Radiative heat exchange method for thermal conductivity measurement applying a perpendicular heat flow to a thin-plate sample: Principle and apparatus

To measure thermal conductivity of materials of low conductivity (0.1 to 1 W·m^–1·K^–1), a method using a specimen of small size (2×25×25 mm) has been developed. This method applies a well-defined, steady, and uniform heat flux perpendicular to the surface of a small plate sample of polymers or ceramics jointly by means of radiative heat exchange as well as by an areal heater on the sample surface and allows a reasonably rapid (5-min) measurement of thermal conductivity. This method of measuring conductivity is an absolute and direct measurement method which does not need any standard reference materials or information about heat capacity. The principle of the method has been demonstrated by constructing a measurement apparatus and measuring thermal conductivity of a few materials. The thermal conductivities of silicone rubber and Pyrex (Corning 7740) glass measured by the present method between 30 and 90°C are compared with recommended values.     

以物体表面温度推算变导热系数的测试原理及技术

提出了一种根据第三类边界条件下物体表面温度的测定值推算随温度线性变化的物体导热系数的测试原理和方法。利用设计的测试系统对几种材料的导热系数进行了测量和计算。结果表明，测试计算方法简单可行。为测定物体变导热系数提供了一个有效的方法。     

Thermal Conductivity of Coated Paper

In this article, a method for measuring the thermal conductivity of paper using a hot disk system is introduced. To the best of our knowledge, few publications are found discussing the thermal conductivity of a coated paper, although it is important to various forms of today’s digital printing where heat is used for imaging, as well as for toner fusing. This motivated an investigation of the thermal conductivity of paper coating. This study demonstrates that the thermal conductivity is affected by the coating mass and the changes in the thermal conductivity affect toner gloss and density. As the coating mass increases, the thermal conductivity increases. Both the toner gloss and density decrease as the thermal conductivity increases. The toner gloss appears to be more sensitive to the changes in the thermal conductivity.     

多层绝热的间隔材料有效低温热导率测试研究

叙述了多层绝热的间隔材料玻璃纤维布、隔热纸的有效低温热导率测试方法,为薄层材料的有效低温热导率测试提供了一种方法,并对测试结果和影响因素,如叠层密度和层密度等进行了讨论分析。     

A procedure to study thermo- and electrophysical properties of materials

We describe a measurement procedure and the construction of an automatic measuring complex to study thermal conductivity by an absolute stationary method and also electrical conductivity and thermal EMF of materials in a temperature range from −60 to +4400 ° C. The use of a specialized microprocessor system to perform stationary measurements and to control parameter measurement processes in combination with highgrade measuring devices and equipment developed for this procedure enables high accuracy of measurements. Test studies performed on reference samples show that the thermal conductivity measurement error does not exceed 4 and 3% for electrical conductivity and thermal EMF, respectively. In the development of devices and equipment for this measuring complex, unconventional engineering, schematic, and programming solutions are implemented. The application of a microprocessor control system together with the software developed allows the measurements to be performed automatically.     

Some problems in measuring thermal conductivity using the coaxial cylinders method. II

The results of an investigation of the thermal conductivity of five liquids using an apparatus based on the absolute coaxial cylinders method are presented. The measurements are made using three different measuring gaps. Procedural problems in measuring thermal conductivity are considered.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 33, No. 2, pp. 275–279, August, 1977.     

Thermal and Electrical Conductivity Measurements on Aluminum Foams

Metal foams are one of the most interesting types of materials although there is limited information concerning their thermal and electrical conductivity. Closed cell different density Alporas foams are investigated, which has one of the most homogeneous cell size distribution recently. Comparative method has been chosen to determine the thermal conductivity of the samples in the function of the temperature at 30, 100, 200, 300, 400, 500 °C. For measuring the electrical conductivity of aluminium foams a special low frequency eddy current measuring apparatus was used. The ratio of thermal and electrical conductivity was calculated and shown an increasing function by the density of the foams.     

An Experimental Technique for Liquid/Solid Thermal Conductivity Measurements at the Melting Point

Based upon the theory that the thermal conductivity can be determined by measuring the speed of the propagation of the solid/liquid phase interface during a phase transition, a system was developed to investigate the thermal conductivity of metals and alloys at the liquid/solid phase transformation point. Furthermore, a mathematical method was applied to represent the melting and solidifying process in the phase transformation chamber, by which the error could be analyzed. In order to test the feasibility of the method and the measuring system, a series of verification experiments on lead have been performed to estimate the precision and the applicability of the measuring system. From comparisons with recommended data from the literature, the uncertainty of the experimental results is estimated to be about 5% which means the measuring method is suitable to determine the thermal conductivity of eutectic alloys and metals at the liquid/solid phase transformation point. This work provides a relatively precise method for thermal conductivity measurements on new materials such as lead-free solders.Paper presented at the Seventh Asian Thermophysical Properties Conference, August 23–28, 2004, Hefei and Huangshan, Anhui, P. R. China     

Application of the Three-Omega Method to Measurement of Thermal Conductivity and Thermal Diffusivity of Hydrogen Gas

Preliminary investigations have been conducted to discuss the possibility of measuring the thermal conductivity of hydrogen gas by the three-omega method. A one-dimensional analytical solution for the 3ω component is derived which includes the effect of the wire heat capacity. It is shown that it is very important to take into account the wire heat capacity in the calculation to measure the thermal conductivity of gas by the three-omega method. In contrast, the wire heat capacity is less important for the thermal conductivity of the liquid or solid phase. The importance of the wire heat capacity is found to increase with increasing frequency and decrease if the sample thermal conductivity is high. In order to measure the thermal conductivity of hydrogen gas at atmospheric pressure, a wire of diameter less than 1μm is necessary if the properties of the wire are to be neglected.     

Thermal Conductivity and Viscosity Measurements of Water-Based TiO<Subscript>2</Subscript> Nanofluids

In this study, the thermal conductivity and viscosity of TiO₂ nanoparticles in deionized water were investigated up to a volume fraction of 3% of particles. The nanofluid was prepared by dispersing TiO₂ nanoparticles in deionized water by using ultrasonic equipment. The mean diameter of TiO₂ nanoparticles was 21 nm. While the thermal conductivity of nanofluids has been measured in general using conventional techniques such as the transient hot-wire method, this work presents the application of the 3ω method for measuring the thermal conductivity. The 3ω method was validated by measuring the thermal conductivity of pure fluids (water, methanol, ethanol, and ethylene glycol), yielding accurate values within 2%. Following this validation, the effective thermal conductivity of TiO₂ nanoparticles in deionized water was measured at temperatures of 13 °C, 23 °C, 40 °C, and 55 °C. The experimental results showed that the thermal conductivity increases with an increase of particle volume fraction, and the enhancement was observed to be 7.4% over the base fluid for a nanofluid with 3% volume fraction of TiO₂ nanoparticles at 13 °C. The increase in viscosity with the increase of particle volume fraction was much more than predicted by the Einstein model. From this research, it seems that the increase in the nanofluid viscosity is larger than the enhancement in the thermal conductivity.     

The use of an explicit method of identifying objects to solve problems of nonstationary heat conduction

The theoretical principles of an explicit method of identifying multidimensional objects with nonstationary thermal conductivity are described. The solution of problems of measuring nonstationary heat flux and thermal conductivity in the range λ = 0.03–800 W/(m·K), the thermal conductivity of one of the materials of a double-layer system, the temperature dependence of the thermal conductivity, and the combined “thermal conductivity and volume heat capacity” are presented. The results of investigations on thermal models are given. __________ Translated from Izmeritel’naya Tekhnika, No. 6, pp. 32–38, June, 2008.     

纳米低温保护剂导热系数研究

用瞬态热线法测量了SiO2纳米粉体加入到浓度为10%、20%、30%、40%、50%的丙三醇溶液中制备成的纳米低温保护剂在260K~290K下的导热系数,研究纳米低温保护剂导热系数与纳米颗粒含量、保护剂浓度以及温度的关系。结果表明：随着纳米颗粒的添加量增多（0.5g/L-1g/L),甘油溶液导热系数增大;甘油浓度从10%升高到50%时,纳米低温保护剂导热系数增加率也随之提高,从0.4%提高到6.8%;纳米低温保护剂导热系数随温度降低而减小,当温度低于260K后,纳米颗粒对保护剂导热系数几乎无影响。建议应用在解冻和复温过程中。     

Thermal Conductivity Measurement of Anisotropic Biological Tissue In Vitro

The accurate determination of the thermal conductivity of biological tissues has implications on the success of cryosurgical/hyperthermia treatments. In light of the evident anisotropy in some biological tissues, a new modified stepwise transient method was proposed to simultaneously measure the transverse and longitudinal thermal conductivities of anisotropic biological tissues. The physical and mathematical models were established, and the analytical solution was derived. Sensitivity analysis and experimental simulation were performed to determine the feasibility and measurement accuracy of simultaneously measuring the transverse and longitudinal thermal conductivities. The experimental system was set up, and its measurement accuracy was verified by measuring the thermal conductivity of a reference standard material. The thermal conductivities of the pork tenderloin and bovine muscles were measured using the traditional 1D and proposed methods, respectively, at different temperatures. Results indicate that the thermal conductivities of the bovine muscle are lower than those of the pork tenderloin muscle, whereas the bovine muscle was determined to exhibit stronger anisotropy than the pork tenderloin muscle. Moreover, the longitudinal thermal conductivity is larger than the transverse thermal conductivity for the two tissues and all thermal conductivities increase with the increase in temperature. Compared with the traditional 1D method, results obtained by the proposed method are slightly higher although the relative deviation is below 5 %.     

热探针法测定含湿土壤的导热系数

根据线热源瞬态导热模型,设计制作了用于测定含湿土壤导热系数的热探针,研究了加热功率、加热时间、探针壁厚对导热系数测定的影响。对不同含水量的土壤导热系数进行测定,得出纯土、河沙含水量～导热系数拟合关系式。结果表明,热探针法测定含湿土壤的导热系数具有便捷、准确的特点。     

第三类边界条件下利用物体表面温度推算物体导热系数的实验技术

提出了一种根据第三类边界条件下物体瞬态温度场的变化规律，利用物体表面温度的实测值推算物体导热系数的快速测定方法。设计了一种可以在较高表面换热强度条件下进行测试的装置，导热系数的测定范围较宽。实验结果表明，测试方法简单，测试时间短。比较实用可靠。     

航天器用十一种热控材料热物理性质及其与显微组织和工艺因素关系的研究

应用自行研制的激光脉冲法热导仪、小平板稳态法热导仪、铜卡计和冰卡计法比热仪, 对航天器用的十一种热控材料的导热系数、导温系数和比热及其与材料显微组织和工艺因素的关系进行了实验研究. 结果表明, 在室温至1800℃温区内, 绝热材料和防热材料的导热系数均随温度升高而增大, 多孔绝热材料的有效导热系数是由多种导热因子相互作用的结果, 并存在对应于最小导热系数的最佳密度. 所得数据为热控材料的优选提供了科学判据, 亦为航天器的热控系统热设计提供了参数.     

A method and instrument for measuring the thermal properties of samples of a regenerative product in a matrix when they are heated by a constant heat flux

A mathematical model of a method of measuring the thermal properties of new regenerative products is developed. The construction of a measuring instrument is proposed. Experimental data on the thermal conductivity and volume heat capacity of regenerative products in a matrix are obtained. Translated from Izmeritel’naya Tekhnika, No. 5, pp. 49–53, May, 2009.     

Determining Thermal Conductivity and Thermal Diffusivity of Low-Density Gases Using the Transient Short-Hot-Wire Method

The transient short-hot-wire method for measuring thermal conductivity and thermal diffusivity makes use of only one thermal-conductivity cell, and end effects are taken into account by numerical simulation. A search algorithm based on the Gauss–Newton nonlinear least-squares method is proposed to make the method applicable to high-diffusivity (i.e., low-density) gases. The procedure is tested using computer-generated data for hydrogen at atmospheric pressure and published experimental data for low-density argon gas. Convergence is excellent even for cases where the temperature rise versus the logarithm of time is far from linear. The determined values for thermal conductivity from experimental data are in good agreement with published values for argon, while the thermal diffusivity is about 10 % lower than the reference data. For the computer-generated data, the search algorithm can return both thermal conductivity and thermal diffusivity to within 0.02 % of the exact values. A one-dimensional version of the method may be used for analysis of low-density gas data produced by conventional transient hot-wire instruments.     

Bi2Sr2CaCu2O8＋x单晶的热导率测量

介绍了有关高温超导材料的热导率性质、测试方法和测试结果。结合我们的测试经验，讨论了稳态热流法测量高温超导体热导率应注意的问题。给出了Ｂｉ２Ｓｒ２ＣａＣｕ２Ｏ８＋ｘ单晶沿ａｂ面热导率的测试结果。