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.     

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.     

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.     

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.     

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.     

Thermal conductivity of polymer composites based on the length of multi-walled carbon nanotubes

The anisotropic development of thermal conductivity in polymer composites was evaluated by measuring the isotropic, in-plane and through-plane thermal conductivities of composites containing length-adjusted short and long multi-walled CNTs (MWCNTs). The thermal conductivities of the composites were relatively low irrespective of the MWCNT length due to their high contact resistance and high interfacial resistance to polymer resins, considering the high thermal conductivity of MWCNTs. The isotropic and in-plane thermal conductivities of long-MWCNT-based composites were higher than those of short-MWCNT-based ones and the trend can accurately be calculated using the modified Mori-Tanaka theory. The in-plane thermal conductivity of composites with 2 wt% long MWCNTs was increased to 1.27 W/m·K. The length of MWCNTs in polymer composites is an important physical factor in determining the anisotropic thermal conductivity and must be considered for theoretical simulations. The thermal conductivity of MWCNT polymer composites can be effectively controlled in the processing direction by adjusting the length of the MWCNT filler.     

Die Kalibrierung von Wärmeleitungsvakuummetern. The Calibration of Thermal Conductivity Vacuum Gauges

In many applications in the rough and fine vacuum thermal conductivity gauges are utilized. In order to determine the accuracy of the measuring values modern quality assurance systems require a regular calibration. The calibration laboratory of the German Calibration Service (DKD) at VACUUBRAND GMBH + CO KG features calibration equipment and procedures to calibrate vacuum gauges in the pressure range from 10^‐3 to 1000 mbar. The measuring techniques and calibration procedures are explained for thermal conductivity gauges with digital readouts. Besides general information on the calibration, particularities on thermal conductivity gauges and their effects on the calibration procedure are pointed out. The meaning of measuring deviation and measuring uncertainty and the interpretation of the calibration certificate for the user are discussed.     

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.     

Simultaneous measurement of the thermal conductivity and thermal diffusivity of liquids

In theory, the hot-wire technique for measuring the thermal conductivity of liquids can be used simultaneously to determine the thermal diffusivity. In practice, however, the latter property has so far been determined only with moderate accuracy because of (a) inaccurate bridge balancing due to drift problems, (b) parasitic capacities that delay the heating, and (c) poor precision in the determination of the time. A new measurement procedure has been developed which features (a) a short measuring time, (b) a reduced significance of the balancing technique, (c) a good reproducibility, and (d) a low sensitivity to most error sources. Thermal conductivity and thermal diffusivity results using this procedure, for toluene and n-heptane, which are the generally accepted standards for thermal conductivity, are presented and compared with results from other sources.     

A new approach to the design of a low Si-added Al–Si casting alloy for optimising thermal conductivity and fluidity

The effect of Ni on the thermal conductivity and fluidity of a low Si-added Al–Si casting alloy was investigated. The room temperature thermal conductivity of an Al–2 wt%Si alloy instantly dropped when adding 0.5 wt%Ni, whereas further additions of Ni up to 3 wt% had little influence on the thermal conductivity, which was in the range of 180–185 W/mK. The thermal conductivity was also estimated for the alloys cast at various cooling rates by measuring the electrical conductivity using the Wiedemann–Franz law and increased nearly linearly with an increase in the cooling rates. At such a low level of 2 wt%Si, the castability of the Al–Si alloys, which was evaluated by a fluidity spiral test, was enhanced by the Ni additions, exhibiting the maximum fluidity length at 0.5 wt%Ni.     

Measurements of thermal conductivity of heat-insulating materials for construction

A computer system for measuring the thermal conductivity of heat-insulating materials for construction based on an ITSM-1 meter is described. The thermal flux, temperature difference of the specimen sides, and the thermal conductivity of the material are displayed as functions of time on the computer screen. Translated from Izmeritel'naya Tekhnika, No. 7, pp. 51–53, July, 2000.     

Nano-thermal transport array: An instrument for combinatorial measurements of heat transfer in nanoscale films

The nano-Thermal Transport Array is a silicon-based micromachined device for measuring the thermal properties of nanoscale materials in a high-throughput methodology. The device contains an array of thermal sensors, each one of which consists of a silicon nitride membrane and a tungsten heating element that also serves as a temperature gauge. The thermal behavior of the sensors is described with an analytical model. The assumptions underlying this model and its accuracy are checked using the finite element method. The analytical model is used in a data reduction scheme that relates experimental quantities to materials properties. Measured properties include thermal effusivity, thermal conductivity, and heat capacity. While the array is specifically designed for combinatorial analysis, here we demonstrate the capabilities of the device with a high-throughput study of copper multi-layer films as a function of film thickness, ranging from 15 to 470 nm. Thermal conductivity results show good agreement with earlier models predicting the conductivity based on electron scattering at interfaces.     

The Uncertainty in SCHF‐DT Thermal Conductivity Measurements of Lotus‐Type Porous Copper

Lotus‐type porous metals with many straight pores are attractive for use as heat‐sinks because a large heat‐transfer capacity can be obtained, due to the small diameter of the pores. In order to use lotus‐type porous copper effectively as a heat sink, it is important to know the effective thermal conductivity considering the effect of pores on heat conduction in the material. Since these metals have anisotropic pores, a steady‐state comparative longitudinal heat‐flow method for measuring thermal conductivity, referring to an ASTM standard, is better than other methods. So far, the effective thermal conductivity of lotus‐type porous copper has been measured by using specimens of different thickness (the SCHF‐DT method). In this paper, the uncertainty in the effective thermal conductivity of a specimen measured using this method was evaluated by comparison between numerical analysis and current experimental data. The following conclusions were drawn: 1) The uncertainty showed good agreement with the uncertainty analysis; 2) The contribution of the thermal grease thickness was large, based on a combined standard uncertainty analysis; and, 3) The effective thermal conductivity perpendicular to the pores of lotus copper can be measured within 10% uncertainty by this method.     

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 %.     

Realizing the Accurate Measurements of Thermal Conductivity over a Wide Range by Scanning Thermal Microscopy Combined with Quantitative Prediction of Thermal Contact Resistance

Quantitative thermal performance measurements and thermal management at the micro-/nano scale are becoming increasingly important as the size of electronic components shrinks. Scanning thermal microscopy (SThM) is an emerging method with high spatial resolution that accurately reflects changes in local thermal signals based on a thermally sensitive probe. However, because of the unclear thermal resistance at the probe-sample interface, quantitative characterization of thermal conductivity for different kinds of materials still remains limited. In this paper, the heat transfer process considering the thermal contact resistance between the probe and sample surface is analyzed using finite element simulation and thermal resistance network model. On this basis, a mathematical empirical function is developed applicable to a variety of material systems, which depicts the relationship between the thermal conductivity of the sample and the probe temperature. The proposed model is verified by measuring ten materials with a wide thermal conductivity range, and then further validated by two materials with unknown thermal conductivity. In conclusion, this work provides the prospect of achieving quantitative characterization of thermal conductivity over a wide range and further enables the mapping of local thermal conductivity to microstructures or phases of materials.     

稳态法测算导热系数的原理

分析了测量导热系数传统模型与相关文献中的修正模型的原理与不足,提出一个较为严密的三维传热学模型,利用MATLAB数值模拟验证了其合理性。推导出计算圆柱型试样导热系数的公式,并得到了适合实际应用的简化公式。以真空橡皮盘为例,定量分析了侧壁散热对导热系数测量值的影响程度,给出了试样规格与测算精度的关系曲线。当试样半径与厚度的比值大于28.9时,侧壁散热的影响将小于5%,故可忽略。     

Thermal Conductivity of Cobalt-Based Catalyst for Fischer–Tropsch Synthesis

In this study, the thermal conductivity of cobalt-based catalyst specimens in the temperature range from 160 ^◦C to 255 ^◦C are measured via a steady-state apparatus. The apparatus and procedures are applied to several specimens of cobalt-based catalyst powder compacts. Specimens with different degrees of porosity are produced by pressing cobalt-based catalyst powder with a particle size of (80 to 360) mesh. The thermal conductivity of cobalt-based catalyst powder compacts is investigated as functions of temperature, specimen density, porosity, and powder size. The results indicate that the thermal conductivity of the catalyst specimens increases linearly with temperature and density and is practically independent of the particle size of the powder in an atmosphere of air, while the porosity dependence of the thermal conductivity is inverse to that of density. In addition, the effects of some measuring factors on the thermal conductivity show that the reliability of the thermal conductivity measurements of cobalt-based catalyst specimens are influenced easily by parallelism, specimen roughness, and moisture content, whereas the specimen thickness and water bath temperature have only a slight effect on the reliability.     

Density gradients in aluminium foams: characterisation by computed tomography and measurements of the effective thermal conductivity

The density gradients present in several aluminium foams, produced by the powder metallurgical route, have been analysed by using computed tomography and by measuring the effective thermal conductivity (λ). The method used to measure λ, Transient Plane Source (TPS) technique, allows obtaining values of the local thermal conductivity, i.e. conductivity of a localised zone within the sample. These values have been related to the density of the measured zone, which was obtained from the computed tomography experiments. A power law relationship between local effective thermal conductivity and local density has been obtained.     

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.