Thermal conductivity and heat capacity of solid nabr under pressure

Using the transient hot-wire method, measurements were made for solid NaBr of both the thermal conductivity and the heat capacity per unit volume. The measurements were performed in the temperature range 100 to 400 K and at pressures up to 2 GPa. An adiabatic compression technique allowed the determination of the thermal expansivity as a function of pressure at room temperature. The heat capacity did not vary with pressure. Analysis of the thermal conductivity data showed that it can be described adequately by the Leibfried-Schlömann formula. For temperatures up to 400 K only acoustic modes needed to be taken into account. A small contribution of optic modes to the heat transport might be apparent at the highest temperatures.     

Thermal conductivity of liquid halogenated ethanes under high pressures

New experimental data on the thermal conductivity of liquid halogenated ethanes, R112 (CCl₂F-CCl₂F), R113 (CCl₂F-CClF₂), R114 (CClF₂-CClF₂), R114B2 (CBrF₂-CBrF₂), and R123 (CHCl₂-CF₃), are presented in the temperature range from 283 to 348 K at pressures up to 200 MPa or the freezing pressures. The measurements were carried out by a transient hot-wire apparatus within an uncertainty of ±1.0%. The thermal conductivity data obtained have been analyzed by means of the corresponding-states principle and other empirical methods. It is found that the corresponding-states correlation =f(T_r, P_r) holds well for R112, R113, and R114. The thermal conductivity can also be correlated satisfactorily with temperature, pressure, and molar volume by a similar expression to the Tait equation and the dense hard-sphere model presented by Dymond.     

Thermal conductivity and heat capacity per unit volume of poly(methyl methacrylate) under high pressure

The thermal conductivity and heat capacity per unit volume of poly(methyl methacrylate) (25 and 350 kg · mol^– in molecular weight) have been measured in the temperature range 155–358 K at pressures up to 2 GPa using the transient hot-wire method. The bulk modulus has been measured up to 1.0 GPa at 294 K and yielded a constant valueg = 3.4 ± 0.3 for the Bridgman parameter. No dependence on molecular weight could be detected in the properties we measured.     

Thermal conductivity of amorphous Teflon (AF 1600) at high pressure

The thermal conductivity, λ of amorphous Teflon AF 1600 [poly(1,3-dioxole-4,5-difluoro-2,2-bis(trifluoromethyl)-co-tetrafluoroethylene)] has been measured at pressures up to 2 GPa in the temperature range 93–392 K. At 295 K and atmospheric pressure, we obtained λ=0.116, W·m⁻¹·K⁻¹. The bulk modulus was measured up to 1.0 GPa in the temperature range 150–296 K and the combined data yielded the following values ofg=(∂ln λ ∂lnp) _r :2.8±0.2 at 296 K, 3.0±0.2 at 258 K, 3.0±0.2 at 236 K. 3.4±0.2 at 200 K. and 3.4±0.2 at 150 K.     

Thermal conductivity, heat capacity, and compressibility of atactic poly(propylene) under high pressure

The thermal conductivity λ and the heat capacity per unit volume of atactic poly(propylene) have been measured in the temperature range 90–420 K at pressures up to 1.5 GPa using the transient hot-wire method. The bulk modulus has been measured in the range 200–295 K and up to 0.7 GPa. These data were used to calculate the volume dependence of λ,g=−[∂λ/λ)/(∂V/V)] _T , which yielded the following values for the glassy state (T<256 K at atmospheric pressure): 3.80±0.19 at 200 K, 3.74±0.19 at 225 K, 3.90±0.20 at 250 K, 3.77±0.19 at 271 K, and 3.73±0.19 at 297 K. The resultant value forg of the liquid state was 3.61±0.15 at 297 K. Values forg which are calculated at 295 K, using theoretical models of λ(T), agree to within 12% with the experimental value for the glassy state.     

Thermal conductivity and heat capacity of solid silver bromide (AgBr) under pressure

The thermal conductivity, , and the heat capacity per unit volume, c _p , have been measured for solid silver bromide (AgBr) using the transient hot-wire method. Measurements were made at temperatures in the range 100–400 K and at pressures up to 2 GPa. c _p was found to be independent of temperature and pressure over these ranges. of AgBr was found to be similar to that of AgCl, which was measured previously. For AgBr, only acoustic phonons needed to be taken into account up to 340 K, but optic phonons probably carried some heat at higher temperatures. The Leibfried-Schlömann (LS) formula could describe the ratio (AgCl)/(AgBr), but not the ratio (1 GPa)/(0) for either substance. An empirical modification of the LS formula could describe the latter ratios but not the former. Further theoretical developments are required for understanding of (P) for even such relatively simple substances as AgCl and AgBr.     

The thermal conductivity of talc as a function of pressure and temperature

Talc is a commonly used pressure-transmitting and gasket material for high-temperature and -pressure applications. The thermal conductivity of talc at high pressures and temperatures is therefore valuable in the design of high-pressure experiments and apparatus. In this paper measurements of the thermal conductivity of fired and unfired talc are presented. Measurements were made at pressures ranging from 0 to 2.5 GPa and temperatures from 150 to 900 K. The thermal conductivity was measured with the hotwire technique. The thermal conductivity results for both the fired and the unfired talc show a slight increase with increasing pressure. The absolute value of the thermal conductivity of talc is lower in the fired material than in the unfired material. In both cases, the thermal conductivity varied less than 15% over the temperature range studied. X-Ray diffraction studies have shown talc to be highly disordered. The results are shown to be consistent with those expected for a disordered crystal.Paper presented at the Tenth Symposium on Thermophysical Properties, June 20–23, 1988, Gaithersburg, Maryland, U.S.A.     

Thermal conductivity of a dendritic ice layer

Measurements of the thermal conductivities of the frozen layer of aqueous binary solutions have been performed using the transient hot-wire method. Solutions of ethylene glycol and sodium chloride were utilized as the testing fluids, and they were frozen up in the test section in which the platinum wires 40 m in diameter and 170 mm in length were strung. Measurements were carried out under equilibrium at a variety of both the initial concentration of the solution and the temperature of the frozen layer. The expressions of the thermal conductivity of the frozen layer were determined. It was found that the thermal conductivity of the dendritic ice layer was favorably assessed with the Lichteneker's model by introducing the solid fraction under an assumption of the equililbrium within the range of parameters examined.Paper presented at the Tenth Symposium on Thermophysical Properties, June 20–23, 1988, Gaithersburg, Maryland, U.S.A.     

Thermal conductivity of B2O3 glass under pressure

The thermal conductivity, , of vitreous boron trioxide was measured, using a hot-wire procedure, from 170 to 570 K and under pressures of up to 1.7 GPa. The thermal conductivity at room temperature and zero pressure was found to be 0.52 W · m^–1 · K^–1. The values of the logarithmic pressure derivative, g = d(ln )/d(ln ), where is the density, were found to be 1.1 for uncompacted glass and 0.7 for glass compacted to 1.2 GPa. The variation of with temperature at constant density was approximately linear, with a positive slope of 1.38×10^–3W·m^–1·K^–2.     

Thermal conductivity and heat capacity of solid AgCl under pressure

Using the transient hot-wire method, measurements were made for solid AgCl of both the thermal conductivity, , and the heat capacity per unit volume, c _p, where is the mass density. Measurements were made in the temperature range 100 to 400 K, and at pressures up to 2 GPa. c _p(P, T) could be adequately described if the acoustic modes were represented by a Debye model and the optic modes by an Einstein model. Analysis of (T) showed that only the acoustic modes needed to be taken into account up to 300 K, but that the optic modes were increasingly effective in carrying heat at higher temperatures. (P) was adequately described by the Lawson formula, but not by the Leibfried-Schlömann formula, to which it is formally equivalent. Agreement with experiment could be achieved by two different modifications of the Leibfried-Schlömann formula, although neither has a firm theoretical basis.     

Thermal conductivity and Lorenz function of zinc under pressure

The thermal conductivity and the Lorenz function L of polycrystalline zinc have been calculated from measured values of the thermal diffusivity a and the electrical resistivity as functions of pressure P up to 2 GPa at room temperature. The effects of convection in, and freezing of, the pressure transmitting medium are discussed. Both and L increase with increasing P, with pressure coefficients of 8.7×10^–2 and 1.5×10^–2 GPa^–1, respectively. The volume dependence of L is found to be similar to that found for other simple metals. Data are also given for the Seebeck coefficient S as a function of P and for a(T) and (T) between 55 and 300 K.     

Measurements of the thermal conductivity of aqueous LiBr solutions at pressures up to 40 MPa

This paper describes absolute measurements of the thermal conductivity of aqueous LiBr solutions in the concentration range 5 to 15m (molality), the temperature range 30 to 100°C, and the pressure range 0.1 to 40 MPa. The measurements have been performed with the aid of a transient hot-wire apparatus employing a thin tantalum wire coated with an anodic tantalum pentoxide insulation layer. In using the tantalum wire, a modification of the bridge circuit has been made to keep the electric potential of the wire always higher than the ground level in order to protect the insulation layer from breakdown. The experimental data, which have an estimated accuracy of ±0.5%, have been correlated in terms of the polynomials of concentration, temperature, and pressure for practical use. Also, it has been found that the pressure coefficient of the thermal conductivity decreases with increasing concentrations.     

Measurement of the thermal conductivity of molten semiconductors

The thermal conductivity of molten InSb in the temperature range between 800 and 870 K was measured by the transient hot-wire method using a ceramic probe. The probe was fabricated from a tungsten wire printed on an alumina substrate and coated with a thin alumina layer. The thermal conductivity was found to be about 18 W· m^–·K^–at the melting point and increased moderately with increasing temperature. The thermal conductivity of alumina used as the substrate for the probe was also measured in the same temperature range.Paper presented at the Tenth Symposium on Thermophysical Properties, June 20–23, 1988, Gaithersburg, Maryland, U.S.A.On leave from NEC Corporation.     

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

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.     

金属氧化物纳米流体的导热性能研究

采用瞬态热线法测量了4种不同种类、不同体积份额配比的纳米流体的导热系数,分析了纳米颗粒属性、体积分数、悬浮稳定性及温度等因素对纳米流体导热系数的影响.实验结果表明,在流体中加入纳米颗粒将显著提高流体的导热系数.     

Thermal conductivity and heat capacity of synthetic fuel components

As part of a group contribution study on the liquid thermal conductivity of synthetic fuel components, experiments were performed to study the effects of dimethyl and ethyl-group additions to cyclohexane. A transient hot-wire apparatus was used to measure the thermal conductivity of these three fluids between ambient pressure and 10.4 MPa over a temperature range of 300 to 460 K. Thermal conductivities measured with this instrument have been assigned an accuracy of ±2% based upon a standard deviation comparison with a toluene standard established by Nieto de Castro et al. (1986). The thermal conductivities and excess thermal conductivities of the naphthenes investigated have been successfully linearized by plotting the data versus reduced density exponentiated to the power of five. By using data previously reported by Perkins (1983) and Li et al. (1984), this linear reduced density method is demonstrated for methyl, dimethyl, and ethyl additions to cyclohexane, as well as methyl and dimethyl additions to benzene. The naphthenes have been shown to have similar intercepts, with slope changes dependent upon the functional group attached to cyclohexane. The aromatics have a less pronounced slope change with additional functional groups attached to the benzene base. This instrument was also used to determine heat capacities, via the thermal diffusivity, to within ±10%.Paper presented at the Tenth Symposium on Thermophysical Properties, June 20–23, 1988, Gaithersburg, Maryland, U.S.A.     

The thermal conductivity of benzene and toluene

The thermal conductivity of liquid toluene and benzene was measured in the temperature range 298 to 370 K, near the saturation line, using an absolute transient hot-wire technique. The measurements were made in a modified version of an existing instrument, equipped with a new automatic Wheatstone bridge, computer controlled. The bridge measures the time that the resistance of a 7-m-diameter platinum wire takes to reach predetermined values, programmed by the computer. The computer can generate up to 1024 analog voltages, via a 12-bit D/A converter. The accuracy of the measurements with this new arrangement was assessed by measuring the thermal conductivity of a primary standard, toluene, at several temperatures and was found to be of the order of 0.3%. Benzene was chosen because it is under study as a possible secondary standard for liquid thermal conductivity by the Subcommittee on Transport Properties of IUPAC.Paper presented at the Tenth Symposium on Thermophysical Properties, June 20–23, 1988, Gaithersburg, Maryland, U.S.A.     

Thermal conductivity of methane-ethane mixtures at temperatures between 140 and 330 K and at pressures up to 70 MPa

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.Paper presented at the Ninth Symposium on Thermophysical Properties, June 24–27, 1985, Boulder, Colorado, U.S.A.     

Thermal conductivity of air in the range 312 to 373 K and 0.1 to 24 MPa

We have used the transient hot-wire technique to make absolute measurements of the thermal conductivity of dry, CO₂-free air in the temperature range from 312 to 373 K and at pressures of up to 24 MPa. The precision of the data is typically ±0.1%, and the overall absolute uncertainty is thought to be less than 0.5%. The data may be expressed, within their uncertainty, by polynomials of second degree in the density. The values at zero-density agree with other reported data to within their combined uncertainties. The excess thermal conductivity as a function of density is found to be independent of the temperature in the experimental range. The excess values at the higher densities are lower than those reported in earlier work.Nomenclature Thermal conductivity, mW · m^–1 · K^–1 - Density, kg · m^–3 - C _p Specific heat capacity at constant pressure, J · kg^–1 · K^–1 - T Absolute temperature, K - q Heat input per unit wire length, W · m^–1 - t Time, s - K(=/C _p) Thermal diffusivity, m² · s^–1 - a Wire radius, m - Euler's constant (=0.5772 ) - p _c Critical pressure, MPa - T _c Critical temperature, K - _c Critical density, kg · m^–3 - R Gas constant (=8.314 J · mol^–1 · K^–1) - V _c Critical volume, m³ · mol^–1 - Z _c(=p _c V _c/RT _c) Critical compressibility factor