加压下液体物质导热系数的关联和预测

在采用查表法估算加压下液体导热系数的Missenard法的基础上,利用液体物质导热系数的文献数据,导出了估算加压下液体导热系数的计算模型.利用该模型计算了加压下18种液体物质313个数据点的导热系数数据,计算值与实验值的总平均相对偏差为3.08％,计算值与实验数据吻合很好,计算准确性优于文献方法;文中方法简单方便,只需...     

Numerical simulation of the effect of moisture on the thermal conductivity of porous ceramic materials

A simulation model to analyze the influence of moisture content on the thermal conductivity of porous ceramic materials is developed based on the numerical integration of the energy equation. The experimental technique employed for thermal conductivity measurements is the hot wire parallel technique. The numerical model proposed is checked by evaluating the thermal conductivity of a hypothetical porous ceramic material containing different concentrations of water in its structure. The behaviour of the thermal conductivity as a function of temperature, as predicted by the model proposed in this work was experimentally verified by the authors for an unfired refractory concrete. ©     

Experimental evidence of a moisture clog effect in cement-based materials under temperature

This study is an original contribution to the understanding of the hydraulic behaviour of cement-based materials when subjected to temperature rises. Permeability is measured continuously during heating by injecting inert gas into a sample at homogeneous temperature. Using a confining cell especially designed in our laboratory, the sample is submitted to a constant heating rate, up to 200 °C, superimposed to hydrostatic pressure (at ca. 5 MPa). In parallel with a normalised CEM II mortar (water-to-cement ratio (W/C) of 0.5), a CEM V-cement-based concrete, used in nuclear waste storage applications, is studied. For normalised mortar, gas retention is evidenced, depending on the sample size (scale effect), water saturation level S_w, and heating rate. For dry normalised mortar, permeability may be divided by two during heating. In conjunction with thermo-gravimetry analysis (TGA) results, such evolution is attributed to the dehydration of C–S–H around 150 °C. Indeed, mass loss after heat cycling is substantially higher than that due to free water release solely: mortar loses structural, bound water during the process. For partially-saturated and long mortar samples, a gas retention phenomenon is recorded when heating at a rate of ca. 4.9 °C/min. Our analysis is that free water inside the macropores, as well as bound water released from the C–S–H, dilates or vaporizes, and obstructs the interconnected porous network. Due to moisture clogging, no more gas is allowed through the material pore network: a so-called gas retention phenomenon occurs. Most interestingly, although loosing structural water like normalised mortar, yet over a wider temperature range, dry CEM V concrete displays good temperature resistance, as its permeability remains constant during heating. For highly partially-saturated concrete, a gas retention effect is recorded. As a conclusion, observed phenomena at the laboratory scale testify of potentially strong gas retention effects upon engineering structures subjected to temperature gradients over time. Indeed, quite low temperature rises (and heating rates) are able to induce moisture clogging inside partially-saturated materials. It is also concluded that cement-based material composition, i.e. bound water release ability, is influential in gas transport phenomena under temperature.     

On the thermal conductivity of granular materials

Stationary heat transfer in a granular material consisting of a continuous medium containing spherical granules of other substances is considered under the assumption that the spatial distribution of granules is random. The effective thermal conductivity characterizing macroscopic heat transfer in such a material is expressed as a certain function of the conductivities and volume fractions of the medium and dispersed substances.For reasons of mathematical analogy all the results obtained for the thermal conductivity are valid while computing the effective diffusivity of some admixture in granular materials as well as for evaluation of the effective electric conductivity or the mean dielectric and magnetic permeabilities of granular conductors and dielectrics.     

聚合物基热界面材料与导热性能研究进展

随着电子产品的小型化、集成化和功能化发展,功率密度及热流密度急剧上升,器件内巨大的散热和温压压力使电子设备的寿命和可靠性受到影响,因此对器件在运行过程中如何有效散热提出了更为苛刻的要求。开发及使用高性能导热基复合材料（热界面材料,TIM）降低接触热阻是解决电子设备散热问题的有效途径之一,热界面材料创新与优化备受关注。本文从基本的导热机理出发,阐述聚合物基热界面材料结构及导热强化方面最新进展,讨论导热填料和聚合物基体对复合材料性能的影响。重点对微纳结构的导热强化（协同）作用、构筑3D高导热微结构、导热填料和基质间的界面微结构和导热互穿网络结构等进行讨论,为设计高性能导热结构、制备开发新型高性能TIM提供参考。     

Calorimetric thermal conductivity measurement for high-temperature materials

A K1952 instrument has been upgraded to determine the thermal conductivities of materials by the GOST 12170 stationary method. The application of that method has been extended to the determination of thermal conductivity for industrial forms of refractory materials and for research in material science, design, and thermal insulation calculation. The K1952 system has been used in testing standard specimens. It has been confirmed that the parameter measurements conform to the technical documentation for standard specimens. A certificate has been obtained to confirm the type of means of measurement RU. E.32.001.A No. 30197, which was issued by the Federal agency on technical regulation and metrology. Translated from Novye Ogneupory, No. 2, pp. 47 – 49, February, 2009.     

Correlation of aqueous-physical, structural-mechanical, and thermophysical properties of moist disperse materials

It is shown that the cohesiveness and plastic strength of moist materials and their thermophysical and drying properties are determined by the ratio of capillary-mobile and capillary-immobile moisture forms and natural properties of materials which can be best estimated based on the least capillary moisture or the maximum molecular moisture capacity which are the most significant aqueous-physical parameters of materials. Formulas are proposed for the calculation of the dependence of cohesiveness and plastic strength of materials on their moisture content and drying sensitivity, as well as formulas for the calculation of thermophysical properties of moist materials. Translated from Steklo i Keramika, No. 5, pp. 17–21, May, 2000.     

炭砖的导热性能及其影响因素的研究

应用计算机运控的激光热导仪,对不同化学成分、密度和热历史的炭砖的导热系数进行了对比分析和研究,提出了一个由导热性能数据判断炭砖可继续使用的新方法。     

A study of thermal conductivity of structural ceramic materials. Part I. State of research of thermal conductivity of structural materials

At the present time, experiment is a reliable method for studying the thermal conductivity of new ceramic materials and especially refractories. However, the range and possibilities of existing devices do not meet the requirements for measuring thermal conductivity, especially at a high temperature. At very high thermal loads under the conditions of formation of surface columnar crystal structures, thermoelastic stresses, disturbances in vibration of the elementary lattice, and other phenomena, the thermal conductivity can be a function of the temperature drop. The present paper concerns the physical fundamentals of heat conduction in current ceramic materials and refractories based on MgO, A1₂O₃, and Si₃N₄. The classical stationary and nonstationary methods for determining thermal conductivity are considered. Special attention is devoted high-temperature processes and the difficulties arising in this case. It is recommended to solve high-temperature problems by using methods based on solving inverse problems of heat conduction     

多孔泡沫介质有效导热系数的研究

在平面热阻模型基础上,考虑多孔介质固、流两相导热系数、孔隙率以及孔隙分布等因素的影响,通过引入倾斜角α,提出了一个预测多孔泡沫介质有效导热系数的数学模型。通过对本文模型的预测结果与国内外有关多孔泡沫介质有效导热系数的实验数据以及其他预测模型的预测结果进行比较,验证了本文所得数学模型的准确性。     

Hydrogenation induced deformation mode and thermal conductivity variations in graphene sheets

In this study, we adopt molecular dynamics simulation and first principles theory calculation to investigate the deformation modes of graphene sheets induced by patterned hydrogenation stripes, as well as thermal conductivity variation with respect to the doping density and deformation modes. We demonstrate that the deformation modes can be controlled by the hydrogenation patterning parameters. Both the doping density and morphology contribute to the thermal conductivity variation of the graphene sheet. With the control of hydrogenation patterning parameters, desired deformation modes and thermal conductivity of graphene can be achieved.     

High-Temperature tests of heat-insulating refractory materials for thermal conductivity

Specialists of D. I. Mendeleev Russian University of Chemical Engineering have created an installation for determining the thermal conductivity of heat-insulating refractory materials in the range of 20–1000°C using a measuring cross. The data obtained for materials tested by the steady-flow method and the hot-wire method (ISO 8894-1:1987 (E)) differ by no more than 12%.     

高导热绝缘材料的研究进展

主要介绍了高导热绝缘材料的应用以及导热填料对高导热绝缘材料性能的影响因素。重点介绍了填料种类、尺寸、表面处理和加入量对于导热绝缘高聚物性能的影响,并分析了高导热绝缘材料的未来研究方向。     

The effective thermal conductivity of three-dimensional reticulated foam materials

In this paper, the effective thermal conductivity k _eff of three-dimensional (3D) reticulated SiC foams were investigated through experimental and numerical methods. The results showed that the k _eff of SiC foams increases as the volume fraction f increases from 30% to 50%. However, there are no systematic changes detected in k _eff when the cell size of the foam varies at a fixed volume fraction. The k _eff of SiC foams as a function of f was obtained. Compared the experimental results with the calculated ones, it indicated that the outcome can be widely applied in estimating the effective thermal conductivity of other foam materials.     

Enhanced thermal conductivity and isotropy of polymer composites by fabricating 3D network structure from carbon-based materials

Graphene-based composite is promising as thermal interface material (TIM) due to its outstanding thermal properties. However, there are some bottlenecks to excellent performance, such as agglomeration of particles and undesirable voids between nanoplatelets. In this work, a composite with three-dimensional (3D) thermally conductive network has been assembled, which combines three kinds of nanofillers varying geometric dimensions. Thermal conductivity (TC) of composite with graphene nanoplatelets (GNPs) and carbon-nanotubes (CNTs) at a weight ratio of 3:1 is around 9% higher than that of GNP-based composite. By the introduction of carbon spheres (CSs), the TC is further increased by 28%. The enhanced thermal property further demonstrated by FLIR infrared camera is attributed to the formation of 3D heat conduction paths by GNPs, CNTs, and CSs, where the GNPs play the role of thermally conductive backbones. The other two components are introduced to attenuate the aggregation and strong thermal anisotropy. Moreover, the TC is confirmed nearly isotropic, which is different from most graphene-based TIMs because of the in-plane alignment. Our results indicate that the apparent synergy endows this 3D nanofiller great potential for heat dissipation applications requiring heat removal in two directions.     

Enhanced modeling of moisture equilibrium and transport in cementitious materials under arbitrary temperature and relative humidity history

This paper focuses on behaviors of moisture dispersed in nano‐macro scale pores under various temperature and relative humidity conditions. The authors formulated an equilibrium relationship between liquid and vapor phases and a moisture flux driven by pore pressure, vapor pressure and temperature gradients. In addition, liquid and interlayer water were measured separately by ethanol in order to reveal each temperature sensitivity in saturation‐humidity paths. Based on the experiments, a modified hysteresis model for moisture isotherm was proposed. Verifications with experimental data showed that the proposed method can simulate moisture behaviors under various temperature conditions.