M. Dix

An apparatus to measure the thermal conductivity of liquids

The paper describes an apparatus for the measurement of the thermal conductivity of non-conducting liquids under their saturation vapour pressure. The instrument, which is based upon the transient hot wire principle, has been designed so that the measuring element conforms as closely as possible to an infinite line source of heat in an infinite fluid. Under these conditions the thermal conductivity of the liquid can be determined from the slope of a plot of the temperature rise of the heating element against the logarithm of time. The measurement system has been arranged so as to provide as many as 60 points on this plot for any particular thermodynamic state of the fluid under investigation. The reproducibility of the instrument is of the order of 0.03% and the precision of the measurements is estimated as +or-0.1%. Owing to a lack of a suitable theory for the effects of radiative heat transfer, the accuracy of the thermal conductivity values cannot be defined unequivocally, but a reasoned upper bound is +or-0.3%. Preliminary results are presented for n-heptane at three temperatures in the range 20 to 30 degrees C.

Application of the transient hot-wire technique to the measurement of the thermal conductivity of solids

A novel application of the transient hot-wire technique for thermal conductivity measurements is described. The new application is intended to provide an accurate means of implementation of the method to the determination of the thermal conductivity of solids exemplified by a standard reference ceramic material. The methodology makes use of a soft-solid material between the hot wires of the technique and the solid of interest. Measurements of the transient temperature rise of the wires in response to an electrical heating step in the wires over a period of 20 μs to 10 s allows an absolute determination of the thermal conductivity of the solid. The method is based on a full theoretical model with equations solved by finite-element method applied to the exact geometry. The uncertainty achieved for the thermal conductivity is better than ±1%, and for the product (ρCp) about ±3%. The whole measurement involves a temperature rise less than 4 K.

An absolute vibrating-wire viscometer for liquids at high pressures

The design and operation of a new vibrating-wire viscometer for the measurement of the viscosity of liquids at pressures up to 100 MPa are described. The design of the instrument is based on a complete theory so that it is possible to make absolute measurements with an associated error of only a few parts in one thousand. Absolute measurements of the viscosity of n-hexane are reported at 298.15 K at pressures up to 80 MPa. The overall uncertainty in the reported viscosity data is estimated to be ±0.5%, an estimate confirmed by the comparison of values of viscosity of slightly inferior accuracy.

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%.

Absolute determination of the thermal conductivity of the noble gases and two of their binary mixtures as a function of density

The paper reports absolute measurement of the thermal conductivity of the monatomic gases helium, neon, argon, krypton and xenon and of binary mixtures of helium and neon and argon and krypton. The measurements have been carried out in a transient hot-wire apparatus at 35 °C and in the pressure range 0.5–10 MPa. The overall uncetainty in the reported thermal conductivity data is estimated to be ±0.2%, an estimate which is confirmed by a comparison with low density viscosities for the same gases.The experimental thermal conductivity for each system studied conforms to a polynomial expansion in density. It is found that the data for the binary mixtures in the limit of zero density can only be adequately represented if third-order kinetic theory expressions are employed. A recently proposed scheme for the evaluation of the thermal conductivity of dense gas mixtures is found to represent the data for argon + krypton adequately. However, for helium + neon mixtures the proposed scheme required modifications in order to provide a satisfactory description of the experimental data.

A vibrating-wire densimeter for measurements in fluids at high pressures

The paper describes a new type of densimeter especially designed for the accurate measurement of fluid densities at pressures up to 400 MPa. The densimeter makes use of the buoyancy force exerted on a mass immersed in the test fluid to alter the resonant frequency of a thin wire from which the mass is suspended. The resonant frequency of the wire carrying the mass is related to the fluid density by means of working equations which are based on a complete analysis of the fluid motion around the wire. Preliminary results are presented for n-octane at pressures up to about 100 MPa near ambient temperature. The results show that the instrument has a precision of ±0.1 % in density at elevated pressures when evaluated on a relative basis, while the accuracy is estimated to be one of ±0.2%.

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%.

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.

Thermal conductivity of chlorobenzene at pressures up to 430 MPa

New, absolute measurements of the thermal conductivity of the moderately polar liquid, chlorobenzene, are reported for four isotherms in the temperature range 308–360 K for pressures up to 430 MPa. The results have an estimated accuracy of ±0.3%.

Vapor-phase thermal conductivity measurements of refrigerants

The paper reports further developments of the transient hot-wire technique. The particular development of interest is the extension of the technique to study polar, or electrically-conducting gases with a relatively low thermal conductivity but a high thermal diffusivity, circumstances which occur at low density and therefore low pressure, for gases of high molecular weight. The theory of the transient hot-wire instrument is examined again in order to guide a revised design of the thermal conductivity cell with this particular application in mind. Test measurements have then been conducted on helium, argon, and propane at low and moderate pressures to confirm that the instrument operates in accordance with the theory of it. The satisfactory completion of these tests demonstrates that the new equipment overcomes many of the defects observed in earlier variants of the instrument for application to the study of refrigerant gases.