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.     

Absolute measurements of the thermal conductivity of mixtures of alcohols with water

New absolute measurements of the thermal conductivity of mixtures of methanol, ethanol, and propanol with water are presented. The measurements were performed in a tantalum-type transient hot-wire instrument at atmospheric pressure, in the temperature range 300–345 K. The overall uncertainty of the reported values is estimated to be less than ±0.5%, an estimate confirmed by measurements of the thermal conductivity of water. The mixtures with water studied have compositions of 25. 50, and 75%, by weight, of methanol and ethanol and 50%, by weight, of propanol. A recently proposed semiempirical scheme for the prediction of the thermal conductivity of pure liquids is extended to allow the prediction of the thermal conductivity of these mixtures from the pure components, as a function of both composition and temperature.     

The thermal conductivity of n-hexane,n-heptane,and n-decane by the transient hot-wire method

New absolute measurements of the thermal conductivity of liquid n-hexane, n-heptane, and n-decane are reported. The measurements have been carried out in the temperature range 300–370 K at atmospheric pressure in a transient hotwire instrument. The accuracy of the measurements is estimated to be ±0.5%. The density dependence of the thermal conductivity of n-hexane and n-heptane is found to be well described by a universal equation for the hydrocarbons based on a rough hard-sphere model. The measurements of the three hydrocarbons studied are also employed to generate more accurate effective core volumes, which are the only parameters characteristic of the fluid required for the application of the proposed universal scheme.     

Absolute measurements of the thermal conductivity of mixtures of alkene-glycols with water

New absolute measurements of the thermal conductivity of ethylene and propylene glycol and their mixtures with water are presented. The measurements were performed in a tantalum-type transient hot-wire instrument at atmospheric pressure, in the temperature range 295–360 K. The overall uncertainty of the reported values is estimated to be less than ±0.5%, an estimate confirmed by measurements of the thermal conductivity of water. The mixtures with water studied have compositions of 25, 50, and 75%, by weight. A recently proposed semiempirical scheme for the prediction of the thermal conductivity of pure liquids is extended to allow the prediction of the thermal conductivity of these mixtures from the pure components, as a function of both composition and temperature.     

Simultaneous measurement of the thermal conductivity and thermal diffusivity of liquids

In theory, the hot-wire technique for measuring the thermal conductivity of liquids can be used simultaneously to determine the thermal diffusivity. In practice, however, the latter property has so far been determined only with moderate accuracy because of (a) inaccurate bridge balancing due to drift problems, (b) parasitic capacities that delay the heating, and (c) poor precision in the determination of the time. A new measurement procedure has been developed which features (a) a short measuring time, (b) a reduced significance of the balancing technique, (c) a good reproducibility, and (d) a low sensitivity to most error sources. Thermal conductivity and thermal diffusivity results using this procedure, for toluene and n-heptane, which are the generally accepted standards for thermal conductivity, are presented and compared with results from other sources.     

Viscosity and thermal conductivity of binary n-heptane + n-alkane mixtures

New absolute measurements of the viscosity of binary mixtures of n-heptane with n-hexane and n-nonane are presented. The measurements, performed in a vibrating-wire instrument, cover a temperature range 290–335 K and pressures up to 75 MPa. The concentrations studied are 40 and 70% by weight of n-heptane. The accuracy of the reported viscosity data is estimated to be ±0.5%. The present measurements, together with other n-heptane + n-alkane viscosity and thermal-conductivity measurements, are used to develop a consistent semiempirical scheme for the correlation and prediction of these mixture properties from those of the pure components.     

Absolute measurement of the thermal conductivity of propylene carbonate by the AC transient hot-wire technique

The paper describes a new apparatus for measuring the thermal conductivity of liquids based on a transient hot-wire method. The apparatus has been used to measure the thermal conductivity of propylene carbonate (C₄H₆O₃). The measurements have been carried out in the temperature range 284–313 K and at saturation pressure. The accuracy of the data is within ±1.5%.     

The thermal conductivity and viscosity of acetic acid-water mixtures

The viscosity and thermal conductivity of acetic acid water mixtures were measured over the entire composition range and at temperatures ranging from 293 to 453 K. Viscosity measurements were performed with a high-pressure viscometer and thermal conductivity was measured using a modified transient hot-wire technique. A mercury filled. glass capillary was used as the insulated hot wire in the measurements. The l iscosity data showed unusual trends with respect to composition. At it given temperature. the viscosity was seen to increase with increasing acid concentration, attain a maximum. and then decrease. The thermal conductivity, on the other hand, decreased monotonically with acid concentration. A generalized corresponding-states principle using water and acetic acid as the reference fluids was used to predict both viscosity and thermal conductivity with considerable sucres.Paper presented at the Twelfth Symposium on Thermophysical Properties, June 19–34, 1994, Boulder. Colorado, U.S.A.     

Absolute measurements of the thermal conductivity of alcohols by the transient hot-wire technique

New absolute measurements of the thermal conductivity of methanol, ethanol, propanol, butanol, pentanol, and hexanol at atmospheric pressure and in the temperature range 290–350 K are reported. The overall uncertainty in the reported thermal conductivity data is estimated to be better than ±0.5%, an estimate confirmed by the measurement of the thermal conductivity of water. The measurements presented in this paper have been used to develop a consistent theoretically based correlation for the prediction of the thermal conductivity of alcohols. The proposed scheme, based on an extention of the rigid-sphere model, permits the density dependence of the thermal conductivity of alcohols, for temperatures between 290 and 350 K and atmospheric pressure, to be represented successfully by an equation containing just one parameter characteristic of the fluid at each temperature.Paper presented at the Tenth Symposium on Thermophysical Properties, June 20–23, 1988, Gaithersburg, Maryland, U.S.A.     

Accurate measurement of the thermal conductivity and thermal diffusivity of toluene andn-heptane

Accurate and simultaneous measurements of the thermal conductivity and thermal diffusivity of toluene andn-heptane were made with an improved transient hot-wire method by using a transfer function having a feedback loop, in the temperature range of 0 to 45°C at atmospheric pressure. The accuracy of the empirical equations as a function of temperature is estimated to be 0.4 to 0.5% for the thermal conductivity and about 4% for the thermal diffusivity. Paper presented at the Fourth Asian Thermophysical Properties Conference, September 5–8, 1995, Tokyo, Japan.     

瞬态热线法液体导热系数测试系统的研制

根据瞬态热线法测量导热系数的原理,研制了测量装置和数据采集系统.利用阳极氧化的方式,在热线表面进行绝缘处理,使其能够适用于导电性或者极性物质的导热系数的研究.为了检验该系统的性能,在常温常压下对蒸馏水的导热系数进行了测量.测试结果表明,该系统能够满足导热系数测试的需要.     

A computer-controlled instrument for the measurement of the thermal conductivity of liquids

A new instrument for the measurement of the thermal conductivity of liquids by the transient hot-wire method is described. The instrument has features in common with earlier versions but employs a novel technique for the determination of the transient temperature rise of the hot wire during the course of a measurement. New determinations of the thermal conductivity of toluene confirm the accuracy of the instrument to be better than 0.5%.     

Simultaneous measurement of thermal conductivity and thermal diffusivity of solids by the parallel-wire method

An improved parallel-wire technique for simultaneous measurement of thermal conductivity and thermal diffusivity is presented. The deviation between experimental results and recommended (or another author's) values is less than 5% for fused quartz and refractory brick.     

The thermal conductivity and viscosity of benzene

New absolute measurements of the thermal conductivity of liquid benzene are reported. The measurements have been carried out in the temperature range 295–340 K, at atmospheric pressure, in a transient hot-wire instrument. The accuracy of the measurements is estimated to be ±0.5%. The measurements presented in this paper have been used, in conjunction with other high-pressure measurements of thermal conductivity and viscosity, to develop a consistent theoretically based correlation for the prediction of these properties. The proposed scheme permits the density dependence of the thermal conductivity and viscosity of benzene, for temperatures between 295 and 375 K and pressures up to 400 MPa, to be represented successfully by two equations containing just two parameters characteristic of the fluid at each temperature.     

Thermal conductivity of water and 2-n-butoxyethanol and their mixtures in the temperature range 305–350 K at pressures up to 150 MPa

The thermal conductivity of binary liquid mixtures of water and 2-n-butoxyethanol has been measured within the temperature range 305–350 K at pressures up to 150 MPa. The measurements have been carried out with a transient hotwire instrument suitable for electrically conducting liquids and have an estimated accuracy of ±0.3%. The liquid mixture has a closed-loop solubility and reveals a lower critical solution temperature for a mole fraction of 2-n-butoxyethanol of 0.0478 at a temperature of 322.25 K. The results of the measurements reveal a small, but discernible, enhancement of the thermal conductivity of the solution at the critical composition.Paper presented at the Twelfth Symposium on Thermophysical Properties. June 19–24, 1994, Boulder, Colorado, U.S.A.     

Mutual diffusivity in binary mixtures of n-heptane with n-hexane isomers

This paper presents a study of the influence of branching in the binary diffusion coefficients of n-heptane + n-hexane isomers, in the liquid state. The measurements have been made with the Taylor dispersion technique, at several compositions, at 283 and 298 K, for the X + n-heptane mixtures, where X= n-hexane, 3-methylpentane, 2, 3-dimethylbutane, and 2, 2-dimethylbutane. The results show a very interesting behavior of the composition dependence of the binary diffusion coefficients, presenting a maximum, for compositions about a molar fraction of n-heptane of 0.5, which increases with the increase in the degree of branching, suggesting the possibility of order-disorder effects caused by stereochemically favored packing in the liquid phase and energetically favored segment interaction in the liquid mixtures. An attempt to apply the van der Waals model to these data could not predict the experimental binary diffusion coefficients of these systems within the experimental accuracy.Paper presented at the Tenth Symposium on Thermophysical Properties, June 20–23, 1988, Gaithersburg, Maryland, U.S.A.     

Radiative heat transfer in transient hot-wire measurements of thermal conductivity

New measurements of the thermal conductivity of liquid toluene between 300 and 550 K have been used to study the importance of radiative heat transfer when using the transient hot-wire technique. The experimental data were used to obtain the radiation correction to the hot-wire temperature rises. Radiationcorrected values of thermal conductivity are reported. This study shows that the transient hot-wire method is much less affected by radiation than steady-state techniques.     

The thermal conductivity of toluene and water

A new instrument is presented to measure the thermal conductivity of polar and electrically conducting liquids based on the transient coated hot-wire method. The performance of the apparatus has been assessed with toluene and water, which are recognized as standard reference materials for nonpolar and polar fluids, respectively. New results are reported fort the thermal conductivity of these liquids between 298 and 370 K and at pressures slightly above the saturation. The results show that the instrument is capable of an accuracy better than ±0.5%, while the precision and reproducibility are better than ±0.3%.     

The thermal conductivity of xylene isomers in the temperature range 290–360 K

New absolute measurements of the thermal conductivity of the three xylene isomers are reported. The measurements have been carried out in the temperature range 290–360 K, at atmospheric pressure, in a transient hot-wire instrument. The accuracy of the measurements is estimated to be ±0.5%. The measurements presented in this paper have been used in conjuction with our earlier reported measurements of liquid benzene and toluene, at atmospheric pressure, to develop a consistent theoretically based predictive scheme for the thermal conductivity of these five aromatic hydrocarbons. The proposed scheme, containing just one parameter characteristic of each fluid, permits the prediction of the thermal conductivity of the five aromatic hydrocarbons in the temperature range 290–360 K and at pressures up to 350 MPa, with an accuracy of ±2.5%.     

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.