid Cu-Ni alloys of different compositions are presented. The experiments were performed in a facility that combines the containerless positioning method of electromagnetic levitation with the contactless inductive resistivity measurement technique. For high nickel concentrations, i.e., for the liquid Cu₂₀Ni₈₀ and Cu₄₀Ni₆₀ alloys, the electrical resistivity shows, as well as for pure nickel and pure copper, the typical linear temperature dependence in the whole range from above to below the liquidus temperature. A significant deviation from the linear behavior occurs for liquid Cu₆₀Ni₄₀ and, less distinct, also for liquid Cu₈₀Ni₂₀. This is explained by a formation of nickel associates in the melt that influence the scattering cross section of the conduction electrons.     

Measurement Method to Evaluate the Practical Levitation Force of Onboard Bulk Superconductor in the High-Temperature Superconducting Maglev Vehicle System

As the basic parameter in the design of high-temperature superconducting (HTS) magnet levitation (maglev) vehicle system, the levitation force data are usually obtained by experiments, so a reliable measurement method is needed to know the practical levitation force of onboard bulk superconductor. Considering in the actual operation the vehicle will experience some small vertical or lateral movements, especially during the passenger going on or off the vehicle, the usual measurement method for levitation force, in which force with gap and force relaxation are measured, cannot be able to predict the levitation force change due to the vertical or lateral movements. So a measurement method is presented regarding effects of force with gap, relaxation, vertical and lateral movements. Compared with a former measurement method, the presented method may support more reliable levitation force data for the HTS maglev vehicle design.     

Inductive measurement of metallic cylindrical shells

The thickness of thin cylindrical copper shells of radiusaand thicknessD(D/a < 0.15)were measured by means of an inductive measurement. The samples were obtained by chemical reduction of thick copper pipes. The conductivity of the cylinders was measured by a standard four-terminal technique. The agreement between the value of thickness measured mechanically and the value obtained from inductive measurement is of the order of ±2 percent. Thicker brass shells were measured and these results compared with theory. The extension of the inductive measurement to cylindrical shells covering cylinders with a finite conductivity is also discussed.     

开孔金属泡沫的传热分析

主要从开孔金属泡沫微观组织的基本结构出发对开孔金属泡沫内的固体热传导、气体热传导和热辐射进行了分析,根据以上的分析利用能量方程和两热流法建立了开孔金属泡沫的传热模型,并利用试验对泡沫镍的有效导热系数进行了测量,泡沫镍的有效导热系数实验值验证了开孔金属泡沫传热模型的正确性.     

Electrical conductivity measurements in liquid metals by rotational technique

The rotational contactless inductive measurement technique has been developed to measure the electrical conductivity of liquid metals. This method is based on the phenomena when a conductor material rotates in a magnetic field, circulating eddy currents are induced and generate a damping torque proportional to the electrical resistivity of the material. The technique was tested to measure the conductivity of five conductors and one low melting composite (LMA-158).     

Electrical resistivity measurements on binary Al-15 wt-%In alloy

Abstract

A rotational contactless inductive measurement technique has been used to determine the electrical resistivity of an Al-15In (wt-%) binary alloy over a wide range of temperatures. It is shown that the electrical resistivity depends on the distribution of the indium within the aluminium matrix. The results can be considered as a first attempt to detect the onset of the sedimentation process, which occurs in alloys of this type, by measuring the electrical conductivity of immiscible alloys.     

Radiative heat exchange method for thermal conductivity measurement applying a perpendicular heat flow to a thin-plate sample: Principle and apparatus

To measure thermal conductivity of materials of low conductivity (0.1 to 1 W·m^–1·K^–1), a method using a specimen of small size (2×25×25 mm) has been developed. This method applies a well-defined, steady, and uniform heat flux perpendicular to the surface of a small plate sample of polymers or ceramics jointly by means of radiative heat exchange as well as by an areal heater on the sample surface and allows a reasonably rapid (5-min) measurement of thermal conductivity. This method of measuring conductivity is an absolute and direct measurement method which does not need any standard reference materials or information about heat capacity. The principle of the method has been demonstrated by constructing a measurement apparatus and measuring thermal conductivity of a few materials. The thermal conductivities of silicone rubber and Pyrex (Corning 7740) glass measured by the present method between 30 and 90°C are compared with recommended values.     

以物体表面温度推算变导热系数的测试原理及技术

提出了一种根据第三类边界条件下物体表面温度的测定值推算随温度线性变化的物体导热系数的测试原理和方法。利用设计的测试系统对几种材料的导热系数进行了测量和计算。结果表明，测试计算方法简单可行。为测定物体变导热系数提供了一个有效的方法。     

A procedure to study thermo- and electrophysical properties of materials

We describe a measurement procedure and the construction of an automatic measuring complex to study thermal conductivity by an absolute stationary method and also electrical conductivity and thermal EMF of materials in a temperature range from −60 to +4400 ° C. The use of a specialized microprocessor system to perform stationary measurements and to control parameter measurement processes in combination with highgrade measuring devices and equipment developed for this procedure enables high accuracy of measurements. Test studies performed on reference samples show that the thermal conductivity measurement error does not exceed 4 and 3% for electrical conductivity and thermal EMF, respectively. In the development of devices and equipment for this measuring complex, unconventional engineering, schematic, and programming solutions are implemented. The application of a microprocessor control system together with the software developed allows the measurements to be performed automatically.     

第三类边界条件下利用物体表面温度推算物体导热系数的实验技术

提出了一种根据第三类边界条件下物体瞬态温度场的变化规律，利用物体表面温度的实测值推算物体导热系数的快速测定方法。设计了一种可以在较高表面换热强度条件下进行测试的装置，导热系数的测定范围较宽。实验结果表明，测试方法简单，测试时间短。比较实用可靠。     

Electrical and thermal conductivity of A319 and A356 aluminum alloys

A rotational contactless inductive measurement technique has been used to measure the electrical resistivity of A319 and A356 aluminum alloys at both solid and liquid states. The method is based on the phenomena that when a conducting material rotates in a magnetic field, circulating eddy currents are induced and generate an opposing torque, which is proportional to the electrical conductivity of the material. The technique was checked and calibrated with pure aluminum where considerable electrical resistivity data exist in the literature. Wiedemann-Franz-Lorenz law was used to estimate the thermal conductivity of A319 and A356 aluminum alloys in liquid state.     

Thermophysical Properties of Undercooled Liquid Co80Pd20

The surface tension, viscosity, and electrical resistivity of liquid Co₈₀Pd₂₀were measured containerlessly for temperatures above and, especially, below the melting point. The first two quantities were measured with the help of the oscillating drop technique, the last one by an inductive method. The experiments have been performed under low gravity in the electromagnetic levitation facility TEMPUS during the MSL-1 Spacelab mission. This environment allowed us to measure for the first time the viscosity and electrical resistivity in the deeply undercooled state, where the Co₈₀Pd₂₀melt shows a magnetic ordering behavior. In this paper the measurement methods and results are presented.     

Simple measurement of the AC transport current loss for HTS conductors using an active power detection method

Reducing AC loss in a superconducting apparatus is one of the most important issues, and the precise measurement and estimation of AC losses are essential to reduce them. The four-terminal method is universally used as an electric measurement method of AC losses for superconducting tapes and wires. In this method, noise and inductive voltage superposed on the terminal voltage of the superconductor are eliminated by a lock-in amplifier and cancel coil, respectively, and then measurement of very small resistive voltage is achieved. However, using this conventional method, a plurality of measuring instruments and apparatuses are needed, and therefore the measuring system becomes complicated and much time is consumed in the calibration process. In this paper, we present a simple and precise measurement system based on an active power detection method, which is proposed as a quench detection method. The proposed system consists of a small number of instruments and apparatus and is less susceptible to noise. Its usefulness is verified by comparing the proposed method and the conventional four-terminal method in measuring the AC transport current loss of a Bi2223/Ag tape.     

Magnetic Forces Relaxation Step Change Characteristics of YBCO Bulk with Mechanical Impact Load over a NdFeB Guideway

Magnetic force relaxation of YBCO bulk above the NdFeB permanent magnet guideway (PMG) with impact load has been investigated. An experimental setup has been built using a single YBCO bulk and a symmetrical center NdFeB PMG. There are two experimental methods: the case of magnetic levitation force relaxation measuring perturbed with impact load in zero-field-cooling (ZFC); and the case of magnetic levitation and guidance force relaxation measuring synchronously perturbed with impact load in field-cooling (FC). The results show that there is magnetic levitation and guidance forces relaxation step change at the time of the impact load. Two times impact loads are applied for each method. The first step change range is much larger than the second one. The Bean critical model and Anderson–Kim theory are used to analyze it.     

磁浮列车磁场测量系统中运动控制平台的设计

磁浮列车气隙磁场的测量可以为列车电磁系统的设计和控制提供重要依据．本文对气隙测量系统中磁传感器运动控制平台的设计进行了详细介绍,阐述了运动控制平台的工作原理和光栅尺信号的处理方法．采用双计数器鉴相法消除了光栅尺抖动的影响,提高了传感器的定位精度．同时采用电流矢量恒幅旋转的细分方法实现了步进电机恒转矩均匀细分控制,提高了步进电机的分辨率和运行稳定性．所设计的运动控制平台的定位精度可以达到1μm．     

热探针法测定含湿土壤的导热系数

根据线热源瞬态导热模型,设计制作了用于测定含湿土壤导热系数的热探针,研究了加热功率、加热时间、探针壁厚对导热系数测定的影响。对不同含水量的土壤导热系数进行测定,得出纯土、河沙含水量～导热系数拟合关系式。结果表明,热探针法测定含湿土壤的导热系数具有便捷、准确的特点。     

Ambiguous temperature difference in aerodynamic levitation process: Modelling,solving and application

The aerodynamic levitation provides an efficient technique for the research on thermophysical properties and solidification behavior of refractory materials. However, there is a nonnegligible temperature differences across sample, causing unexpected uncertainty of measurement, such as, thermal expansivity and undercooling limit. We establish thermal filed model with properly simplified boundary condition, and derive quantitative expressions of this ambiguous temperature difference. Here we show that the temperature difference not only related to the average temperature, relative size and thermal conductivity of sample, but significantly influenced by the rotation pattern of sample. A huge temperature differences is almost inevitable when the sample with low thermal conductivity and high melting point is smelted in stationary suspension pattern, however, a drastically reduction of temperature difference can be fulfilled by simply making the sample rotation in up to down pattern. The thermal filed simulation was used to confirm the validity of these theoretical expressions. This work shed light on temperature difference in aerodynamic levitation. Based on this work, one can simply estimate the extent of temperature difference across the sample, and regulated that conveniently if needed, which benefit for novel material preparation and solidification mechanism study based on this technique.     

Aerodynamic Levitation and Inductive Heating – A New Concept for Structural Investigations of Undercooled Melts

The combined application of containerless techniques with X-ray diffraction and absorption at synchrotron sources as well as neutron diffraction enables structural investigations of high-melting-point and/or corrosive liquids above the melting point and in the undercooled state. A variety of containerless techniques are available including electromagnetic and aerodynamic levitation. In the framework of a bilateral project, a new hybrid system combining aerodynamic levitation with inductive heating is being developed. Advantages and concept of the setup are discussed. Different Helmholtz coils and cylindrical coils were used to heat levitated, solid samples. Melting and stable levitation in the liquid state were achieved for aluminum. The general problem of deformation of liquid samples by electromagnetic fields is discussed. Paper presented at the Seventh International Workshop on Subsecond Thermophysics, October 6–8, 2004, Orléans, France.