Thermophysical Properties of Diorites along with the Prediction of Thermal Conductivity from Porosity and Density Data

The main focus of this paper involves the use of models to predict the thermophysical properties of diorites. For the prediction of thermal conductivity, an existing mixing law and empirical models have been used. Due to the porosity dependence in all the existing models, ASTM (American Society for Testing and Materials) standard methods have been applied to measure the density, porosity, and specific gravity of diorite rocks taken from the Shewa-Shahbaz Garhi volcanic complex near Mardan, Pakistan. The chemical composition of these samples has been analyzed using the X-ray florescence technique. The theoretically calculated values of specific gravity and the density of the specimen based on the chemical composition and porosity are in good agreement with those obtained from experimental measurements at ambient conditions. The thermal conductivity and thermal diffusivity of these rocks have been measured simultaneously using the transient plane source (TPS) technique at room temperature. The effective thermal conductivity calculated from various models is in agreement with the experimental data within 15%. Simple correlations between estimated density and porosity and between the effective thermal conductivity and porosity are also established.     

Measurement and Analysis of Thermophysical Properties of Diorites in the Temperature Range from 253 to 333 K

Thermal conductivity and thermal diffusivity are simultaneously measured for a collection of diorite samples taken from Shewa-Shahbaz Garhi volcanic complex near Mardan, Pakistan by using the transient plane source (TPS) technique. The temperature dependence of the transport properties of these samples is studied in the temperature range from 253 to 333 K. Different relationships for the temperature dependence of the thermal conductivity and thermal diffusivity are tested. The samples are also characterized by their chemical composition, density, porosity, and specific gravity at room temperature and atmospheric pressure. Theoretical calculation of the specific gravity parameter based on the chemical composition is in good agreement with the experimental observation. No correlation was found for the temperature dependence of the thermal transport behavior on porosity, chemical composition, and density.     

高气孔率莫来石制备、性能及其非线性导热模型

以高铝矾土、硅灰为原料, 玉米淀粉为造孔剂制备高气孔率莫来石, 通过XRD、SEM等对产物物相、形貌进行表征, 研究淀粉含量对显气孔率、体积密度和抗折强度的影响, 及不同显气孔率的莫来石随温度变化的导热系数, 建立体积密度、抗折强度与气孔率关系模型及非线性导热模型。结果表明: 体积密度、抗折强度随气孔率增加而减小, 并符合指数函数关系。导热系数随温度的升高而增大, 实测值与非线性导热模型计算值吻合较好, 非线性导热模型能够准确地反映高气孔率莫来石导热系数与温度、气孔率、平均孔径和热辐射等之间的关系。     

Modeling of the Effective Thermal Conductivity of Consolidated Porous Media with Different Saturants: A Test Case of Gabbro Rocks

The thermal conductivity and thermal diffusivity of porous consolidated gabbro rocks have been measured simultaneously by the transient plane source technique at normal temperature and pressure using air and water as saturants. The density and porosity are measured using American Society for Testing and Materials (ASTM) standards under ambient conditions. The mineral composition is obtained using a petrography technique. Data are presented for 12 specimens of gabbro, taken from Warsik near Peshawar, Pakistan. A recently proposed empirical model for the prediction of the thermal conductivity of porous consolidated igneous rocks is established using different fluids in pore spaces, under ambient conditions. An exponential decay formula is also proposed for the prediction of the thermal conductivity at room temperature and normal pressure. The results are compared with different existing empirical models. A simple correlation between density and porosity is also reported.     

A study of the thermal conductivity of alumina/glass dispersed composites

The thermal diffusivity of five groups of alumina/glass composite systems has been measured at room temperature using a laser flash system. These data have been used, in conjunction with specific heat and density measurements, to calculate the effective thermal conductivity of these composites. In each of the five groups a systematic variation in glass concentration was made, and each group represents systematic variations in glass and alumina particle sizes. The thermal conductivities calculated are compared with those predicted by four models. It is apparent from these comparisons that the geometry and orientation of porosity within the sample measured are a key factor in determining which of these models (if any) is appropriate for describing the thermal conductivity of these composites.Paper presented at the Tenth Symposium on Thermophysical Properties, June 20–23, 1988, Gaithersburg, Maryland, U.S.A.     

The Thermal Conductivity, Thermal Diffusivity and Isobaric Heat Capacity of Toluene and Argon

This paper presents absolute measurements for the thermal conductivity and thermal diffusivity of toluene obtained with a transient hot-wire instrument employing coated wires over the density interval of 735 to 870 kgm^–3. A new expression for the influence of the wire coating is presented, and an examination of the importance of a nonuniform wire radius is verified with measurements on argon from 296 to 323 K at pressures to 61 MPa. Four isotherms were measured in toluene between 296 and 423 K at pressures to 35 MPa. The measurements have an uncertainty of less than ±0.5% for thermal conductivity and ±2% for thermal diffusivity. Isobaric heat capacity results, derived from the measured values of thermal conductivity and thermal diffusivity, using a density determined from an equation of state, have an uncertainty of ±3% after taking into account the uncertainty of the applied equation of state. The measurements demonstrate that isobaric specific heat determinations can be obtained successfully with the transient hot wire technique over a wide range of fluid states provided density values are available.     

基于二维Voronoi模型的多孔泡沫金属导热性能模拟研究

多孔金属材料作为新型功能材料具有密度低、强度高、导热性能优良等特性,应用前景广阔,受到越来越多的关注。多孔材料的有效导热系数与随机孔隙结构相关,仅用孔隙率不足以描述真实材料的孔隙结构。采用二维Voronoi模型,定义孔隙随机度S和孔隙率ε作为孔隙结构参数,通过调节核点位置偏移因子α和边宽系数β改变模型的随机度S和孔隙率ε,分析随机度S和孔隙率ε对相对有效导热系数k*的影响。结果表明,随机度和孔隙率同时影响多孔泡沫材料的有效导热系数,当随机度S一定时,随着孔隙率ε增大,材料的有效导热系数k*减小;当孔隙率ε一定时,随着随机度S的增大,有效导热系数k*减小。根据大样本的有限元数值模拟结果,拟合了有效导热系数由孔隙率和随机度组成的函数表达式。     

加热条件对炭泡沫材料孔结构和性能的影响

以AR沥青为原料,利用高压釜在不同恒温条件下制备了炭泡沫,并测定了其孔结构、体积密度、显气孔率、压缩强度、常温热导率以及微晶参数.结果表明:相对于短恒温时间,长恒温时间制得的炭泡沫孔径大(412nm)、显气孔率高(83.82%)、体积密度小(0.34g/cm~3)、压缩强度高(4.92MPa),多孔连通结构更丰富.经过石墨化处理后,石墨泡沫呈现出较高的常温热导率(71.34W/(m·K))和较小的层片间距d_(002)(0.33556nm).石墨泡沫的常温比导热率能达到210(W·(m·K)~(-1)) /(g·cm~(-3)),是铜的5倍,铝的4倍.     

莫来石含量对钙长石/莫来石复相多孔陶瓷组织结构与性能的影响

以CaCO₃、SiO₂、α-Al₂O₃为原料, 采用泡沫注凝法制备了不同莫来石含量的钙长石/莫来石复相多孔陶瓷, 研究了莫来石含量对复相多孔陶瓷的体积密度、气孔率、抗压强度、热导率及微观组织和结构的影响. 结果表明, 莫来石含量对气孔率有很大的影响, 烧结过程中液相出现引起的收缩是气孔率下降的主要原因; 在气孔率相近的情况下, 莫来石含量较高试样的抗压强度和热导率也较高, 致密的孔壁、长柱状的莫来石晶粒使得复相多孔陶瓷的抗压强度提高. 所制备的钙长石/莫来石复相多孔陶瓷的开口气孔率介于60.8%~75.2%, 抗压强度为12.94~36.95 MPa, 热导率为0.30~1.33 W/(m·K).     

The Thermal Conductivity, Thermal Diffusivity, and Specific Heat of Liquid n-Pentane

The thermal conductivity and thermal diffusivity of liquid n-pentane have been measured over the temperature range from 293 to 428 K at pressures from 3.5 to 35 MPa using a transient hot-wire instrument. It was determined that the results were influenced by fluid thermal radiation, and a new expression for this effect is presented. The uncertainty of the experimental results is estimated to be better than ±0.5% for thermal conductivity and ±2% for thermal diffusivity. The results, corrected for fluid thermal radiation, are correlated as functions of temperature and density with a maximum uncertainty of ±2% for thermal conductivity and ±4% for thermal diffusivity. Derived values of the isobaric specific heat are also given.     

Establishment of an empirical correlation for estimating the thermal conductivity of igneous rocks

A correlation to predict the thermal conductivity of andesitic igneous rocks is developed from measured data on drill cores from wells from the Los Azufres geothermal field, Mexico. The correlation was developed from density, porosity, and thermal conductivity. Seventeen determinations were made on drill cores extracted at varying depths from 12 wells. Thermal conductivity varied from 1.05 to 2.34 W · m^–1 · K^–1, while bulk density varied from 2050 to 2740 kg · m^–3 and grain density varied from 2610 to 2940 kg · m^–3. Total porosity varied from 1.9 to 24.7%. Two polynomial regressions, one linear and one quadratic, were tested on the thermal conductivity-times-bulk density product, with total porosity as the independent variable. The correlation coefficients and residual mean square deviations were 0.83 and 0.00491 for the linear fit and 0.87 and 0.00425 for the quadratic model, respectively. For porosities up to about 18%, both models showed very close predictions, but for larger values, the quadratic model appeared to be better and it is recommended for the porosity range from 0 to 25%. Furthermore, density and porosity may be determined from drill cuttings, which are more readily available than cores.Paper presented at the Tenth Symposium on Thermophysical Properties, June 20–23, 1988, Gaithersburg, Maryland, U.S.A.     

Thermal Conductivity of Saturated Liquid Toluene by Use of Anodized Tantalum Hot Wires at High Temperatures

Absolute measurements of the thermal conductivity of a distilled and dried sample of toluene near saturation are reported. The transient hot-wire technique with an anodized tantalum hot wire was used. The thermal conductivities were measured at temperatures from 300 K to 550 K at different applied power levels to assess the uncertainty with which it is possible to measure liquid thermal conductivity over wide temperature ranges with an anodized tantalum wire. The wire resistance versus temperature was monitored throughout the measurements to study the stability of the wire calibration. The relative expanded uncertainty of the resulting data at the level of 2 standard deviations (coverage factor k = 2) is 0.5 % up to 480 K and 1.5 % between 480 K and 550 K, and is limited by drift in the wire calibration at temperatures above 450 K. Significant thermal-radiation effects are observed at the highest temperatures. The radiation-corrected results agree well with data from transient hot-wire measurements with bare platinum hot wires as well as with data derived from thermal diffusivities obtained using light-scattering techniques.     

Thermophysical properties of MPG-6 graphite

The thermal diffusivity and heat capacity of four MPG-6 graphite samples (density from 1664 up to 1825 kg/m³) are measured within the temperature range from 293 K up to 1650 K by the following methods: the laser flash, the differential scanning calorimetry, and the adiabatic calorimeter of linear heating. The uncertainties of the data on the thermal diffusivity, heat capacity, and density were (2–4)%, (3–5)%, and 0.5%, respectively. On the basis of the measurement results, the temperature dependence of the MPG-6 thermal conductivity is calculated and a generalizing dependence is obtained which allows one to estimate the thermal conductivity of graphite of various porosity for a wide temperature range using only the data on the macroscopic density of the samples. Reference data tables have been developed for the thermal conductivity of MPG-6 graphite of various densities.     

The Thermal Conductivity, Thermal Diffusivity, and Heat Capacity of Gaseous Argon

This paper presents new absolute measurements for the thermal conductivity and thermal diffusivity of gaseous argon obtained with a transient hot-wire instrument. Six isotherms were measured in the supercritical dense gas at temperatures between 296 and 423 K and pressures up to 61 MPa. A new analysis for the influence of temperature-dependent properties and residual bridge unbalance is used to obtain the thermal conductivity with an uncertainty of less than 1% and the thermal diffusivity with an uncertainty of less than 4%. Isobaric heat capacity results were derived from measured values of thermal conductivity and thermal diffusivity using a density calculated from an equation of state. The heat capacities presented here have a nominal uncertainty of 4% and demonstrate that this property can be obtained successfully with the transient hot wire technique over a wide range of fluid states. The technique will be useful when applied to fluids which lack specific heat data.     

Thermal Conductivity of a Simulated Fuel with Dissolved Fission Products

The thermal diffusivity of a simulated fuel with fission products forming a solid solution was measured using the laser-flash method in the temperature range from room temperature to 1673 K. The density and the grain size of the simulated fuel with the solid solutions used in the measurement were 10.49 g · cm⁻³ (96.9% of theoretical density) at room temperature and 9.5 μm, respectively. The diameter and thickness of the specimens were 10 and 1 mm, respectively. The thermal diffusivity decreased from 2.108 m² · s⁻¹ at room temperature to 0.626 m² · s⁻¹ at 1673 K. The thermal conductivity was calculated by combining the thermal diffusivity with the specific heat and density. The thermal conductivity of the simulated fuel with the dissolved fission products decreased from 4.973 W · m⁻¹ · K⁻¹ at 300 K to 2.02 W · m⁻¹ · K⁻¹ at 1673 K. The thermal conductivity of the simulated fuel was lower than that of UO₂ by 34.36% at 300 K and by 15.05% at 1673 K. The difference in the thermal conductivity between the simulated fuel and UO₂ was large at room temperature, and decreased with an increase in temperature. Paper presented at the Seventeenth European Conference on Thermophysical Properties, September 5–8, 2005, Bratislava, Slovak Republic.     

Measurement of the Intrinsic Thermal Conductivity of a Multiwalled Carbon Nanotube and Its Contact Thermal Resistance with the Substrate

The intrinsic thermal conductivity of an individual carbon nanotube and its contact thermal resistance with the heat source/sink can be extracted simultaneously through multiple measurements with different lengths of the tube between the heat source and the heat sink. Experimental results on a 66‐nm‐diameter multiwalled carbon nanotube show that above 100 K, contact thermal resistance can contribute up to 50% of the total measured thermal resistance; therefore, the intrinsic thermal conductivity of the nanotube can be significantly higher than the effective thermal conductivity derived from a single measurement without eliminating the contact thermal resistance. At 300 K, the contact thermal resistance between the tube and the substrate for a unit area is 2.2 × 10^?8 m² K W^?1, which is on the lower end among several published data. Results also indicate that for nanotubes of relatively high thermal conductance, electron‐beam‐induced gold deposition at the tube–substrate contacts may not reduce the contact thermal resistance to a negligible level. These results provide insights into the long‐lasting issue of the contact thermal resistance in nanotube/nanowire thermal conductity measurements and have important implications for further understanding thermal transport through carbon nanotubes and using carbon nanotube arrays as thermal interface materials.     

Thermal conductivity of Cu-4.5 Ti alloy

The thermal conductivity (TC) of peak aged Cu-4.5 wt% Ti alloy was measured at different temperatures and studied its variation with temperature. It was found that TC increased with increasing temperature. Phonon and electronic components of thermal conductivity were computed from the results. The alloy exhibits an electronic thermal conductivity of 46.45 W/m.K at room temperature. The phonon thermal conductivity decreased with increasing temperature from 17.6 at 0 K to 1.75 W/m.K at 298 K, which agrees with literature that the phonon component of thermal conductivity is insignificant at room temperature.     

The thermal conductivity of liquid 1,1,1,2-tetrafluoroethane (HFC 134a)

The thermal conductivity of HFC 134a was measured in the liquid phase with the polarized transient hot-wire technique. The experiments were performed at temperatures from 213 to 293 K at pressures up to 20 MPa. The data were analyzed to obtain correlations in terms of density and pressure. This study is part of an international project coordinated by the Subcommittee on Transport Properties of Commission 1.2 of IUPAC, conducted to investigate the large discrepancies between the results reported by various authors for the transport properties of HFC 134a, using samples of different origin. Two samples of HFC 134a from different sources have been used. The thermal conductivity of the first sample was measured along the saturation line as a function of temperature and the data were presented earlier. The thermal conductivity of the second one, the round-robin sample was measured as a function of pressure and temperature. These data were extrapolated to the saturation line and compared with the data obtained, previously in order to demonstrate the importance of the sample origin and their real purity. The accuracy of the measurements is estimated to be 0.5%. Finally, the results are compared with the existing literature data.     

Effective Thermal Conductivity of Moist Porous Sintered Nickel Material

The effective thermal conductivity of capillary structures is an important parameter in the thermal performance analysis of loop heat pipes (LHP). In this paper, the effective thermal conductivity of porous sintered nickel material filled with water, ethanediol, and glycerin were measured by means of the hot disk thermal constant analyzer. The measured data were compared with similar measured data and calculated values from models in the literature. The results indicate that the thermal conductivity of the porous material depends on the thermal conductivity of the fluid, the filled ratio, and the porosity of the material.Paper presented at the Seventh Asian Thermophysical Properties Conference, August 23–28, 2004, Hefei and Huangshan, Anhui, P. R. China     

The thermal conductivity and heat capacity of gaseous argon

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.