Thermal conductivity of R32 and R125 in the liquid phase at the saturation vapor pressure

The first measurements of the thermal conductivity of two refrigerants which are candidates for the replacement of those fluids currently in use are reported. Specifically, results are given for the thermal conductivity of R32 and R125 in the liquid phase along the saturation line. The measurements, which have been made by the transient hot-wire technique, extend over the temperature range from 205 to 303 K for R32 and from 225 to 306 K for R125; the results have an estimated uncertainty of ±1.0%.     

Measurements of the thermal conductivity of refrigerants in the vapor phase

Measurements of the thermal conductivity of refrigerants R124, R125, and R134a in the vapor phase are presented. The measurements, performed in a newly developed transient hot-wire instrument, cover a temperature range from 273 to 333 K and a pressure range from about atmospheric up to below the saturation pressure. A finite-elements program developed allowed the reexamination of the major corrections employed in the analysis of the results. The uncertainty of the reported values is estimated to be better than ±1%. Comparisons with measurements of other investigators along the saturation line show a lack of reliable thermal conductivity data in the vapor phase for these compounds. Invited paper presented at the Fourth Asian Thermophysical Properties Conference, September 5–8, 1995, Tokyo, Japan.     

The thermal conductivity of liquid 1,1,1,2-tetrafluoroethane (HFC 134a)

The thermal conductivity of HFC 134a was measured in the liquid phase with the polarized transient hot-wire technique. The experiments were performed at temperatures from 213 to 293 K at pressures up to 20 MPa. The data were analyzed to obtain correlations in terms of density and pressure. This study is part of an international project coordinated by the Subcommittee on Transport Properties of Commission 1.2 of IUPAC, conducted to investigate the large discrepancies between the results reported by various authors for the transport properties of HFC 134a, using samples of different origin. Two samples of HFC 134a from different sources have been used. The thermal conductivity of the first sample was measured along the saturation line as a function of temperature and the data were presented earlier. The thermal conductivity of the second one, the round-robin sample was measured as a function of pressure and temperature. These data were extrapolated to the saturation line and compared with the data obtained, previously in order to demonstrate the importance of the sample origin and their real purity. The accuracy of the measurements is estimated to be 0.5%. Finally, the results are compared with the existing literature data.     

Thermal Conductivity of Saturated Liquid Toluene by Use of Anodized Tantalum Hot Wires at High Temperatures

Absolute measurements of the thermal conductivity of a distilled and dried sample of toluene near saturation are reported. The transient hot-wire technique with an anodized tantalum hot wire was used. The thermal conductivities were measured at temperatures from 300 K to 550 K at different applied power levels to assess the uncertainty with which it is possible to measure liquid thermal conductivity over wide temperature ranges with an anodized tantalum wire. The wire resistance versus temperature was monitored throughout the measurements to study the stability of the wire calibration. The relative expanded uncertainty of the resulting data at the level of 2 standard deviations (coverage factor k = 2) is 0.5 % up to 480 K and 1.5 % between 480 K and 550 K, and is limited by drift in the wire calibration at temperatures above 450 K. Significant thermal-radiation effects are observed at the highest temperatures. The radiation-corrected results agree well with data from transient hot-wire measurements with bare platinum hot wires as well as with data derived from thermal diffusivities obtained using light-scattering techniques.     

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 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.     

Thermal Conductivity of Aqueous Potassium Chloride Solutions

This paper presents new absolute measurements of the thermal conductivity of aqueous potassium chloride solutions using the transient coated-hot-wire technique. The data cover the range from 295 to 360 K at pressures slightly above the vapor pressures and over a concentration range of 0 to 3 mol·kg^–1. The instrument can be used to measure the thermal conductivity with a reproducibility of better than 0.2%, and a comparison of the present results with data available in the literature indicates that the uncertainty of the present data is better than 0.5%. An empirical correlation that reproduces the data within the claimed uncertainty is presented.     

Thermal conductivity of liquids: Prediction based on a group-contribution scheme

A new semiempirical predictive scheme for the thermal conductivity of liquids, based on an extension of concepts derived from the rigid-sphere model of dense-fluid transport properties, is presented. The scheme makes use of the idea of group contributions to the molecular volume and is developed with the aid of accurate thermal conductivity data for the alkanes, the aromatic hydrocarbons, the alcohols, and the diols, along the saturation line and at elevated pressures. The procedure has been tested against other thermal conductivity data, not included in its formulation, and has been found to predict values within ±4% of the experimental data in the temperature range 110–370 K for pressures up to 600 MPa.     

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%.     

Thermal diffusivity and thermal conductivity of toluene by photon correlation spectroscopy: A test of the accuracy of the method

Absolute measurements of the thermal diffusivity of liquid toluene were performed by photon correlation spectroscopy between 393 and 523 K near the saturation line. The experimental method is based on a time-resolved analysis of the laser light scattered from local equilibrium fluctuations in a transparent sample. enabling us to obtain the thermal diffusivity in macroscopic thermodynamic equilibrium. The experimental results are compared with previous data obtained with the same method, with the transient-hot-wire technique. and also with calculated values of thermal dilhusivity from reference data for thermal conductivity, heat capacity, and density. They demonstrate an agreement of 2.5%. which is within the uncertainty of the reference data.Paper presented at the Twelllh Symposium on Thermophysical Properties. June 19–24. 1994, Boulder, Colorado. U.S.A.Author to whom correspondence should be addressed.     

Thermal Conductivity of Carbon Dioxide–Methane Mixtures at Temperatures Between 300 and 425 K and at Pressures up to 12 MPa

The thermal conductivities of carbon dioxide and three mixtures of carbon dioxide and methane at six nominal temperatures between 300 and 425 K have been measured as a function of pressure up to 12 MPa. The measurements were made with a transient hot-wire apparatus. The relative uncertainty of the reported thermal conductivities at a 95% confidence level is estimated to be ±1.2%. Results of the low-density analysis of the obtained data were used to test expressions for predicting the thermal conductivity of nonpolar mixtures in a dilute-gas limit developed by Schreiber, Vesovic, and Wakeham. The scheme was found to underestimate the experimental thermal conductivity with deviations not exceeding 5%. The dependence of the thermal conductivity on density was used to test the predictive scheme for the thermal conductivity of gas mixtures under pressure suggested by Mason et al. and improved by Vesovic and Wakeham. Comparisons reveal a pronounced critical enhancement on isotherms at 300 and 325 K for mixtures with methane mole fractions of 0.25 and 0.50. For other states, comparisons of the experimental and predicted excess thermal conductivity contributions showed a smaller increase of the experimental data with deviations approaching 3% within the examined range of densities.     

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.     

Thermal conductivity of normal pentane in the temperature range 306–360 K at pressures up to 0.5 GPa

This paper reports the results of new, absolute measurements of the thermal conductivity of normal pentane in the temperature range 306 to 360 K at pressures up to 0.50 GPa. The experimental data have an estimated uncertainty of ±0.3%. The density dependence of the thermal conductivity along all of the isotherms cannot be represented by a common equation within its estimated uncertainty. Nevertheless, such a universal equation does provide a simple method of correlating the complete set of data with an error of no more than ±2.5%.     

Thermal Conductivity Enhancement in Aqueous Suspensions of Carbon Multi-Walled and Double-Walled Nanotubes in the Presence of Two Different Dispersants

Carbon multi-walled nanotubes (C-MWNTs) and alternatively carbon double-walled nanotubes (C-DWNTs) were added in water, following our previous work, in order to enhance the thermal conductivity of this traditional heat transfer fluid. Hexadecyltrimethyl ammonium bromide (CTAB) and Nanosperse AQ were employed as dispersants. The transient hot-wire technique was used for the measurement of the thermal conductivity with an instrument built for this purpose. The absolute uncertainty is better than 2%. The maximum thermal conductivity enhancement obtained was 34% for a 0.6% volume C-MWNT suspension in water with CTAB. All measurements were made at ambient temperature. In an attempt to evaluate and explain the experimental results, information about the microstructure of the suspensions is needed. The findings of these investigations are presented here along with the analysis.     

Thermal conductivity of toluene in the temperature range 35–90°C at pressures up to 600 MPa

New, absolute measurements of the thermal conductivity of liquid toluene are reported. The measurements extend over the temperature range 35–90°C and the pressure range 0.8–600 MPa. A new analytic evaluation of the contribution of radiation in an absorbing emitting fluid to the measurement process is presented. This analysis indicates that the thermal conductivity determined in a transient hot-wire instrument is the radiation-free value. As a consequence it is possible to assert that the overall uncertainty in the experimental data is one of ± 0.3%. A comparison of the data with the results of independent measurements by the same technique shows that the various sets of data are consistent within their mutual uncertainty.     

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%.     

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 of benzene and toluene

The thermal conductivity of liquid toluene and benzene was measured in the temperature range 298 to 370 K, near the saturation line, using an absolute transient hot-wire technique. The measurements were made in a modified version of an existing instrument, equipped with a new automatic Wheatstone bridge, computer controlled. The bridge measures the time that the resistance of a 7-m-diameter platinum wire takes to reach predetermined values, programmed by the computer. The computer can generate up to 1024 analog voltages, via a 12-bit D/A converter. The accuracy of the measurements with this new arrangement was assessed by measuring the thermal conductivity of a primary standard, toluene, at several temperatures and was found to be of the order of 0.3%. Benzene was chosen because it is under study as a possible secondary standard for liquid thermal conductivity by the Subcommittee on Transport Properties of IUPAC.Paper presented at the Tenth Symposium on Thermophysical Properties, June 20–23, 1988, Gaithersburg, Maryland, U.S.A.     

The thermal conductivity of n-hexadecane+ ethanol and n-decane+butanol mixtures

New absolute measurements, by the transient hot-wire technique, of the thermal conductivity of n-hexadecane and binary mixtures of n-hexadecane with ethanol and n-decane with butanol are presented. The temperature range examined was 295–345 K and the pressure atmospheric. The concentrations of the mixtures studied were 92% (by weight) of n-hexadecane and 30 and 70% (by weight) of n-decane. 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.