A Novel Instrument for the Measurement of the Thermal Conductivity of Molten Metals. Part I: Instrument’s Description

The paper reports the design and construction of a new instrument for the measurement of the thermal conductivity of molten metals and salts. The apparatus is based on the transient hot-wire technique, and it is intended for operation over a wide range of temperatures, from ambient up to 1200 K. The present experimental technique overcomes problems of convection and thermal radiation, and it is demonstrated that it operates in accord with a theoretical model. The uncertainty of the thermal conductivity results is estimated to be ±2% which is superior to that achieved in most earlier work.     

A Novel Instrument for the Measurement of the Thermal Conductivity of Molten Metals. Part II: Measurements

New measurements of the thermal conductivity of molten mercury, gallium, tin, and indium are reported up to 750 K. The measurements are performed in a novel transient hot-wire instrument described elsewhere. The present experimental technique overcomes problems of convection, and it is shown that it operates in an absolute way in accord with a theoretical model. The uncertainty of the thermal conductivity results is estimated to be ± 2%, which is superior to that achieved in most earlier work. The low uncertainty of the present experimental results has allowed us to test the only significant theory for the thermal conductivity of molten metals, which relates this property to the electrical conductivity. The pattern of results among the four metals indicates that further theoretical developments would be warranted.     

Thermal Conductivity of Molten Lead-Free Solders

The paper reports measurements of the thermal conductivity of a number of molten solders for the electronics industry that are part of a group of materials designed to be free of the toxic problems associated with lead-based solders. The measurements have been carried out with a transient hot-wire instrument originally designed for the measurement of the thermal conductivity of pure molten metals. In the application reported here the instrument has been used largely unchanged but an improved finite-element code has been used for the analysis of the raw data so as to yield the thermal conductivity of the molten solders. The measurements extend from the melting point of the solder up to 625 K. The uncertainty in the thermal conductivity measurements is estimated to be no larger than 3%.Paper presented at the Seventh Asian Thermophysical Properties Conference, August 23–28, 2004, Hefei and Huangshan, Anhui, P. R. China     

The thermal conductivity of the molten NaNO3-KNO3 eutectic between 525 and 590 K

Molten salts are one of the few remaining classes of fluids for which standardquality (±1% accuracy) data on thermal conductivity have not hitherto been available. We have therefore developed a new apparatus based on the transient hot-wire technique to obtain reference-quality measurements of the thermal conductivity of molten salts at high temperatures. Liquid metal-filled quartz capillaries served as insulated hot wires in our method, and in addition, a two-wire technique was used in order to obtain absolute values of the thermal conductivity. New data for the NaNO₃-KNO₃ eutectic between 525 and 590 K are reported in this paper and comparisons with other recent measurements are shown.     

The thermal conductivity of molten NaNO3 and KNO3

The thermal conductivity data for molten NaNO₃ and KNO₃ have been examined in order to propose recommended data sets for these two popular heat carriers and to establish the reference values above the temperature range covered by toluene and water. It is known that the measurement of the thermal conductivity of molten salts is very difficult, owing mainly to their corrosiveness and high melting temperatures, which introduce complications in apparatus design and significant systematic errors due to radiation and convection. However, some recent measurements seem to manifest more trustworthy values than obtained before. All available data have been collected and critically evaluated. The temperature range covered is 584 to 662 K for molten NaNO₃ and 662 to 712 K for molten KNO₃, with the confidence limits better than ± 5%.     

Measurements of the Thermal Conductivity of Molten Lead Using a New Transient Hot-Wire Sensor

The paper reports new measurements of the thermal conductivity of molten lead at temperatures from 600 to 750 K. The measurements have been carried out with an updated version of a modified transient hot-wire (THW) method, where the hot-wire sensor is embedded within an insulating substrate with a planar geometry. However, unlike previous sensors of the same type, the updated sensor works with the hot-wire divided into three thermally isolated parts. The operation of this sensor has been modeled theoretically using a finite-element (FE) analysis and has subsequently been confirmed by direct observation. The new sensor is demonstrated to have a higher sensitivity and a better signal-to-noise ratio than earlier sensors. Molten lead is used as the test fluid. It has the lowest thermal conductivity of any material we have yet studied. This allows us to probe the limits of our sensor system for the thermal conductivity of high-temperature melts. It is estimated that the uncertainty of the measurements is 3% over the temperature range studied. The results are used to examine the application of the Wiedemann–Franz (W-F) relationship.     

Experimental determination of the thermal diffusivity of molten alkali halides by the forced Rayleigh scattering method. II. Molten NaBr,KBr, RbBr,and CsBr

This is a companion to an earlier paper (on molten alkali metal chlorides) which gives experimental results for the thermal diffusivity of four molten alkali metal bromides: NaBr, KBr, RbBr, and CsBr. The measurements were performed with a forced Rayleigh scattering instrument at temperatures up to 1326 K. The overall uncertainty in the measured thermal diffusivity is estimated to be ±3 to ±11%, depending on the measured salts. The results converted to thermal conductivity show one of the smallest values among other earlier experimental data obtained mainly by the steady-state methods. It is also found that the temperature dependence of the thermal conductivity is weakly negative.     

Thermal conductivity of aqueous solutions of NaCl and KCI at high pressures

This paper presents new experimental measurements of the thermal conductivity of aqueous solutions of NaCl and KCl at high pressures. The measurements were made with a parallel-plate apparatus. The temperatures covered the range from 293 to 473 K at pressures up to 100 MPa and concentrations from 0.025 to 0.25 mass fraction of NaCl and KCl. The measurements included 6 isobars at pressures from 0.1 to 100 MPa at intervals of 20 MPa, 10 isotherms at temperatures from 293 to 473 K at intervals of 20 K, and 6 isopleths at concentrations from 0.025 to 0.25 mass fraction of NaCl and KCl at intervals of 0.05. The precision of the measurements was ±1.6%. The thermal conductivity obtained for NaCl + H₂O and KCl + H₂O was compared with data of other authors, with satisfactory agreement. The viability of the technique was confirmed and the essential features of a high-precision instrument were established.     

Experimental determination of the thermal conductivity of thin films

Two techniques have been developed to determine experimentally the thermal conductivity of thin solid films of thickness 500 Å or more at low and high temperatures. The first technique is a steady state and is suitable for measurements above room temperature. The method enables the thermal conductivity of eight film specimens to be measured simultaneously. The second technique is a transient one (an adaptation of Ioffe's method for bulk materials) and is suitable for measurements in the temperature range 100–260 K. The two techniques have been used to make measurements of thin films of copper and various crystalline and amorphous semiconductors. The values of the thermal conductivity for thick copper films by both techniques agree quite well with the bulk values.     

Microsecond Laser Polarimetry for Emissivity Measurements on Liquid Metals at High Temperatures—Application to Tantalum

The aim of this work was to determine accurate and reliable thermophysical properties of liquid tantalum from melting up to temperatures of 5000 K. Temperature measurements on pulse-heated liquid metal samples reported by different authors have always been performed under the assumption of a constant emissivity over the whole liquid range because of the lack of data for liquid metals. The uncertainty in temperature measurement is reduced in this work by the direct measurement of emissivity during the experiments. The emissivity measurements are performed by linking a laser polarimetry technique with the established method for performing high speed measurements on liquid tantalum samples at high temperatures during microsecond pulse-heating experiments. A set of improved thermophysical properties for liquid tantalum, such as temperature dependences of normal spectral emissivity at 684.5 nm, heat capacity, enthalpy, electrical resistivity, thermal diffusivity, and thermal conductivity, was obtained.     

Thermal Conductivity of Pure Noble Gases at Low Density from Ab Initio Prandtl Number

The experimental data reported in the literature after 2000 have been investigated for the viscosity and thermal conductivity of helium-4, neon, and argon at low density. The well-established values of thermal conductivity by transient hot-wire measurements are not reliable enough for noble gases in the low-pressure gas region. These facts motivate us to determine the thermal conductivity from accurate viscosity data and the ab initio Prandtl number, with an uncertainty of 0.25 % for temperatures ranging between 200 K and 700 K. The theoretical accuracy is superior to the accuracy of the best measurements. The calculated results are accurate enough to be applied as standard values for the thermal conductivity of helium-4, neon, and argon over the considered temperature range.     

Repeatability and Refinement of a Transient Hot-Wire Instrument for Measuring the Thermal Conductivity of High-Temperature Melts

The paper reports an assessment of the repeatability of a method for the measurement of the thermal conductivity of high temperature melts. The main goal is to demonstrate that a novel approach to the transient hot-wire technique can yield highly accurate results that are consistent with previous, independent measurements. The paper summarizes the modified transient hot-wire method, presents improvements in the finite-element analysis of its operation, and briefly discusses deviations from available analytical equations. The transient hot-wire instrument and experimental configuration are also described. Results from measurements on molten metals, in particular, tin and indium, in the temperature range from their melting points up to 750 K are presented. A comparison with previously measured values is given, and the accuracy and repeatability of the method are discussed.Paper presented at the Seventeenth European Conference on Thermophysical Properties, September 5–8, 2005, Bratislava, Slovak Republic.     

Thermal conductivity of steam from 250 to 510°C at pressures up to 95 MPa including the critical region

New measurements of the thermal conductivity of steam have been performed in the temperature range 250–510°C and in the pressure range from 1 up to 95 MPa. Most of the measurements were taken at temperatures greater than the critical temperature, where the enhancement of the thermal conductivity is observed. The experimental values are compared to the IAPS formulation for the thermal conductivity of water.     

Determination of the thermal conductivity of argon and nitrogen over a wide temperature range through data evaluation and shock-tube experiments

Reliable and well-established methods to measure the thermal conductivity of gases are available only in the moderate temperature range, namely, up to about 1000 K. In the present study, a set of the most probable thermal conductivity values of components of gaseous combustion products in a wide range of temperatures has been obtained through an optimum combination of three procedures: critical assessment of available data in the moderate temperature range, experimental determination by the shock-tube method at high temperatures, and theoretacal estimation of temperature dependence in the intermediate temperature range. Among the components of combustion products, one monatomic gas and one diatomic gas, namely, argon and nitrogen, were studied in the present paper. The shock-tube measurements have been performed in the temperature ranges 1000–4500 K for argon and 500–2200 K for nitrogen. The results of the critical evaluation and the shock-tube measurements have been combined with the aid of theoretically assumed temperature dependence of the thermal conductivity.Invited paper presented at the Ninth Symposium on Thermophysical Properties, June 24–27, 1985, Boulder, Colorado, U.S.A.     

The transport properties of ethane. II. Thermal conductivity

A new representation of the thermal conductivity of ethane is presented. The representative equations are based upon a body of experimental data that have been critically assessed for internal consistency and for agreement with theory in the zero-density limit and in the critical region. The representation extends over the temperature range from 100 K to the critical temperature in the liquid phase and from 225 K to the critical temperature in the vapor phase. In the supercritical region the temperature range extends to 1000 K for pressures up to 1 MPa and to 625 K for pressures up to 70 MPa. The ascribed accuracy of the representation varies according to the thermodynamic state from ±2% for the thermal conductivity of the dilute gas near room temperature to ±5% for the thermal conductivity at high pressures and temperatures. Tables of the thermal conductivity, generated by the relevant equations, at selected temperatures and pressures and along the saturation line are also provided.     

The Thermal Conductivity, Thermal Diffusivity, and Heat Capacity of Gaseous Argon

This paper presents new absolute measurements for the thermal conductivity and thermal diffusivity of gaseous argon obtained with a transient hot-wire instrument. Six isotherms were measured in the supercritical dense gas at temperatures between 296 and 423 K and pressures up to 61 MPa. A new analysis for the influence of temperature-dependent properties and residual bridge unbalance is used to obtain the thermal conductivity with an uncertainty of less than 1% and the thermal diffusivity with an uncertainty of less than 4%. Isobaric heat capacity results were derived from measured values of thermal conductivity and thermal diffusivity using a density calculated from an equation of state. The heat capacities presented here have a nominal uncertainty of 4% and demonstrate that this property can be obtained successfully with the transient hot wire technique over a wide range of fluid states. The technique will be useful when applied to fluids which lack specific heat data.     

The thermal conductivity and heat capacity of gaseous argon

This paper presents new absolute measurements of the thermal conductivity and of the thermal diffusivity of gaseous argon obtained with a transient hot-wire instrument. We measured seven isotherms in the supercritical dense gas at temperatures between 157 and 324 K with pressures up to 70 MPa and densities up to 32 mol · L^–1 and five isotherms in the vapor at temperatures between 103 and 142 K with pressures up to the saturation vapor pressure. The instrument is capable of measuring the thermal conductivity with an accuracy better than 1% and thermal diffusivity with an accuracy better than 5%. Heat capacity results were determined from the simultaneously measured values of thermal conductivity and thermal diffusivity and from the density calculated from measured values of pressure and temperature from an equation of state. The heat capacities presented in this paper, with a nominal accuracy of 5%, prove that heat capacity data can be obtained successfully with the transient hot wire technique over a wide range of fluid states. The technique will be invaluable when applied to fluids which lack specific heat data or an adequate equation of state.     

Thermal Conductivity and Thermal Diffusivity of Pulse-Heated W–Re Alloys

Results are reported for the thermal conductivity and thermal diffusivity as a function of temperature for four W–Re alloys (4.0, 21.24, 24.07, and 31.09 mass% of Re) over a wide temperature range covering the solid and liquid states. The measurements allow the determination of specific heat and dependences among electrical resistivity, temperature, and density of the alloys into the liquid phase. The thermal conductivity is calculated using the Wiedeman–Franz law. Additionally, data for thermal conductivity and thermal diffusivity of the constituent elements, tungsten and rhenium, are presented for the first time. Both metals have been previously studied with the same experimental technique.     

Thermal conductivity of hydrogen for temperatures between 78 and 310 K with pressures to 70 MPa

The paper presents new experimental measurements of the thermal conductivity of hydrogen. The ortho-para compositions covered are normal, near normal, para, and para-rich. The measurements were made with a transient hot wire apparatus. The temperatures covered the range from 78 to 310 K with pressures to 70 MPa and densities from 0 to a maximum of 40 mol · L^–1. For compositions normal and near normal, the isotherms cover the entire range of pressure, and the temperatures are 78, 100, 125, 150, 175, 200, 225, 250, 275, 294, 300, and 310K. The para measurements include eight isotherms at temperatures from 100 to 275 K with intervals of 25 K, pressures to 12 MPa, and densities from 0 to 12 mol · L^–1. Three additional isotherms at 150, 250, and 275 K cover para-rich compositions with para percentages varying from 85 to 72%. For these three isotherms the pressures reach 70 MPa and the density a maximum of 30 mol · L^–1. The data for all compositions are represented by a single thermal conductivity surface. The data are compared with the experimental measurements of others through the new correlation. The precision (2) of the hydrogen measurements is between 0.5 and 0.8% for wire temperature transients of 4 to 5 K, while the accuracy is estimated to be 1.5%.