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.     

Thermal conductivity and thermal diffusivity of xylene isomers in the temperature range 308–360 K at pressures up to 0.38 GPa

New, absolute measurements of the thermal conductivity of the three xylene isomers within the temperature range 308–360 K for pressures up to 0.38 GPa are reported. In addition, for two of the isomers, m-xylene and p-xylene, it has been possible to measure the thermal diffusivity simultaneously within the same range of conditions. The accuracy of the thermal conductivity data reported is one of ±0.3%, whereas for the thermal diffusivity the estimated accuracy is ±6%. It is found that the density dependence of the thermal conductivity for all of the xylenes can be well represented by one equation based on a rigid-sphere model in the same way that has proved successful for normal alkanes. The thermal diffusivity data have been employed to derive heat capacities for the xylenes over a range of pressures.     

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     

Thermal conductivity andPVT measurements of pentafluoroethane (refrigerant HFC-125)

By means of the transient and steady-state coaxial cylinder methods, the thermal conductivity of pentafluoroethane was investigated at temperatures from 187 to 419 K and pressures from atmospheric to 6.0 MPa. The estimated uncertainty of the measured results is ±(2–3)%. The operation of the experimental apparatus was validated by measuring the thermal conductivity of R22 and R12. Determinations of the vapor pressure andPVT properties were carried out by a constant-volume apparatus for the temperature range 263 to 443 K, pressures up to 6 MPa, and densities from 36 to 516 kg m^–3. The uncertainties in temperature, pressure, and density are less than ±10 mK, ±0.08%, and ±0.1%, respectively.Paper presented at the Twelfth Symposium on Thermophysical Properties, June 19–24, 1994, Boulder, Colorado, U.S.A.     

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.     

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.     

Measurement of the Thermal Conductivity of Liquid Dimethoxymethane from 240 to 362 K

The thermal conductivity of liquid dimethoxymethane was measured by the transient hot-wire method using a bare platinum wire in a temperature range from 240 to 360 K. The experimental data were fitted by a function of temperature. The average absolute deviation of experimental data from those calculated by the equation was 0.18%, and the maximum deviation was 0.41%. The uncertainty of the thermal conductivity was less than ± 2% with a coverage factor of k = 2. The uncertainty of the temperature was within ± 10 mK (k = 2).     

Thermal conductivity of n-tridecane at pressures up to 500 MPa in the temperature range 35–75°C

Thermal conductivity coefficients are reported for liquid n-tridecane along three isotherms, 35, 48, and 73°C, and for pressures from 20 to 500 MPa. The measurements have been made with a transient hot-wire instrument, and the results, when corrected for the effects of radiation absorption, have an estimated uncertainty of ±0.7%. The thermal conductivity as a function of density along isotherms can be represented by means of the same form of equation as that found suitable for other normal alkanes, and this is based upon a heuristic modification of the van der Waals theory of liquids.     

Thermal conductivity of fourteen liquids in the temperature range 298–373 K

New experimental data on the thermal conductivity of 14 organic liquids at atmospheric pressure are presented in the temperature range from 25 to 100°C. The liquids measured are five n-alkanes (C₆, C₇, C₈, C₁₀, C₁₂), cyclohexane, six aromatic hydrocarbons (benzene, ethylbenzene, o-, m-, p-xylenes, isopropylbenzene) and two phenyl halides (chloro-, bromobenzenes). The measurements were performed by a transient hot-wire method on a relative basis. The thermal conductivity of toluene, which was selected as a reference liquid, was determined on an absolute basis with another transient apparatus. The precision of the present experimental results is within ±1.2%. The uncertainty of the thermal conductivity values is estimated to be within ±2%; this includes the uncertainty of the values of toluene as the reference liquid. The experimental results for each liquid are represented satisfactorily by a linear equation in temperature. At a reduced temperature T/T _c=0.5, thermal conductivity has a simple relation with the molar density for each homologous series of liquids.     

Comparison of thermal conductivity data for partially stabilized zirconia with values derived from thermal diffusivity results

The thermal conductivity of partially stabilized zirconia was measured over the temperature range 320–1273 K using the radial heat flow method. The data have an absolute uncertainty of about ±2% and repeat measurements showed no evidence of changes in the thermal conductivity at high temperatures. This also was true for the thermal diffusivity data, which were obtained in vacuum over the temperature range 300–1473 K. Both sets of thermal conductivity data pass through minima at high temperatures. Quantitative differences were observed in the temperatures and thermal conductivities of the two minima. The results were analyzed by assuming parallel conduction by phonons and photons, and the phonon component was identified by fitting lower-temperature data. Extrapolating this curve allowed identification of the photon contribution to the thermal conductivity at high temperatures. The photon contribution approached a T ³ function and was larger in the thermal conductivity specimens. The difference in the photon contributions correlates with changes in the optical properties of the samples produced during the high temperature measurments.     

Thermophysical Properties of 1,1,1,3,3-Pentafluorobutane (R365mfc)

This paper presents an experimental study on various thermophysical properties of a new fluoroalkane, 1,1,1,3,3-pentafluorobutane (R365mfc). The thermal conductivity of R365mfc was measured in the liquid phase near saturation conditions at temperatures between 263 and 333 K using a parallel plate instrument with an uncertainty of less than ±5%. For the measurement of the saturated liquid density between 273 and 353 K, a vibrating tube instrument was used. The uncertainty of the density measurements is less than ±0.1%. In addition, experimental data have been obtained for R365mfc under saturation conditions over a wide temperature range from about 253 to 460 K using light scattering techniques. Light scattering from the bulk fluid has been applied for measuring both the thermal diffusivity and the sound speed in the liquid and vapor phases. Light scattering by surface waves on a horizontal liquid–vapor interface has been used for the simultaneous determination of the surface tension and kinematic viscosity of the liquid phase. With the light scattering techniques, uncertainties of less than ±1.0, ±0.5, ±1.0, and ±1.2% have been achieved for the thermal diffusivity, the sound speed, the kinematic viscosity, and the surface tension, respectively.     

An Improved Empirical Correlation for the Thermal Conductivity of Propane

New experimental data on the thermal conductivity of propane have been reported since the wide-range correlations proposed by Holland et al. and by Younglove and Ely. These new experimental data, covering a temperature range of 110 to 700 K and a pressure range of 0.1 to 70 MPa, are used together with the previously available data to develop an improved empirical equation for the thermal conductivity of gaseous and liquid propane. The quality of the new data is such that the thermal-conductivity correlation for propane is estimated to have an uncertainty of about ±5% at a 95% confidence level, with the exception of state points near the critical point, where the uncertainty of the correlation increases to ±10%.     

Experimental determination of the thermal diffusivity of molten alkali halides by the forced Rayleigh scattering method. I. Molten LiCl,NaCl, KCl,RbCl, and CsCl

As a series of experimental determinations of the thermal diffusivity of molten alkali halides, this paper describes measurements on five molten alkali metal chlorides (LiCl, NaCl, KCl, RbCl, and CsCl) in the temperature range up to 1440 K by the forced Rayleigh scattering method. K₂Cr₂O₇ is employed as a dye substance to color the transparent molten salts. The accuracy is estimated to be ± 4 to ±11 % depending on the measured salts. In comparison with the present results converted into thermal conductivity, most of the previous experimental data obtained by steady-state methods show larger values, up to about five times, which may be due to the systematic error caused by the presence of convection and radiation. It is found that the thermal conductivity of these series of molten alkali metal chlorides decreases with increasing molecular weight, and their temperature coefficients are weakly negative.     

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.     

A High-Temperature Transient Hot-Wire Thermal Conductivity Apparatus for Fluids

A new apparatus for measuring both the thermal conductivity and thermal diffusivity of fluids at temperatures from 220 to 775 K at pressures to 70 MPa is described. The instrument is based on the step-power-forced transient hot-wire technique. Two hot wires are arranged in different arms of a Wheatstone bridge such that the response of the shorter compensating wire is subtracted from the response of the primary wire. Both hot wires are 12.7 µm diameter platinum wire and are simultaneously used as electrical heat sources and as resistance thermometers. A microcomputer controls bridge nulling, applies the power pulse, monitors the bridge response, and stores the results. Performance of the instrument was verified with measurements on liquid toluene as well as argon and nitrogen gas. In particular, new data for the thermal conductivity of liquid toluene near the saturation line, between 298 and 550 K, are presented. These new data can be used to illustrate the importance of radiative heat transfer in transient hot-wire measurements. Thermal conductivity data for liquid toluene, which are corrected for radiation, are reported. The precision of the thermal conductivity data is ± 0.3% and the accuracy is about ±1%. The accuracy of the thermal diffusivity data is about ± 5%. From the measured thermal conductivity and thermal diffusivity, we can calculate the specific heat, C_p, of the fluid, provided that the density is measured, or available through an equation of state.     

Thermal Diffusivity Measurements on Insulation Materials with the Laser Flash Method

An iterative approach is adopted to determine the thermal diffusivity of the xonotlite-type calcium silicate insulation material with very low thermal conductivity. The measurements were performed with a conventional laser flash apparatus by rear-face detection of the temperature response of the three-layered sample, where the insulating material is sandwiched between two iron slices. In the evaluation of the thermal conductivity, the theoretical curve is fitted to the complete temperature–time curve, instead of just using the t _1/2 point. The theoretical model is based on the thermal quadrupole method. The nonlinear parameter estimation technique is used to estimate simultaneously the thermal diffusivity, heat transfer coefficient, and absorbed energy. Based on experimental results, the optimal thickness range of the insulation material in the sample is indicated as 1.6 to 1.9 mm. The effects of the uncertainties of the thicknesses, contact resistance, and thermophysical properties of the three layers on the measurement uncertainty are estimated, giving an overall uncertainty in the thermal conductivity of approximately 7.5%.Paper presented at the Seventh Asian Thermophysical Properties Conference, August 23–28, 2004, Hefei and Huangshan, Anhui, P. R. China.     

Thermal conductivity of isopentane in the temperature range 307–355 K at pressures up to 0.4 GPa

This paper reports the results of new, absolute measurements of thermal conductivity of isopentane in the temperature range 307–335 K at pressures up to 0.4 GPa. The experimental data have an estimated uncertainty of ±0.3%. The density dependence of the thermal conductivity along the various isotherms has been represented with the aid of a single universal equation derived for a series of alkanes and based upon the hard-sphere model of dense fluids. An even more general prediction scheme for the thermal conductivity of liquids developed initially for normal alkanes is found to predict the present data within ±5%.     

Absolute measurement of the thermal conductivity of alcohol + n-hexane mixtures

New absolute measurements, by the transient hot-wire technique, of the thermal conductivity of binary mixtures of n-hexane with methanol, ethanol, and hexanol are presented. The temperature range examined was 295–345 K and the pressure atmospheric. The concentrations studied were 75% by weight of methanol and 25, 50, and 75% by weight of ethanol and hexanol. The overall uncertainty in the reported thermal conductivity data is estimated to be ±0.5%, an estimate confirmed by the measurement of the thermal conductivity of water. A recently extended semiempirical scheme for the prediction of the thermal conductivity of mixtures from the pure components is used to correlate and predict the thermal conductivity of these mixtures, as a function of both composition and temperature.     

Evaluation of the Heat Leakage in the Thermal Diffusivity Measurement of Molten Metals by a Laser Flash Method

Evaluation of the radiative and conductive heat loss from a molten metal sample to the cell has been made in order to obtain accurate thermal diffusivities of molten metals at high temperature with a laser flash method. The results suggest that thermal diffusivity values of molten nickel can be determined in the temperature range from 1728 to 1928 K with an uncertainty of ±3% in comparison with case considering only the effect of radiative heat loss. The usefulness of a cell for a laser flash method has been confirmed by applying simulated results to evaluate the heat leakage in the thermal diffusivity measurement of molten metals.     

Thermal Conductivity of HFC-32, HFC-125, and HFC-134a in the Solid Phase

Measurements of the thermal conductivity of HFC-32, HFC-125, and HFC-134a were carried out for the first time in both solid and liquid phases at the saturation pressure at room temperature and in the temperature ranges from 120 to 263, from 140 to 213, and from 130 to 295 K, respectively. A transient hot-wire instrument using one bare platinum wire was employed for measurements, with an uncertainty of less than ±2%. The experimental results demonstrated that the thermal conductivity of HFC-32, HFC-125, and HFC-134a in the solid phase showed a positive temperature dependence. For HFC-32 and HFC-125, there were big jumps between the solid and the liquid thermal conductivity at the melting point. But for HFC-134a, the solid and liquid thermal conductivity at the melting point is almost-continuous.