A transient hot-wire apparatus was used to measure the thermal conductivity of argon with both steady-state and transient methods. The effects of wire diameter, eccentricity of the wire in the cavity, axial conduction, and natural convection were accounted for in the analysis of the steady-state measurements. Based on measurements on argon, the relative uncertainty at the 95 % level of confidence of the new steady-state measurements is 2 % at low densities. Using the same hot wires, the relative uncertainty of the transient measurements is 1 % at the 95 % level of confidence. This is the first report of thermal conductivity measurements made by two different methods in the same apparatus. The steady-state method is shown to complement normal transient measurements at low densities, particularly for fluids where the thermophysical properties at low densities are not known with high accuracy.

The Cryogenics Division of the National Bureau of Standards is completing a ten-year experimental program on the properties of compressed gaseous and liquid parahydrogen. During the course of this program measurements have been made of PVT, specific heat, sound velocity, dielectric constant, refractive index, and viscosity coefficient at temperatures between 14 and 100°K and at pressures to 35 MN/m2. The thermal conductivity apparatus was designed by R. L. Powell and W. J. Hall H. M. Roder tested the apparatus by making several hundred thermal conductivity measurements on 4He gas, at temperatures between 20 and 282°K at pressures to 5 MN/m2 [1]. Helium was chosen because of its simple structure and because thermal conductivity and viscosity measurements in the temperature and pressure range of interest had been published previously. In 1968 several further improvements on the apparatus were made and 250 new measurements on the gaseous and liquid phases of normal and parahydrogen are now available. These measurements were made at temperatures between 17 and 200°K at pressures up to 10 MN/m2.

TAB II computer program provides values of thermodynamic and transport properties of hydrogen in useful format. Also, provides values for equilibrium hydrogen and para-hydrogen. Program fast, moderately accurate, and operates over wide ranges of input variables. Written in FORTRAN 77.

This paper presents new absolute measurements of the thermal conductivity and the thermal diffusivity of nitrogen made with a transient hot wire instrument. The instrument measures the thermal conductivity with an uncertainty less than +/- 1% and the thermal diffusivity with an uncertainty of +/- 5% except at the fluid critical point. The data cover the region from 80 to 300 K at pressures to 70 MPa. The data consist of 8 supercritical isotherms, 3 vapor isotherms, and 4 liquid isotherms.A surface fit is developed for our nitrogen thermal conductivity data from 80 to 300 K at pressures to 70 MPa. The data are compared with a recent theory for the first density coefficient of thermal conductivity and a new mode-coupling theory for the thermal conductivity critical enhancement. These data illustrate that it is necessary to study a fluid over a wide range of temperatures and densities in order to characterize the thermal conductivity surface.Isobaric heat capacity results were determined from the simultaneously measured values of thermal conductivity and thermal diffusivity, using the density calculated from an equation of state. The heat capacities obtained by this technique are compared to the heat capacities predicted by a recent equation of state developed specifically for nitrogen.

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.

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, Cp, of the fluid, provided that the density is measured, or available through an equation of state.

This paper presents a fresh analysis of the thermal conductivity surface of argon at temperatures between 100 and 325 K with pressures up to 70 MPa. The new analysis is justified for several reasons. First, we discovered an error in the compression-work correction, which is applied when calculating thermal conductivity and thermal diffusivity obtained with the transient hot-wire technique. The effect of the error is limited to low densities, i.e., for argon below 5 mol·L−1. The error in question centers on the volume of fluid exposed to compression work. Once corrected, the low-density data agree very well with the available theory for both dilute-gas thermal conductivity and the first density coefficient of thermal conductivity. Further, the corrected low-density data, if used in conjunction with our previously reported data for the liquid and supercritical dense-gas phases, allow us to represent the thermal conductivity in the critical region with a recently developed mode-coupling theory. Thus the new surface incorporates theoretically based expressions for the dilute-gas thermal conductivity, the first density coefficient, and the critical enhancement. The new surface exhibits a significant reduction in overall error compared to our previous surface which was entirely empirical. The uncertainty in the new thermal conductivity surface is ±2.2% at the 95% confidence level.

This paper presents new absolute measurements of the thermal conductivity and of the thermal diffusivity of gaseous argon obtained with a transient hot-wire instrument. We measured seven isotherms in the supercritical dense gas at temperatures between 157 and 324 K with pressures up to 70 MPa and densities up to 32 mol · L−1 and five isotherms in the vapor at temperatures between 103 and 142 K with pressures up to the saturation vapor pressure. The instrument is capable of measuring the thermal conductivity with an accuracy better than 1% and thermal diffusivity with an accuracy better than 5%. Heat capacity results were determined from the simultaneously measured values of thermal conductivity and thermal diffusivity and from the density calculated from measured values of pressure and temperature from an equation of state. The heat capacities presented in this paper, with a nominal accuracy of 5%, prove that heat capacity data can be obtained successfully with the transient hot wire technique over a wide range of fluid states. The technique will be invaluable when applied to fluids which lack specific heat data or an adequate equation of state.

The resistance of metals is a function of applied pressure, and this dependence is large enough to be significant in the calibration of transient hot-wire thermal conductivity instruments. We recommend that for the highest possible accuracy, the instrument's hot wires should be calibrated in situ. If this is not possible, we recommend that a value of γ, the relative resistance change with pressure, of -2×10-5 MPa-1 be used to account for the pressure dependence of the platinum wire's resistance.

The theory of the transient hot-wire technique for thermal conductivity measurements is reassessed in the special context of thermal diffusivity measurements. A careful examination of the working equation and an error analysis are employed to identify the principal sources of error. Notwithstanding earlier claims to the contrary, the best precision that can be attained in thermal diffusivity measurements is of the order of ±3%, while the accuracy is inevitably poorer. Experimental evidence is adduced from two different instruments that supports the analysis given here. Although the technique cannot yield values of the thermal diffusivity, k, as accurate as can be achieved by the use of the best possible individual values of λ,ρ, and Cp in the relation k=λ/ρCp, the simplicity of the technique makes it attractive for many purposes. It is even possible to derive values of the isobaric heat capacity Cp for many fluids not available from other methods.

The thermal conductivity of liquid argon has been measured along isotherms at 107, 113, 118, 124 and 130 K and pressures up to 10 MPa using the transient hot-wire technique. The instrument is capable of measuring the thermal conductivity of fluids with an accuracy of ±0.5 percent in thermodynamic states far from the critical region.

This Paper is a status report for viscosity and thermal conductivity data and correlations for pure fluids and fluid mixtures encountered in cryogenic process technology. Recommended correlations or tables of values are identified for each fluid. Specific data needs for future work are reported. Also presented are brief descriptions of the experimental techniques for viscosity and thermal conductivity measurements along with estimates of the associated experimental uncertainties.

The paper presents new experimental measurements of the thermal conductivity of liquid argon for four temperatures between 110 and 140 K with pressures to 70 MPa and densities between 23 and 36 mol · L−1. The measurements were made with a transient hot-wire apparatus. A curve fit of each isotherm allows comparison of the present results to those of others and to correlations. The results are sufficiently detailed to illustrate several features of the liquid thermal conductivity surface, for example, the dependence of its curvature on density and temperature. If these details are taken into account, the comparisons show the accuracy of the present results to be 1 %. The present results, along with several other sets of data, are recommended for selection as standard thermal conductivity data along the saturated liquid line of argon, extending the standards into the cryogenic temperature range. The results cover a fairly wide range of densities, and we find that a hard-sphere model cannot represent the data within the estimated experimental accuracy.

A correlation is presented for the extensive series of thermal conductivity measurements of binary methane-ethane mixtures. The composition dependences of the thermal conductivity in the dilute-gas region, dense-gas and liquid region, and critical region are discussed. The average absolute percentage deviation of the thermal conductivity surface as a function of temperature, density, and composition, from the experimental data, is 1.60%.

We report here the first thermal diffusivity measurements that cover a wide range of thermodynamic states including the dilute gas, the dense gas, the compressed liquid, and conditions close to the critical point. The heat capacity is obtained from simultaneous measurements of thermal conductivity and thermal diffusivity in a transient hot wire instrument, while the density is obtained from an equation of state. Values for the heat capacity, Cp, of argon were obtained at two temperatures, 172 and 275 K, with pressures up to 70 MPa. For these temperatures the densities range from that of the dilute gas to 2.2 times critical density while the heat capacity varies by a factor of seven from the dilute gas value.

We report here the first thermal diffusivity measurements that cover a wide range of thermodynamic states including the dilute gas, the dense gas, the compressed liquid, and conditions close to the critical point. The heat capacity is obtained from simultaneous measurements of thermal conductivity and thermal diffusivity in a transient hot wire instrument, while the density is obtained from an equation of state. Values for the heat capacity, C p , of argon were obtained at two temperatures, 172 and 275 K, with pressures up to 70 MPa. For these temperatures the densities range from that of the dilute gas to 2.2 times critical density while the heat capacity varies by a factor of seven from the dilute gas value.

Mesures dans les conditions indiquees et comparaison aux resultats experimentaux disponibles

The paper presents new measurements on the thermal conductivity of three methane-ethane mixtures with methane mole fractions of 0.69, 0.50, and 0.35. The thermal conductivity surface for each mixture is defined by up to 13 isotherms at temperatures between 140 and 330 K with pressures up to 70 MPa and densities up to 25 mol · L−1. The measurements were made with a transient hot-wire apparatus. They cover a wide range of physical states including the dilute gas, the single-phase fluid at temperatures above the maxcondentherm, the compressed liquid states, and the vapor at temperatures below the maxcondentherm. The results show an enhancement in the thermal conductivity in the single-phase fluid down to the maxcondentherm temperature, as well as in the vapor and in the compressed liquid. A curve fit of the thermal conductivity surface is developed separately for each mixture.