Showing papers in "International Journal of Thermophysics in 1987"

Scattering of Phonons by Vacancies

Abstract: The scattering of phonons by vacancies is estimated by a perturbation technique in terms of the missing mass and the missing linkages. An argument is given why distortion effects can be disregarded. The resonance frequency of the defect is sufficiently high so that resonance effects can be disregarded for phonons in the important frequency range for thermal conduction. The theory is applied to the thermal resistance by vacancies in cases where the vacancy concentration is known: potassium chloride with divalent cations, nonstoichiometric zirconium carbide, and tin telluride.

Volumetric behavior of pure alcohols and their water mixtures under high pressure

Abstract: The specific volumes of C1-C4 alcohols and binary mixtures of water with methanol, ethanol, 1-propanol, 2-propanol, and 2-methyl-2-propanol are presented as functions of temperature, pressure, and composition. The measurements were carried out using a modified Adams piezometer and a high-pressure burette method in a temperature range from 283.15 to 348.15 K at pressures up to 350 MPa. The uncertainties in the specific volume obtained are estimated to be less than 0.09%. The specific volumes of the pure alcohols and their mixtures with water are found to decrease monotonously with increasing pressure. The numerical P-V relations at each temperature and composition are correlated satisfactorily as a function of pressure by the Tait equation. Definite inflections appear on the isobars of isothermal compressibility or partial molar volume versus composition of alcohol + water mixtures.

Viscosity of (water + alcohol) mixtures under high pressure

Abstract: New experimental viscosity data are presented for aqueous solutions of methanol, ethanol, 1-propanol, 2-propanol, and 2-methyl-2-propanol (t-butyl alcohol) in the temperature range from 283 to 348 K and pressures up to 120 MPa. The viscosity measurements were performed using a falling-cylinder viscometer on a relative basis with an uncertainty of less than 2%. The viscosity of pure alcohols and aqueous solutions is found to increase almost linearly with increasing pressure, whereas that of water decreases slightly with pressure at temperatures below 298 K. As for the composition dependence of the viscosity, a distinct maximum appears near 0.3–0.4 mole fraction of alcohol on all isobars at each temperature. The viscosity maximum shifts gradually to a higher alcohol concentration with increasing temperature and pressure. The isobars of aqueous 2-propanol and 2-methyl-2-propanol solutions have another shallow minimum near 0.9 mole fraction of alcohol below 323 K. The experimental results were analized empirically by a Tait-type equation and a free-volume theory. It was found that the isothermal viscosity data were satisfactorily correlated by these equations as functions of pressure and composition or of density and composition.

The Vapor Pressure of Indium, Silver, Gallium, Copper, Tin and Gold between 0.1 and 3.0 Bar

Abstract: The vapor pressure of several liquid metals was measured using a method based on the gas-controlled heat pipe. Small samples of the test material were placed in a tungsten tube and heated to temperatures above 2900 K. The vapor pressure was measured using a gas-buffered pressure transducer and the vapor temperature was inferred from the tube surface temperature, which was measured with an optical pyrometer. Most of the tests were terminated by the failure of the containment tube. The measured pressures agree well with those calculated by thermodynamic methods from data at lower temperatures.

Thermal conductivity of Inconel 718 and 304 stainless steel

Abstract: The results of thermal conductivity measurements on Inconel 718 and 304 stainless steel by the comparative and flash diffusivity techniques are reported for the temperature range 0–700°C For 304 stainless steel, excellent agreement with published data is found for the specific heat, thermal diffusivity, and thermal conductivity In the case of Inconel 718, the measurements show that the conductivity depends critically on the sample thermal history and the metallurgical condition of the alloy Measurements on a solution-treated sample indicated a conductivity function close to that reported previously, while precipitated samples showed a higher conductivity, similar to the conductivityvs-temperature function used for reduction of comparative thermal conductivity data with Inconel 718 references These results indicate that Inconel 718 is not a suitable reference for high-accuracy comparative thermal conductivity measurements unless its thermal history and associated conductivity function are known

Critical evaluation of the thermodynamic properties of cobalt

Abstract: The thermodynamic properties and the pressure-temperature phase diagram of Co have been evaluated from experimental information using thermodynamic models for the Gibbs energy of the various phases. For hcp and fcc Co the model describes the magnetic contribution to the molar volume, expansivity, and compressibility and the efect of pressure upon the Curie temperature. Experimental data of many different types are satisfactorily described by the evaluated model parameters.

Thermodynamic properties of aluminum

Abstract: This work reviews and discusses the data on the thermodynamic properties of aluminum available through May 1984. However, two papers dated 1985 which are useful to this work are also included. These properties include heat capacity, enthalpy, enthalpy of transition and melting, vapor pressure, and enthalpy of vaporization. The recommended values for heat capacity cover the temperature range from 0.1 to 2800 K. The recommended values for enthalpy, entropy, Gibbs energy function, and vapor pressure cover the temperature range from 298.15 to 2800 K.

Thermodynamic properties of nickel

Abstract: This work reviews and discusses the data and information on the thermodynamic properties of nickel available through May 1984. These properties include heat capacity, enthalpy, enthalpy of transition and melting, vapor pressure, and enthalpy of vaporization. The recommended values for heat capacity cover the temperature range from 1 to 3200 K. The recommended values for enthalpy, entropy, Gibbs energy function, and vapor pressure cover the temperature range from 298.15 to 3200 K.

Densities of n-alkanes and their mixtures at elevated pressures

Abstract: Accurate density data for n-alkanes over a wide range of temperature and pressure have been used to test existing correlation and prediction methods. It is found that the most successful representation at temperatures up to 0.66 times the critical temperature and pressures up to 150 MPa is given by the Tait equation in the form (ρ−ρ0)/ρ=C log [(B + P)/(B + P0)], where subscript 0 refers to 0.101 MPa, with C equal to 0.2000, and [B+(Cn−6)], where Cn is the number of carbon atoms in the alkane chain, is a smooth function of reduced temperature. A simple extension of this method to mixtures gives an excellent prediction of densities at pressures up to 150 MPa over the same reduced temperature range.

Thermodynamic properties of titanium

Abstract: This work reviews and discusses the data and information on the thermodynamic properties of titanium available through May 1984. These properties include heat capacity, enthalpy, enthalpy of transition and melting, vapor pressure, and enthalpy of vaporization. The recommended values for heat capacity cover the temperature range from 1 to 3800 K. The recommended values for enthalpy, entropy, Gibbs energy function, and vapor pressure cover the temperature range from 298.15 to 3800 K.

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

Abstract: 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.

Thermal diffusivity of fluids in a broad region around the critical point

Abstract: Dynamic light scattering is a suitable method for the investigation of transport properties such as the thermal diffusivity of optically transparent fluids. The main advantages of the method are its quickness, the fact of the thermodynamic state of equilibrium of the sample (gradients are not required), and the relatively simple evaluation of data without the necessity of calibration. However, an insufficient production of intensity of scattered light may be a limiting effect. For that reason the vicinity of the gas-liquid critical point represents the classical range of application. In this paper, it is shown that by means of an appropriate choice of experimental apparatus, measurements are also feasible in an extended range of states. Broad regions around critical points of three pure fluids (sulfur hexafluoride, SF6; ethane, C2H6; nitrous oxide, N2O) over temperature ranges ¦T-Tc¦ of 0.02 to 50 K and density ranges (ρ/ρc) of 0.2 to 2 were investigated. In this region the thermal diffusivity shows great variations with temperature and density and cannot be described by means of ideal-gas behavior or relations for liquids. The measurements were carried out along the coexistence curve for both phases, along the critical isochore and along some isotherms with T≶Tc. The measured or calculated density, pressure, and thermal diffusivity data as well as some correlations are presented.

Statistical mechanical description of supercritical fluid extraction and retrograde condensation

Abstract: The phenomena of supercritical fluid extraction (SFE) and its reverse effect, which is known as retrograde condensation (RC), have found new and important applications in industrial separation of chemical compounds and recovery and processing of natural products and fossil fuels. Full-scale industrial utilization of SFE/RC processes requires knowledge about thermodynamic and transport characteristics of the asymmetric mixtures involved and the development of predictive modeling and correlation techniques for performance of the SFE/RC system under consideration. In this report, through the application of statistical mechanical techniques, the reasons for the lack of accuracy of existing predictive approaches are described and they are improved. It is demonstrated that these techniques also allow us to study the effect of mixed supercritical solvents on the solubility of heavy solutes (solids) at different compositions of the solvents, pressures, and temperatures. Fluid phase equilibrium algorithms based on the conformal solution van der Waals mixing rules and different equations of state are presented for the prediction of solubilities of heavy liquid in supercritical gases. It is shown that the Peng-Robinson equation of state based on conformal solution theory can predict solubilites of heavy liquid in supercritical gases more accurately than the van der Waals and Redlich-Kwong equations of state.

Viscosity of liquid toluene in the temperature range 25–75°C

Abstract: New accurate experimental data are presented for the viscosity of liquid toluene. The viscosity was measured relative to the viscosity of liquid water with the aid of an Ubbelohde capillary viscometer. The data cover a temperature range from approximately 25 to 75°C and are represented with high precision by an Arrhenius equation

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

Abstract: 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%.

Viscosities of nonelectrolyte liquid mixtures. I. n-hexadecane + n-octane

Abstract: Viscosities and densities of the n-alkanes, hexane, heptane, octane, nonane, decane, dodecane, tetradecane, hexadecane, and tetracosane, were measured for temperatures from 303 to 338 K. Viscosities were measured using a standard Utube Ostwald viscometer; a pycnometer was used to measure both pure alkane and mixture densities. Results for the binary system n-hexadecane + n-octane at 318.16, 328.16, and 338.16 K are presented here, and comparisons with selected correlating equations are made.

The thermal conductivity of liquid argon for temperatures between 110 and 140 K with pressures to 70 MPa

Abstract: 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.

Solid-liquid phase equilibria of benzene + cyclohexane system under high pressures

Abstract: Solid-liquid phase equilibria of the benzene + cyclohexane system have been investigated experimentally at temperatures from 278 to 323 K and pressures up to 500 MPa using a newly designed optical vessel. The uncertainties of the measurements of temperature, pressure, and composition are within ±0.1 K, ±0.5 MPa, and ±0.001 mole fraction, respectively. The solid-liquid equilibrium pressure at a constant composition increases almost linearly with increasin temperature. The eutectic point shifts to a higher temperature and to a benzenerich composition with increasing pressure. This trend is found to agree with the direction predicted by the van Laar equation. The solid-liquid coexistence curves can be expressed by the Wilson equation with a mean deviation of 0.007 and a maximum deviation of 0.029 in mole fraction.

Saturation vapor pressure and critical constants of H 2 O, D 2 O, T 2 O, and their isotopic mixtures

Abstract: Reliable data on the vapor pressure and critical constants of H2O isotopes and their isotopic mixtures are required for the generation of thermophysical properties data over a wide range of temperatures and pressures. In this study, vapor pressure equations for D2O and T2O have been developed based on the latest experimental and theoretical information. Considering the similarity among H2O isotopes, the functional form of the Saul and Wagner equation, fully proven for H2O, has been employed. The present equation for D2O shows a lower trend by up to 0.09% than the widely used Hill and MacMillan equation at temperatures below 150°C. For the vapor pressure of the isotopic mixtures, the available experimental data have been examined for the validity of Raoult's law. Then it has been shown that the critical temperature and the critical pressure of the isotopic mixture can also be predicted as simple mole-fraction average values.

Thermal conductivity of normal pentane in the temperature range 306-360 K at pressures up to 0. 5 GPa

Abstract: 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%.

Measurement of infrared absorption of some oxides in connection with the radiative transfer in porous and fibrous materials

Abstract: The radiative heat transfer in porous and fibrous materials depends on the infrared absorption and scattering properties of the materials. The infrared absorption can be obtained by transmission measurements in single crystals. It is shown in the case of Al2O3, and MgO that the analysis of absorption data as a function of temperature gives the possibility of decomposing the lattice absorption coefficient in its different multiphonon contributions. The study of multiphonon components is necessary to understand as well as to predict the frequency and temperature behavior of the lattice absorption in materials. Measurements performed on TiO2 and ZrO2 also are reported; it is observed that electronic effects considerably enhance the absorption level at high temperatures. From diffuse reflection measurements on a scattering sample, the ratio of absorption and scattering can be obtained. So experimental data can be used to calculate the radiant flux. Several models have been proposed, based on isotropic and anisotropic approximations. They involve the absorption coefficient σa, the scattering coefficient σs, the backscattered fraction factor b, and a phase function parameter a 1. Due to the approximations on which the models are based, the calculated values of the radiant heat flux show large differences (as large as 30%), whatever the accuracy of the values of optical parameters which are used. It appears worthy to use the experimental data on σa and σs, which can be obtained from transmission and diffuse reflection measurements.

Simultaneous measurement of the thermal conductivity and thermal diffusivity of liquids

Abstract: 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.

Determination of the interaction second virial coefficients for the carbon dioxide-ethane system from refractive index measurements

Abstract: The compressibility behavior of the CO2-C2H6 system was investigated experimentally. In this work, the refractive indexes of the pure gases and the mixtures were measured using an optical apparatus. On the basis of these data, density and compressibility factors were computed using the Lorentz-Lorenz law. For the pure components, carbon dioxide and ethane, the data from the optical system were slightly adjusted by a fit to Burnett apparatus data measured separately. The experiments produced very accurate virial coefficients and refraction virial coefficients. This paper reports on the effect of temperature on the second and third virial coefficients. For the first refraction virial coefficient, no influence of temperature was found with the equipment used. The interaction second virial coefficient B 12 (as a function of temperature) was computed from experimental data for the CO2-C2H6 binary system. The data, for which an accuracy of ±1.5 cm3 · mol−1 was estimated, are in agreement with the data published by Holste et al.

The thermal conductivity of gases: Incorrect results due to desorbed air

Abstract: Air desorbed from the measuring instrument can falsify the thermal conductivity of a gas measured by steady-state methods. For a guarded hot-plate apparatus the contamination effect was determined to depend on both the residence time in the system and the temperature. The investigation covered the gases H2, He, Ne, CH4, N2, air, Ar, and Kr. For gases whose conductivity is better than that of air (H2, He) the measured values are too small, and for gases of poorer conductivity they are too high. Corrections for the effect of impurity have been applied to the measurements presented. These impurity corrections are considerably larger than the precision of the measurements, but they are of the order of the estimated overall uncertainty of the measurements. The departures between the corrected thermal conductivities reported here and values taken from the correlations in the literature run up to 5 % at the highest temperatures.

Solid-liquid phase equilibria of (α-methylnaphthalene + β-methylnaphthalene) and (chlorobenzene + bromobenzene) systems under high Pressures

Abstract: Solid-liquid phase equilibria of the (α-methylnaphthalene + β-methylnaphthalene) and the (chlorobenzene + bromobenzene) systems have been investigated at temperatures from 278 to 343 K and pressures up to 500 MPa using a high-pressure optical vessel. The uncertainties of the measurements of temperature, pressure, and composition were within ±0.1 K, ±0.5 MPa, and ±0.001 mole fraction, respectively. In both systems, the freezing and melting pressures at a constant composition increase almost linearly with increasing temperatures. In the former system, where the two components can form a solid solution with one another to a limit extent, the eutectic point shifts to a higher temperature and to a α-methylnaphthalene-rich composition with increasing pressures. In the latter system, where the two components are completely soluble in each other in the solid phase, the freezing points of all mixtures lie between those of the pure components at each pressure. It is found that the coexistence curves obtained can be expressed by a quadratic equation in pressure.

The thermal conductivity surface for mixtures of methane and ethane

Abstract: 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%.

Thermodynamic properties and vapor pressures of polar fluids from a four-parameter corresponding-states method

Abstract: A recently proposed extended Lee-Kesler corresponding-states method (ELK) for polar fluids which accurately predicts compressibility factors and departure functions is considered. Tables of polar deviation functions have been generated and values of the shape/size and polar parameters for 52 polar fluids have been calculated, allowing the method to be used for quick hand calculations in addition to the previous, more accurate, computer applications. Additionally, vapor pressures of 44 pure polar fluids were computed using the full version of the ELK and the equality of the Gibbs free energy criterion for phase equilibrium. An ELK vapor pressure correlation is proposed which is essentially numerically equivalent to, but computationally simpler than, the former method. Computed vapor pressures agree with experimental values as well or better than other vapor pressure equations designed exclusively for vapor pressure prediction of polar fluids.

Thermal conductivity of steam from 250 to 510°C at pressures up to 95 MPa including the critical region

Abstract: New measurements of the thermal conductivity of steam have been performed in the temperature range 250–510°C and in the pressure range from 1 up to 95 MPa. Most of the measurements were taken at temperatures greater than the critical temperature, where the enhancement of the thermal conductivity is observed. The experimental values are compared to the IAPS formulation for the thermal conductivity of water.

The Definition of the Pressure Tensor in the Statistical Mechanics of Nonuniform Classical Fluids

Abstract: By means of a generalization of the similarity transformation introduced by Bogoliubov and Green to calculate pressure, we derive a unique expression of the pressure tensor for a system of interacting point particles in equilibrium according to the canonical ensemble. Our result confirms the expression originally reported by Irving and Kirkwood.

Decomposition of atmospheric water content into cluster contributions based on theoretical association equilibrium constants

Abstract: Water vapor is treated as an equilibrium mixture of water clusters (H2O)i using quantum-chemical evaluation of the equilibrium constants of water associations. The model is adapted to the conditions of atmospheric humidity, and a decomposition algorithm is suggested using the temperature and mass concentration of water as input information and used for a demonstration of evaluation of the water oligomer populations in the Earth's atmosphere. An upper limit of the populations is set up based on the water content in saturated aqueous vapor. It is proved that the cluster population in the saturated water vapor, as well as in the Earth's atmosphere for a typical temperature/humidity profile, increases with increasing temperatures.