Thermal Conductivity of Binary Refrigerant Mixtures of HFC-32/125 and HFC-32/134a in the Liquid Phase

The liquid thermal conductivity of mixtures of HFC-32/125 and HFC-32/134a was measured using the transient hot-wire apparatus in the temperature ranges from 213 to 293 K and from 193 to 313 K, respectively, in the pressure range from 2 to 30 MPa and with HFC-32 mass fractions of 0.249, 0.500, and 0.750 for each system. The uncertainty of the thermal conductivity was estimated to be ±0.7%. For practical applications, the thermal conductivity data for the two mixtures were represented by a polynomial in temperature, pressure, and mass fraction of HFC-32 with a standard deviation of 1.0%.     

Thermal Conductivity Measurements of Aqueous SrCl2 and Sr(NO3)2 Solutions in the Temperature Range Between 293 and 473 K at Pressures up to 100 MPa

Accurate high-pressure thermal conductivity measurements have been performed on H₂O+SrCl₂ and H₂O+Sr(NO₃)₂ mixtures at pressures up to 100 MPa over a temperature range between 293 and 473 K using a parallel-plate apparatus. The concentrations studied were 0.025, 0.05, 0.10, 0.15, and 0.20 mass fraction of the salts. The estimated accuracy of the method is about ±1.6%. The pressure, temperature, and concentration dependences of the thermal conductivity have been studied. Measurements were made on six isobars, namely, 0.1, 20, 40, 60, 80, and 100 MPa. The thermal conductivity shows a linear dependence on pressure and concentration for all isotherms. Along each isobar, a given concentration shows the thermal-conductivity maximum at a temperature of about 413 K. The measured values of thermal conductivity at atmospheric pressure are compared with the results of other investigators. Literature data at atmospheric pressure reported by Ridel and by Zaitzev and Aseev agree with our thermal conductivity values within the estimated uncertainty.     

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.     

高体积分数SiCP/ Al 复合材料电子封装盒体的制备

采用注射成型方法制备了SiC_P封装盒体的预成型坯, 用压力浸渗方法将熔融铝浸渗到SiC_P封装盒体的预成型坯中, 制备出含SiC_P体积分数为65 %的SiC_P / Al 复合材料的封装盒体。SEM 观察表明, 经过压力浸渗后SiC_P / Al 复合材料组织均匀且致密化高, 室温热膨胀系数为8. 0 ×10-6 / K, 热导率接近130 W/ (m·K) , 密度为2198 g/ cm3 , 能够很好地满足电子封装的要求。      

Thermal expansion of an E-glass/vinyl ester composite from 4 to 293 K

We have measured the thermal expansion of the three principal orthogonal directions of an E-glass/vinyl ester structural composite from liquid helium temperature, 4.2 K, to room temperature, 293 K. The linear thermal expansion at 4.2 K ranged from −0.23 to −0.71%, referenced to zero expansion at 293 K. We fitted the linear thermal expansion data from 4.2 to 293 K with a cubic polynomial for each of the three principal orthogonal directions.     

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.     

SiC换热器材料热物理性质的研究

本文采用ＴＬＰ－１８型激光热常数仪和岛津ＴＭＡ－３０热分析仪研究了温度对等静压ＳｉＣ换热器材料的导热系数和热膨胀系数的影响，并对影响ＳｉＣ抗热震性能的各因素进行了分析。     

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.     

高压熔渗金刚石/铜复合材料的低温导热特性

为研究高压熔渗金刚石/铜复合材料导热率在低温区的变化规律,采用高压熔渗（HRF）的方法分别制备了不同粒度（100 μm,250 μm,400 μm）的金刚石/铜复合材料,利用扫描量热法分析评价了高压熔渗法制备的不同粒度金刚石/铜复合材料的低温导热特性,采用扫描电子显微镜（SEM）分析其显微组织。研究结果表明：由于高压熔渗制备的金刚石/铜复合材料中的部分金刚石发生聚晶反应,导致金刚石颗粒间晶界传热的热阻远小于界面传热热阻;高压熔渗条件下,金刚石颗粒内部变形破碎导致缺陷增多,且100~150 K低温下以声子为主要热载子的传热对裂纹和间隙等缺陷敏感,导致在较低温区内金刚石/铜复合材料的导热率低于普通压力熔渗（PF）所制备的金刚石/铜复合材料的导热率。     

Measurement of thermal conductivity of cis-1,1,1,4,4,4-hexafluoro-2-butene (R-1336mzz(Z)) by the transient hot-wire method

A Hydro-Fluoro-Olefin refrigerant cis-1,1,1,4,4,4-hexafluoro-2-butene (R-1336mzz(Z)) has low global warming potentials and it is considered as a potential working fluid for high temperature heat pump and Organic Rankine Cycle. Thermophysical properties of this fluid are necessary to be used in practical system. In this work, thermal conductivity of R-1336mzz(Z) is measured using a well-known transient hot wire method. A polarization voltage of 6 V was applied to minimize the effect of polarity. The thermal conductivity of liquid and gaseous R-1336mzz(Z) is measured in the temperature which ranges from 314 K to 435 K and 321 K to 496 K, respectively at a pressure up to 4 MPa and proposed simplified correlations. Total standard uncertainties of thermal conductivity measurements in liquid and gas phase were estimated to be less than ±2.07% and ±2.26% respectively and near the critical temperature, the uncertainty increases to ±3.40%.     

Effective thermal conductivity of Cu/diamond composites containing connected particles

An analytical model for the thermal conductivity of Cu/diamond composites with connected particles is presented by replacement of a cluster of connected particles with an equivalent polycrystal subsequently using a multiple effective medium approach. By applying this model to the measured thermal conductivity of Cu/diamond composites prepared by high pressure high temperature sintering technique reported in the literature, we show that it quite well describes the observed thermal conductivity enhancement induced by the connected particles. We estimate the value of connected particle loading in real composites and show that large particles are easier to form the bonding contact than small particles. The present work also demonstrates that the sensitivity of thermal conductivity contribution from the connected particles strongly depends on the particle size, and their pronounced thermal conductivity enhancement should lie within the certain particle size range.     

Thermophysical Properties of Porous Sandstones: Measurements and Comparative Study of Some Representative Thermal Conductivity Models

The thermal conductivity and thermal diffusivity of porous consolidated sandstones have been measured simultaneously by the transient-plane source (TPS) technique in the temperature range from 280 to 330 K at ambient pressure using air as the saturant. The porosity and density parameters are measured using standard American Society for Testing and Materials (ASTM) methods at 307 ± 1 K. Data are presented for five types of samples ranging in porosity from 8 to 17 vol. %, taken from various positions above the baseline. The thermal conductivity and constituents of the minerals vary with porosity as well as with the position of the sample from the baseline. The thermal conductivity data are discussed in the framework of simple mixing laws and empirical models. Simple correlations between the effective density and porosity, and between the effective thermal conductivity and porosity, are also established     

Modeling of Effective Thermal Conductivity of Dunite Rocks as a Function of Temperature

The thermal conductivity, thermal diffusivity, and heat capacity per unit volume of dunite rocks taken from Chillas near Gilgit, Pakistan, have been measured simultaneously using the transient plane source technique. The temperature dependence of the thermal transport properties was studied in the temperature range from 303 K to 483 K. Different relations for the estimation of the thermal conductivity are applied. A proposed model for the prediction of the thermal conductivity as a function of temperature is also given. It is observed that the values of the effective thermal conductivity predicted by the proposed model are in agreement with the experimental thermal conductivity data within 9%.     

Thermal conductivity of BaWO4 single crystal

Barium tungstate (BaWO₄) single crystal has been grown using Czochralski technique. It belongs to the scheelite structure, forming the space group I4₁/a at room temperature and the primitive cell contains two formular units. The thermal expansion, specific heat and thermal diffusivity were measured, and then the thermal conductivity was calculated. These results show that BaWO₄ possesses large anisotropic thermal expansion and its thermal expansion coefficients are _a = 1.10 × 10⁻⁵/K, _b = 1.08 × 10⁻⁵/K, and _c = 3.51 × 10⁻⁵/K in the temperature range from 303 to 1423 K. However, its thermal conductivity shows small anisotropic in the temperature range from 297 to 563 K and even displays isotropic at about 428 K. The calculated thermal conductivities are 2.59 and 2.73 W m⁻¹ K⁻¹ at room temperature, along [1 0 0] and [0 0 1] directions, respectively.     

Effects of Sintering Process on Microstructure and Properties of Flake Graphite-Diamond/Copper Composites

Flake graphite-diamond/Cu–Cr–Zr composites with good two-dimensional thermophysical properties were prepared by vacuum hot-pressing technology. The influence and working mechanism of the hot-pressing temperature on the relative density and thermal conductivity of the composites were studied to obtain the optimum sintering process. The results showed that with a pressing pressure of 10 ～ 20 MPa, the relative density and thermal conductivity of the composite materials increased as the sintering temperature increased from 950 to 1010°C. When the temperature rose to 1010 ～ 1040°C, a near fully dense composite material was obtained and thermal conductivity reached maxima of 410 and 119 W/m K parallel and perpendicular to the graphite planes, respectively, both of which are close to the theoretical value. However, relative density and thermal conductivity drastically decreased as the temperature continued to increase beyond 1070°C. This is attributed to the combined effect of sintering temperature and wettability between the matrix and the reinforcements.     

Thermal Conductivity of HFC-32, HFC-125, and HFC-134a in the Solid Phase

Measurements of the thermal conductivity of HFC-32, HFC-125, and HFC-134a were carried out for the first time in both solid and liquid phases at the saturation pressure at room temperature and in the temperature ranges from 120 to 263, from 140 to 213, and from 130 to 295 K, respectively. A transient hot-wire instrument using one bare platinum wire was employed for measurements, with an uncertainty of less than ±2%. The experimental results demonstrated that the thermal conductivity of HFC-32, HFC-125, and HFC-134a in the solid phase showed a positive temperature dependence. For HFC-32 and HFC-125, there were big jumps between the solid and the liquid thermal conductivity at the melting point. But for HFC-134a, the solid and liquid thermal conductivity at the melting point is almost-continuous.     

Experimental determination of the thermal conductivity of binary gas mixtures

A test apparatus is described for determining the thermal conductivity of gases and gas mixtures by the hot filament method. Values have been obtained for helium and argon as well as for their mixtures within the 293–394°K temperature range under a pressure of P = 1 atm.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol.22, No. 5, pp. 843–849, May, 1972.     

High temperature electrical and thermal properties of the bulk carbon nanotube prepared by SPS

Bulk multi-walled carbon nanotube was prepared by spark plasma sintering at 1700 °C under a pressure of 50 MPa in vacuum. The density of the bulk sample reaches 72% of the theoretical density of the carbon nanotube, 2 g/cm³. The high temperature thermal conductivity and electrical conductivity of the bulk material were measured in the directions perpendicular and parallel to the pressure direction. Both the thermal conductivity and electrical conductivity show apparent anisotropy. The thermoelectric power has close values in the two different directions and takes positive values in the whole measured temperature range (360–840 K).     

The thermophysical properties of hafnium in the temperature range from 293 to 2000 K

The temperature dependences are given of enthalpy, heat capacity, mean temperature coefficient of linear expansion, density, thermal conductivity, thermal diffusivity, and emissive properties of hafnium in the temperature range from 293 to 2000 K, which are obtained as a result of analysis and simultaneous processing of literature data.     

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.