L. Karagiannidis

The transient hot-wire technique : A numerical approach

The measurement of the thermal conductivity of a fluid by means of the transient hot-wire technique so far has made use of an analytical solution of the energy conservation equation for an ideal model, coupled with a set of approximate analytical corrections to account for small departures from the model. For this solution to be valid, constraints were always imposed on the experimental conditions and the construction of the apparatus, resulting in an inability to measure the thermal conductivity of high-thermal diffusivity fluids. In this paper, the set of energy conservation equations describing the transient hot-wire apparatus is solved using the numerical finite-element method. Because no approximate solutions are involved, this provides a much more general treatment of the heat transfer processes taking part in the real experiment, removing all the aforementioned constraints. In the case of the measurement of the thermal conductivity of liquids (fluids with low thermal-diffusivity values), the numerical solution fully agrees with the existing analytical solution. In the case of the measurement of the thermal conductivity of gases, the present solution allows the extension of the application of the transient hot-wire technique to experimental conditions where the value of the thermal diffusivity of the fluid is high.

Measurements of the thermal conductivity of liquid R32, R124, R125, and R141b

This paper reports measurements of the thermal conductivity of refrigerants R32, R124, R125, and R141b in the liquid phase. The measurements, covering a temperature range from 253 to 334 K and pressure up to 20 MPa, have been performed in a transient hotwire instrument employing two anodized tantalum wires. The uncertainty of the present thermal-conductivity data is estimated to be ±0.5%. The experimental data have been represented by polynomial functions of temperature and pressure for the purposes of interpolation. A comparison with other recent measurements is also included.

Compression work using the transient hot-wire method

A new treatment of the effect of the work of compression upon thermal conductivity measurements by the transient hot-wire technique is presented. The new analysis improves upon those given earlier and leads to quite a different result. The result makes it clear that the dilute gaseous state need not be excluded from the range of thermodynamic states in which accurate measurements are made owing to this effect, in contrast to the conclusions of earlier work.

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.

Measurements of the Viscosity of New Refrigerants in the Temperature Range 270-340 K at Pressures up to 20 MPa ~

A recently modified vibrating-wire instrument was employed to measure the liquid viscosity of a wide selection of new refrigerants under pressure. Calibration of the viscometer with water over the range of measurements confirmed that the estimated uncertainty of the measurements is 0.5%, while the precision is 0.3%. With this instrument, the viscosity of chlorofuorocarbons (CFCs) and alternative refrigerants. R11. R12. R22, R32. R124, R125. 11134a. R 141 b, and R152a, was measured over the temperature range from 270 to 340 K, from just above the saturation pressure up to 211 M Pa. The experimental data, represented by polynomial functions of temperature and pressure, are used in a comparative examination of other recently reported experimental measurements of the viscosity of all these refrigerants. to investigate the uncertainty with which the viscosity is known.

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.

Toward Standard Reference Values for the Thermal Conductivity of High-Temperature Melts

The paper describes the progress made in the development of an instrument for the measurement of the thermal conductivity of molten materials at high temperatures. The instrument is designed to provide experimental data of unique accuracy at temperatures up to 1500 K on a wide range of materials, some of which will be suitable as standard reference substances. In particular, the paper concentrates upon the method of analysis of the experimental data and upon those critical aspects of the experimental technique which will enable a high accuracy to be achieved. Demonstrations of the validity of the method of treating one correction and of its behavior under typical conditions are included.

Measurements of the viscosity of n-heptane + n-undecane mixtures at pressures up to 75 MPa

New absolute measurements of the viscosity of binary mixtures of n-heptane and n-undecane are presented. The measurements, performed in a vibrating-wire instrument, cover the temperature range 295–335 K and pressures up to 75 MPa. The concentrations studied were 40 and 70%, by weight, of n-heptane. The overall uncertainty in the reported viscosity data is estimated to be ±0.5%. A recently extended semiempirical scheme for the prediction of the thermal conductivity of mixtures from the pure components is used to predict successfully both the thermal conductivity and the viscosity of these mixtures, as a function of composition, temperature, and pressure.

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%.

The thermal conductivity of some alkyl ethers and alkanones

New absolute measurements, by the transient hot-wire technique, of the thermal conductivity of some alkyl ethers and alkanones are presented. The alkyl ethers studied are tert-butyl methyl ether, di-iso-propyl ether and di-butyl ether, while the alkanones studied are 2-butanone, 4-methyl pentan-2-one, and 2-octanone. The temperature range examined was 295–350 K, and the pressure atmospheric. The overall uncertainty in the reported thermal conductivity data is estimated to be better than ±1%, an estimate confirmed by the measurement of the thermal conductivity of water.