Thermophysical Properties of Diorites along with the Prediction of Thermal Conductivity from Porosity and Density Data

The main focus of this paper involves the use of models to predict the thermophysical properties of diorites. For the prediction of thermal conductivity, an existing mixing law and empirical models have been used. Due to the porosity dependence in all the existing models, ASTM (American Society for Testing and Materials) standard methods have been applied to measure the density, porosity, and specific gravity of diorite rocks taken from the Shewa-Shahbaz Garhi volcanic complex near Mardan, Pakistan. The chemical composition of these samples has been analyzed using the X-ray florescence technique. The theoretically calculated values of specific gravity and the density of the specimen based on the chemical composition and porosity are in good agreement with those obtained from experimental measurements at ambient conditions. The thermal conductivity and thermal diffusivity of these rocks have been measured simultaneously using the transient plane source (TPS) technique at room temperature. The effective thermal conductivity calculated from various models is in agreement with the experimental data within 15%. Simple correlations between estimated density and porosity and between the effective thermal conductivity and porosity are also established.     

Modeling of the Effective Thermal Conductivity of Consolidated Porous Media with Different Saturants: A Test Case of Gabbro Rocks

The thermal conductivity and thermal diffusivity of porous consolidated gabbro rocks have been measured simultaneously by the transient plane source technique at normal temperature and pressure using air and water as saturants. The density and porosity are measured using American Society for Testing and Materials (ASTM) standards under ambient conditions. The mineral composition is obtained using a petrography technique. Data are presented for 12 specimens of gabbro, taken from Warsik near Peshawar, Pakistan. A recently proposed empirical model for the prediction of the thermal conductivity of porous consolidated igneous rocks is established using different fluids in pore spaces, under ambient conditions. An exponential decay formula is also proposed for the prediction of the thermal conductivity at room temperature and normal pressure. The results are compared with different existing empirical models. A simple correlation between density and porosity is also reported.     

Simultaneous Measurements of the Thermal Conductivity and Thermal Diffusivity of Molten Salts with a Transient Short-Hot-Wire Method

A transient short-hot-wire technique has been successfully used to measure the thermal conductivity and thermal diffusivity of molten salts (NaNO₃, Li₂CO₃/K₂CO₃, and Li₂CO₃/Na₂CO₃) which are highly corrosive. This method was developed from the hot-wire technique and is based on two-dimensional numerical solutions of unsteady heat conduction from a short wire with the same length-to-diameter ratio and boundary conditions as those used in the actual experiments. In the present study, the wires are coated with a pure Al₂O₃ thin film by using a sputtering apparatus. The length and radius of the hot wire and the resistance ratio of the lead terminals and the entire probe are calibrated using water and toluene with known thermophysical properties. Using such a calibrated probe, the thermal conductivity and thermal diffusivity of molten nitrate are measured within errors of 3 and 20%, respectively. Also, the thermal conductivity of the molten carbonates can be measured within an error of 5%, although the thermal diffusivity can be measured within an error of 50%.     

Measurements of Thermal Conductivity and Thermal Diffusivity of CVD Diamond

The thermal conductivity of natural, gem-quality diamond, which can be as high as 2500 Wm^–1 K^–1 at 25°C, is the highest of any known material. Synthetic diamond grown by chemical vapor deposition (CVD) of films up to 1 mm thick exhibits generally lower values of but under optimal growth conditions it can rival gem-quality diamond with values up to 2200 Wm^–1 K^–1. However, it is polycrystalline and exhibits a columnar microstructure. Measurements on free-standing CVD diamond, with a thickness in the range 25–400 m, reveal a strong gradient in thermal conductivity as a function of position z from the substrate surface as well as a pronounced anisotropy with respect to z. The temperature dependence of in the range 4 to 400 K has been analyzed to determine the types and numbers of phonon scattering centers as a function of z. The defect structure, and therefore the thermal conductivity, are both correlated with the microstructure. Because of the high conductivity of diamond, these samples are thermally thin. For example, laser flash data for a 25-m-thick diamond sample is expected to be virtually the same as laser flash data for a 1-m-thick fused silica sample. Several of the techniques described here for diamond are therefore applicable to much thinner samples of more ordinary material.     

Modeling of Effective Thermal Conductivity of Dunite Rocks as a Function of Temperature

The thermal conductivity, thermal diffusivity, and heat capacity per unit volume of dunite rocks taken from Chillas near Gilgit, Pakistan, have been measured simultaneously using the transient plane source technique. The temperature dependence of the thermal transport properties was studied in the temperature range from 303 K to 483 K. Different relations for the estimation of the thermal conductivity are applied. A proposed model for the prediction of the thermal conductivity as a function of temperature is also given. It is observed that the values of the effective thermal conductivity predicted by the proposed model are in agreement with the experimental thermal conductivity data within 9%.     

Measurements of the Thermal Conductivity and Thermal Diffusivity of Polymer Melts with the Short-Hot-Wire Method

In this paper, the thermal conductivity and thermal diffusivity of four kinds of polymer melts were measured by using the transient short-hot-wire method. This method was developed from the hot-wire technique and is based on two-dimensional numerical solutions of unsteady heat conduction from a wire with the same length-to-diameter ratio and boundary conditions as those in the actual experiments. The present method is particularly suitable for measurements of molten polymers where natural convection effects can be ignored due to their high viscosities. The results have shown that the present method can be used to measure the thermal conductivity and thermal diffusivity of molten polymers within uncertainties of 3 and 6%, respectively. Further, the thermal conductivity and thermal diffusivity of solidified samples were also measured and discussed.     

Thermal Conductivity of Toluene+Cyclopentane Mixtures: Measurements and Prediction

New measurements of the thermal conductivity of toluene, cyclopentane, and a binary mixture of 60 wt% toluene are presented. The measurements cover the temperature range from 235 to 345 K and from the saturation line up to 20 MPa pressure. The measurements were performed with a transient hot-wire instrument. The uncertainty of the measurements is estimated to be ±0.5%. The present results are employed to examine the predictive power of a theoretically based scheme for the calculation of the transport properties of mixtures.     

Measurement of the Thermal Conductivity and Thermal Diffusivity of Liquids. Part I: “Pure Conduction and an Example of a Solution”

The measurement of the thermal conductivity of liquids is rather complicated due to the nature of the fluid. To the conduction, which has to be characterized, are added the natural convection, the radiative transfer, and the perturbations caused by the presence of enclosure walls. The goal of this work, composed of two parts, is to implement an experimental bench allowing the measurement of the thermal diffusivity and thermal conductivity of liquids. The first part (Part I) presented here, is about pure conduction and focuses on several aspects involved in this measurement, which will lead one, based on theoretical and practical considerations, to choose a pulse method in a one-dimensional (1D) and cylindrical geometry to solve the problem. In the second section of this part, the problem of the parameters estimation is investigated with the presence of the walls of the measuring cell and this will allow us to define the characteristics of the walls (thickness and thermophysical properties). The entire problem is treated through the thermal quadrupoles method. Finally, in a last section, a setup at room temperature is described. The second part (Part II) of this work that is presented in another paper will show how it is possible to get rid of the convection by a judicious choice of the extension of the measuring cell and how the radiation effects can be taken into account to perform measurements at high temperatures (up to 500°C).Paper presented at the Seventh Asian Thermophysical Properties Conference, August 23–28, 2004, Hefei and Huangshan, Anhui, P. R. China.     

Intercomparison of Measurements of the Thermophysical Properties of Polymethyl Methacrylate

Results of an intercomparison of measurements of thermal conductivity, thermal diffusivity, specific heat capacity, and density of polymethyl methacrylate (PMMA) in the temperature range between –70°C and +80°C are presented. The purpose of this comparison is to investigate the variability of the results among guarded hot-plate (GHP) and guarded heat-flow meter (GHF) techniques on the one hand and among GHP/GHF and other measuring instruments on the other. The primary objectives are to characterize the material properties mentioned and to quantify the effects of thermal contact resistances and temperature measurements. With regard to future use of PMMA as a reference material, reference data for the thermal conductivity are derived.     

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.     

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

Low-pressure thermal conductivity and thermal diffusivity measurements are reported for argon and nitrogen in the temperature range from 295 to 350 K at pressures from 0.34 to 6.9 MPa using an absolute transient hot-wire instrument. Thermal conductivity measurements were also made with the same instrument in its steady-state mode of operation. The measurements are estimated to have an uncertainty of 1% for the transient thermal conductivity, 3% for the steady-state thermal conductivity, and 4% for thermal diffusivity. The values of isobaric specific heat, derived from the measured thermal conductivity and thermal diffusivity, are considered accurate to 5% although this is dependent upon the uncertainty of the equation of state utilized.Paper presented at the Sixteenth European Conference on Thermophysical Properties, September 1–4, 2002, London, United Kingdom     

The Thermal Conductivity, Thermal Diffusivity and Isobaric Heat Capacity of Toluene and Argon

This paper presents absolute measurements for the thermal conductivity and thermal diffusivity of toluene obtained with a transient hot-wire instrument employing coated wires over the density interval of 735 to 870 kgm^–3. A new expression for the influence of the wire coating is presented, and an examination of the importance of a nonuniform wire radius is verified with measurements on argon from 296 to 323 K at pressures to 61 MPa. Four isotherms were measured in toluene between 296 and 423 K at pressures to 35 MPa. The measurements have an uncertainty of less than ±0.5% for thermal conductivity and ±2% for thermal diffusivity. Isobaric heat capacity results, derived from the measured values of thermal conductivity and thermal diffusivity, using a density determined from an equation of state, have an uncertainty of ±3% after taking into account the uncertainty of the applied equation of state. The measurements demonstrate that isobaric specific heat determinations can be obtained successfully with the transient hot wire technique over a wide range of fluid states provided density values are available.     

Experimental Study on the Effective Thermal Conductivity and Thermal Diffusivity of Nanofluids

This paper reports measurements of the effective thermal conductivity and thermal diffusivity of various nanofluids using the transient short-hot-wire technique. To remove the influences of the static charge and electrical conductance of the nanoparticles on measurement accuracy, the short-hot-wire probes are carefully coated with a pure Al₂O₃ thin film. Using distilled water and toluene as standard liquids of known thermal conductivity and thermal diffusivity, the length and radius of the hot wire and the thickness of the Al₂O₃ film are calibrated before and after application of the coating. The electrical leakage of the short-hot-wire probes is frequently checked, and only those probes that are coated well are used for measurements. In the present study, the effective thermal conductivities and thermal diffusivities of Al₂O₃/water, ZrO₂/water, TiO₂/water, and CuO/water nanofluids are measured and the effects of the volume fractions and thermal conductivities of nanoparticles and temperature are clarified. The average diameters of Al₂O₃, ZrO₂, TiO₂, and CuO particles are 20, 20, 40, and 33 nm, respectively. The uncertainty of the present measurements is estimated to be within 1% for the thermal conductivity and 5% for the thermal diffusivity. The measured results demonstrate that the effective thermal conductivities of the nanofluids show no anomalous enhancement and can be predicted accurately by the model equation of Hamilton and Crosser, when the spherical nanoparticles are dispersed into fluids.     

相对湿度对泡沫玻璃导热系数的影响

采用瞬态平面热源法在不同的环境相对湿度下对3对泡沫玻璃的导热系数进行了测量。实验结果表明,在相对湿度较低的情况下,试样的导热系数受湿度影响较小,几乎不随环境湿度变化;在相对湿度较高的情况下,试样的导热系数随湿度的增大而增大,与低湿度时相比导热系数最多增大了近1.5%;此外,实验结果还表明泡沫玻璃的导热系数存在不均匀性,不同区域的导热系数值存在较大差别,最大可相差8.8%。     

The Thermal Conductivity, Thermal Diffusivity, and Specific Heat of Liquid n-Pentane

The thermal conductivity and thermal diffusivity of liquid n-pentane have been measured over the temperature range from 293 to 428 K at pressures from 3.5 to 35 MPa using a transient hot-wire instrument. It was determined that the results were influenced by fluid thermal radiation, and a new expression for this effect is presented. The uncertainty of the experimental results is estimated to be better than ±0.5% for thermal conductivity and ±2% for thermal diffusivity. The results, corrected for fluid thermal radiation, are correlated as functions of temperature and density with a maximum uncertainty of ±2% for thermal conductivity and ±4% for thermal diffusivity. Derived values of the isobaric specific heat are also given.     

Thermal Transport Properties of Layered Materials: Identification by a New Numerical Algorithm for Transient Measurements

Transient methods are widely used to determine thermal transport properties. In some situations they can be used for homogeneous media to measure several properties either simultaneously or separately. In this context an analytic model is available and a well-posed inverse problem of parameter identification has to be solved. The examination of composite media is more complicated. The algorithm proposed here allows simultaneous determination of the thermal conductivity and thermal diffusivity of layered dielectrics by transient measurements. It is based on a plane source that acts both as a resistive heater and temperature sensor. For the technique to be successful two essential aspects have to be considered: firstly, the mathematical modeling of the measured data (the forward problem) and secondly, the problem of ill-posedness of the inverse problem. For the proposed measurement configuration, a new fast data analysis algorithm based on an analytic solution for the forward problem is presented. In principle, a numerical solution such as an FEM solution of the heat conduction equation can be used instead of the analytical one, but the computational effort is much greater. The inverse problem is formulated as an output-least-squares problem, which leads to a transcendent algebraic system of equations. The method was successfully tested for different situations.Paper presented at the Fifteenth Symposium on Thermophysical Properties, June 22--27, 2003, Boulder, Colorado, U.S.A.     

Application of the Multi-Current Transient Hot-Wire Technique for Absolute Measurements of the Thermal Conductivity of Glycols

Experimental measurements of the thermal conductivity of mono-, di-, tri-, and tetra-ethylene glycol are presented. The experiments were carried out at atmospheric pressure and at temperatures ranging from 25 to 65°C. The multi-current transient hot-wire technique has been used with a platinum wire of 25 μm diameter; the electrical current varied from 25 to 75 mA. For all studied glycols, it was found that the thermal conductivity increases with temperature and decreases with the glycol molar mass. The random uncertainty of the reported experimental thermal conductivity data is less than 0.9%. The estimated systematic errors affecting the obtained data are at most 2%. The values obtained in this study were compared with previously published results for the four glycols, finding deviations of the order of 2%.     

Measurement and Analysis of Thermophysical Properties of Diorites in the Temperature Range from 253 to 333 K

Thermal conductivity and thermal diffusivity are simultaneously measured for a collection of diorite samples taken from Shewa-Shahbaz Garhi volcanic complex near Mardan, Pakistan by using the transient plane source (TPS) technique. The temperature dependence of the transport properties of these samples is studied in the temperature range from 253 to 333 K. Different relationships for the temperature dependence of the thermal conductivity and thermal diffusivity are tested. The samples are also characterized by their chemical composition, density, porosity, and specific gravity at room temperature and atmospheric pressure. Theoretical calculation of the specific gravity parameter based on the chemical composition is in good agreement with the experimental observation. No correlation was found for the temperature dependence of the thermal transport behavior on porosity, chemical composition, and density.     

A New Pulse Hot Strip Sensor for Measuring Thermal Conductivity and Thermal Diffusivity of Solids

The pulse hot strip method is a newly developed dynamic method to measure the thermal conductivity and thermal diffusivity of solids. It is based on monitoring the temperature response of a sample to a very short heat pulse liberated by a strip heat source. The instrument's uncertainty is estimated to be less than 3% for both quantities.     

Measurement of Thermal Transport Properties with an Improved Transient Plane Source Technique

The transient plane source (TPS) technique has been revised with the aim of developing a simple and fast system to measure the thermal transport properties of materials at low temperatures, especially high-T _c superconductors. To ensure reliable results, any new system should be tested with known samples. Fused silica, 0.9% carbon steel (215/3), and halide crystals (silver chloride) were studied with the new setup to check its performance. Data were taken from room temperature down to liquid nitrogen temperature. The assembly was designed for cryogenic (79 to 300 K) measurements in an atmosphere free of humidity. Dry nitrogen gas was used as a heat transfer medium around the sample holder assembly. The measured values for thermal conductivity and thermal diffusivity of these samples are in excellent agreement with values reported earlier. The thermal conductivity and thermal diffusivity for silver chloride crystals are extended down to 80 K although recommended data were available only down to 220 K. A Ba-doped, Bi-based, high-T _c superconductor was prepared by a solid-state reaction method. The nominal composition used was Bi_1.6Pb_0.4Sr_1.6Ba_0.4Ca₂Cu₃O_y. Large-sized samples (diameter 28mm and length 11mm) are investigated for thermal transport properties.