Thermal conductivity of aqueous solutions of NaCl and KCI at high pressures

This paper presents new experimental measurements of the thermal conductivity of aqueous solutions of NaCl and KCl at high pressures. The measurements were made with a parallel-plate apparatus. The temperatures covered the range from 293 to 473 K at pressures up to 100 MPa and concentrations from 0.025 to 0.25 mass fraction of NaCl and KCl. The measurements included 6 isobars at pressures from 0.1 to 100 MPa at intervals of 20 MPa, 10 isotherms at temperatures from 293 to 473 K at intervals of 20 K, and 6 isopleths at concentrations from 0.025 to 0.25 mass fraction of NaCl and KCl at intervals of 0.05. The precision of the measurements was ±1.6%. The thermal conductivity obtained for NaCl + H₂O and KCl + H₂O was compared with data of other authors, with satisfactory agreement. The viability of the technique was confirmed and the essential features of a high-precision instrument were established.     

Comparison of the thermal conductivities of water and heavy water

New measurements of the thermal conductivity of H₂O and D₂O have been performed from critical temperature up to 510°C and from atmospheric pressure up to 100 MPA. As these measurements have been made with the same cell, a precise analysis of the isotopic effect as a function of temperature and density is possible. Our analysis is presented in terms of corresponding states. It is shown that the critical thermal conductivity excesses for H₂O and D₂O reduced by their respective background thermal conductivity terms are represented by single reduced isotherms.Paper presented at the Ninth Symposium on Thermophysical Properties, June 24–27, 1985, Boulder, Colorado, U.S.A.     

Experimental measurement of thermophysical properties of H2O/KCOOH (potassium formate) desiccant

This paper presents the measurement of the thermal conductivity and the dynamic viscosity of H₂O/KCOOH (potassium formate) desiccant with a salt concentration from 60 to 80% in the temperature range 1–80 °C. The thermal conductivity measurement gives evidence of a great sensitivity to salt concentration and lower sensitivity to temperature: H₂O/KCOOH desiccant shows a thermal conductivity from 23 to 33% lower than water at the same temperature. H₂O/KCOOH desiccant exhibits a Newtonian behaviour in all the investigated ranges of temperature and concentration. The relative viscosity shows a great sensitivity to salt concentration and weak or no sensitivity to temperature up to a solution concentration of salt around 70%. For higher solution concentration of salt (75 and 80%) the relative viscosity shows a great sensitivity also to temperature. H₂O/KCOOH desiccant presents a dynamic viscosity from 4 to 30 times higher than water at the same temperature.     

The melting curve of tetrahydrofuran hydrate in D2O

Melting points for the tetrahydrofuran/D₂O hydrate in equilibrium with the airsaturated liquid at atmospheric pressure are reported. The melting points were measured by monitoring the absorbance of the solution. Overall, the meltingpoint phase boundary curve is about 2.5 K greater than the corresponding curve for the H₂O hydrate, with a congruent melting temperature of 281±0.5 K at a D₂O mole fraction of 0.936. The phase boundary is predicted to within 5% if the assumption is made that the THF occupancy in the D₂O and H₂O hydrates is the same. We measure an occupancy of 99.9%. The chemical potential of the empty lattice in D₂O is estimated to be 5% greater than in H₂O.     

Thermal conductivity of gaseous fluorocarbon refrigerants R 12, R 13, R 22, and R 23, under pressure

The thermal conductivity of four gaseous fluorocarbon refrigerants has been measured by a vertical coaxial cylinder apparatus on a relative basis. The fluorocarbon refrigerants used and the ranges of temperature and pressure covered are as follows: R 12 (Dichlorodifluoromethane CCl₂F₂): 298.15–393.15 K, 0.1–4.28 MPa R 13 (Chlorotrifluoromethane CClF₃): 283.15–373.15 K, 0.1–6.96 MPa R 22 (Chlorodifluoromethane CHClF₂): 298.15–393.15 K, 0.1–5.76 MPa R 23 (Trifluoromethane CHF₃): 283.15–373.15 K, 0.1–6.96 MPaThe apparatus was calibrated using Ar, N₂, and CO₂ as the standard gases. The uncertainty of the experimental data is estimated to be within 2%, except in the critical region. The behavior of the thermal conductivity for these fluorocarbons is quite similar; thermal conductivity increases with increasing pressure. The temperature coefficient of thermal conductivity at constant pressure, (/T) _p , is positive at low pressures and becomes negative at high pressures. Therefore, the thermal conductivity isotherms of each refrigerant intersect each other in a specific range of pressure. A steep enhancement of thermal conductivity is observed near the critical point. The experimental results are statistically analyzed and the thermal conductivities are expressed as functions of temperature and pressure and of temperature and density.     

Thermal conductivity of R32 and its mixture with R134a

The liquid thermal conductivity of R32 (CH₂F₂) and R134a (CF₃CH₂F) was measured in the range from 223 to 323 K and from 2 to 20 MPa by the transient hot-wire method. The thermal conductivity of the R32+R134a mixture was also measured in the same range by varying the mass fraction of R32. The measured data are analyzed to obtain a correlation in terms of temperature, pressure and composition of the mixture. The uncertainty of our measurements is estimated to be within ±2%.Paper presented at the Twelfth Symposium on Thermophysical Properties, June 19–24, 1994, Boulder, Colorado, U.S.A.     

Liquid Thermal Conductivity of Binary Mixtures of Pentafluoroethane (R125) and 1,1,1,2-Tetrafluoroethane (R134a)

Thermal conductivities of zeotropic mixtures of R125 (CF₃CHF₂) and R134a (CF₃CH₂F) in the liquid phase are reported. Thermal conductivities have been measured by a transient hot-wire method with one bare platinum wire. Measurements have been carried out in the temperature range of 233 to 323 K and in the pressure range of 2 to 20 MPa. The dependence of thermal conductivity on temperature, pressure, and composition of the binary mixture is presented. Measured thermal conductivity data are correlated as a function of temperature, pressure, and overall composition of the mixture. The uncertainty of our measurements was estimated to be better than 2%.     

Thermal Conductivity of Methane-Hydrate

The thermal conductivity of the methane hydrate CH₄ (5.75H₂O) was measured in the interval 2–140 K using the steady-state technique. The thermal conductivity corresponding to a homogeneous substance was calculated from the measured effective thermal conductivity obtained in the experiment. The temperature dependence of the thermal conductivity is typical for the thermal conductivity of amorphous solids. It is shown that after separation of the hydrate into ice and methane, at 240 K, the thermal conductivity of the ice exhibits a dependence typical of heavily deformed fine-grain polycrystal. The reason for the glass-like behavior in the thermal conductivity of clathrate compounds has been discussed. The experimental results can be interpreted within the phenomenological soft-potential model with two fitting parameters.PACS numbers: 66.70 +f, 63.20 −e, 63.20 Pw, 63.50 +x.     

Thermal Conductivity of Aqueous Solutions of KCl–NaCl–CaCl2 System at High Temperatures and Pressures

The experimental data are obtained on the thermal conductivity of mixed aqueous solutions of KCL, NaCl, and CaCl₂ salts in a temperature range of 20–300°C, at a pressure of 5–50 MPa, and a concentration of 3–20 wt %. The experiments are carried out on a setup realizing the relative method of coaxial cylinders. The error of the experimental data is ±(1.3–1.8)%. An empirical formula is presented which correlates the thermal conductivity of the solution with the densities of the solvent and solution, as well as with the thermal conductivity of water. This formula enables one to calculate the thermal conductivity of aqueous solutions of salts at high temperatures. The error of calculation by this formula corresponds to the experimental error. As an example, the values of the thermal conductivity of the H₂O–KCl–CaCl₂ system are calculated in a temperature range of 20–80°C. The maximal discrepancy between the experimental and theoretical data is 1.4%.     

Thermodynamic properties for the quaternary system H2O + CH3OH + LiBr + ZnCl2

The thermodynamic properties (solubility, vapour pressure, density, viscosity, heat capacity and heat of mixing) of the H₂O + CH₃OH + LiBr + ZnCl₂ (9:1 H₂O:CH₃OH and 1:1 LiBr:ZnCl₂ by mass) system using H₂O + CH₃OH as the working media and LiBr + ZnCl₂ as the absorbents were measured. The solubility data were obtained in the temperature range from 270.35 to 389.55 K. The measurements of vapour pressure, density, viscosity and heat capacity were carried out at various temperatures and absorbent concentrations. The differential heat of dilution and differential heat of solution at 298.15 K were measured for solutionw with absorbent concentrations from 0 to 75.2 wt%. The integral heat of mixing data at 298.15 K were obtained from both sets of experimental data. The integral heats of mixing for this quaternary system showed exothermic behaviour. The vapour pressure data were correlated with an Antoine-type equation. An empirical formula for the heat capacity was obtained from experimental data. The experimental data for the basic thermodynamic properties of this quaternary system were compared with those of the basic H₂O + LiBr system.     

Thermal conductivity andPVT measurements of pentafluoroethane (refrigerant HFC-125)

By means of the transient and steady-state coaxial cylinder methods, the thermal conductivity of pentafluoroethane was investigated at temperatures from 187 to 419 K and pressures from atmospheric to 6.0 MPa. The estimated uncertainty of the measured results is ±(2–3)%. The operation of the experimental apparatus was validated by measuring the thermal conductivity of R22 and R12. Determinations of the vapor pressure andPVT properties were carried out by a constant-volume apparatus for the temperature range 263 to 443 K, pressures up to 6 MPa, and densities from 36 to 516 kg m^–3. The uncertainties in temperature, pressure, and density are less than ±10 mK, ±0.08%, and ±0.1%, respectively.Paper presented at the Twelfth Symposium on Thermophysical Properties, June 19–24, 1994, Boulder, Colorado, U.S.A.     

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%.     

Experimental investigation of the thermal properties of a binaryn-hexane-water mixture at high temperatures and pressures

The results are presented of an experimental investigation of the thermal properties of a binaryn-C₆H₁₄ + H₂O mixture (system) in the ranges of temperature from 372.75 to 690.55 K, density from 66.87 to 834.30 kg/m, and pressure from 0.4 to 65.7 MPa. Measurements are performed for seven values of water concentrationx (in molar fractions), namely, 0.166, 0.257,0.347,0.615,0.827,0.935, and 0.964. The investigations cover the region of liquid-vapor phase equilibrium and extend further into the homogeneous region. In order to describe theP-V-T-x properties of a binary n-hexane-water mixture, the Soave-Redlich-Kwong formula is used (the average error is 3%, and the maximum error is 8%). Based on the scaling equations, the critical indices and amplitudes for the curves of liquid-vapor coexistence are calculated for three values of water concentration.     

Low temperature conductivity of Gd2(SO4)38H2O and Dy2Ti2O7 as a function of magnetic field

The thermal conductivities of pressed powders of Gd₂(SO₄)₃8H₂O and Dy₂Ti₂O₇ and a single crystal of Gd₂(SO₄)₃8H₂O were measured in the range 3 to 9 K. At approximately 4 K the thermal conductivities were measured as a function of magnetic field from 0 to 1.8 T. The single crystal had better thermal conductivity than the pressed powders and no significant field dependence was detected in any sample.     

Electrical transport in magnesium aluminate

The conductivity of MgAl₂O₄ has been measured at 1273, 1473 and 1673 K as a function of the partial pressure of oxygen ranging from 10⁵ to 10⁻¹⁴ Pa. The MgAl₂O₄ pellet, sandwiched between two platinum electrodes, was equilibrated with a flowing stream of either Ar + O₂, CO + CO₂ or Ar + H₂ + H₂O mixture of known composition. The gas mixture established a known oxygen partial pressure. All measurements were made at a frequency of 1 kHz. These measurements indicate pressure independent ionic conductivity in the range 1 to 10⁻¹⁴ Pa at 1273 K, 10⁻¹ to 10⁻¹² Pa at 1473 K and 10⁻¹ to 10⁻⁴ Pa at 1673 K. The activation energy for ionic conduction is 1·48 eV, close to that for self-diffusion of Mg²⁺ ion in MgAl₂O₄ calculated from the theoretical relation of Glyde. Using the model, the energy for cation vacancy formation and activation energy for migration are estimated.     

Ionic Conductivity of (PbOH)2V12O31 · nH2O

The 333-K complex impedance and temperature-dependent 10-kHz electrical conductivity of the cell Ni|(PbOH)₂V₁₂O₃₁ · nH₂O|Ni were measured. The results demonstrate that heat treatment changes the conductivity of (PbOH)₂V₁₂O₃₁ · nH₂O. After the removal of hydrate water, the activation energy for conduction in the range 203–485 K is 0.27 eV. The polarization resistance of the Ni electrodes is 31% of the total resistance of the cell at 296 K and is nearly zero above 303 K. The potential of the system lead polyvanadate/lead varies linearly with the Pb²⁺ concentration in aqueous Pb(NO₃)₂ solutions.     

Thermo-physical properties of Al2O3-SiO2/PAG composite nanolubricant for refrigeration system

Thermal conductivity and viscosity of the Al₂O₃-SiO₂/PAG composite nanolubricants for 0.02 to 0.1% volume concentrations at a temperature range of 303 to 353 K were investigated. Al₂O₃ and SiO₂ nanoparticles were dispersed in the Polyalkylene Glycol (PAG 46) lubricant using the two-step method of preparation. Thermal conductivity and viscosity were measured using KD2 Pro Thermal Properties Analyzer and LVDV-III Rheometer, respectively. The result shows that the thermal conductivity and viscosity of composite nanolubricants increase with volume concentration and decreases with temperature. Composite nanolubricants behave as Newtonian in the range of the temperatures and volume concentrations studied. The highest thermal conductivity increment is 2.41% at 0.1% concentration and temperature of 303 K. A maximum value of 9.71% in viscosity at 0.1% concentration is observed at temperature of 333 K. A new correlation model to predict the properties of composite nanolubricants has been proposed for applications in refrigeration systems.     

Thermal conductivity of heavy-oxygen water H2O18

The ratio of thermal conductivity coefficients of heavy-oxygen water H₂O¹⁸ with different percentages of enrichment to the thermal conductivity coefficient of ordinary water is measured in the range of 0–40°C. Differences in the thermal conductivities and the temperature coefficients of the thermal conductivity of heavy-hydrogen water D₂O and and heavy-oxygen water H₂O¹⁸ are indicated.     

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.     

The Excess Enthalpy of (Steam+Ethane) in the Supercritical Region up to T=699.4 K and p=25.3 MPa

Flow calorimetric measurements of the excess molar enthalpy H ^E _m of (0.5H₂O+0.5C₂H₆) in the supercritical region carried out at temperatures from 573.7 to 699.4 K and at pressures in the range 5.05 to 25.3 MPa are reported. The measurements are fitted by a two-reference-fluid corresponding-states model which gives a good representation of the excess enthalpies up to the highest pressure.