测定多孔性固体催化剂颗粒有效导热系数的新方法

提出了一种测定空气中催化剂有效导热系数的方法。该方法简便、易行,实验误差小于5％.在此基础之上用woodside随机分布模型计算了反应条件下催化剂有效导热系数。误差分析表明：该模型误差较小,完全可以用于工程计算。     

多孔固体催化剂的有效导热系数

建立了测定多孔固体催化剂骨架导热系数的实验装置和由此计算催化剂有效导热系数的简化方法，测定并计算了若干工业过程催化剂的有效导热系数，同时，计算了甲烷蒸汽转化催化剂的非等温效率因子。     

钴基催化剂固定床有效导热系数

在165~265℃及常压条件下,采用稳态法测定了气体处于静态时活性组分呈蛋壳型分布的钴基催化剂固定床的有效导热系数,并根据稳态法理论,拟合实验数据获得了固定床有效导热系数与气体导热系数和催化剂导热系数之间的关联式. 实验数据与拟合结果的最大偏差和标准偏差的绝对值分别为1.74%和0.43%. 将实验数据与前人的相关预测模型计算值进行了比较,结果表明,二者吻合良好. 利用气体处于静态时固定床的有效导热系数、Re和Pr,获得了气体流动时固定床径向有效导热系数的计算式.     

影响硬质聚氨酯泡沫塑料导热系数因素的研究及配方优化

详细研究了密度、催化剂、水分、F_(11)用量和聚醚对硬质聚氨酯泡沫导热系数的影响。实验结果表明,密度对导热系数的影响有一峰值,即最佳点,聚醚、催化剂、匀泡剂、F_(11)用量对导热系数都有明显的影响,水分对导热系数影响十分敏感。同时进行了配方优化,得到了最优配方。     

环柱状催化剂内强放热复合反应──传质──传热耦合过程研究(Ⅰ)催化剂曲折因子、有效导热系数的测定

采用经典定态法和改进的单颗粒线反应器法（SPSRM)测定了环柱状环氧乙烷银催化剂的曲折因子,两种方法测定结果十分吻合。提出一种测定固体催化剂颗粒有效导热系数的新方法。该方法简单、方便且不改变催化剂原有的形状及物理结构,可以在催化剂允许使用的任何温度下进行测定,准确度较高。用本方法测定了环氧乙烷合成银催化剂颗粒的有效导热系数,并用于催化剂内部浓度、温度、选择性计算,计算与实验结果吻合良好。     

固定床反应器有效导热系数的研究进展

详细地总结了固定床有效导热系数的研究工作，包括有效导热系数的模型，实验测写方法及应用条件，特别指出了床层径向空隙率和速度分布对模型的影响。还介绍了化学反应对计算模型的影响。     

气体流动条件下钴基催化剂固定床的传热

在气体流量4~8 Nm3/h、气体分布器进口温度190~210℃、加热管壁温约240℃的条件下,对气体流动时活性组分呈蛋壳型分布的钴基催化剂固定床的传热进行了实验研究,建立了二维拟均相传热模型,利用正交配置法和Levenberg-Marquardt法对其求解,得到了钴基催化剂床层径向有效导热系数及壁给热系数的关联式,并将传热参数与由气体处于静态时固定床的有效导热系数计算而得的固定床传热参数值进行了比较,在气体入口温度范围内考察了其对固定床传热参数的影响. 结果表明,实验所得传热参数与文献值的最大偏差绝对值均在15%以内.     

环柱状催化剂内强放热复合反应──传质──传热耦合过程研究(Ⅰ)催化剂曲折因子、有效导热系数的测定

采用经典定态法和改进的单颗粒线反应器法（SPSRM)测定了环柱状环氧乙烷银催化剂的曲折因子,两种方法测定结果十分吻合。提出一种测定固体催化剂颗粒有效导热系数的新方法。该方法简单、方便且不改变催化剂原有的形状及物理结构,可以在催化剂允许使用的任何温度下进行测定,准确度较高。用本方法测定了环氧乙烷合成银催化剂颗粒的有效导热系数,并用于催化剂内部浓度、温度、选择性计算,计算与实验结果吻合良好。     

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。     

水泥石导热系数的计算模型

测试了不同水灰比、不同养护龄期水泥石的导热系数,并对比了并联模型、串联模型、Maxwell模型、Mori-Tanaka模型、有效介质理论模型和Self-consistent模型对水泥石导热系数的预测效果。利用分子动力学方法计算了水泥石中各相的导热系数。结果表明:水泥石的导热系数随着养护龄期和水灰比的增大而减小。SC模型适用于不同水灰比和养护龄期水泥石导热系数的计算,其计算结果与试验值的相对误差在0.3%～4.7%之间。Maxwell模型和MT模型可以用于对水灰比较大且养护龄期较长的水泥石的导热系数进行计算。     

Thermal Diffusivity/Conductivity of Magnesium Oxide/Silicon Carbide Composites

SiC-particle-reinforced MgO composites have been fabricated by hot pressing, and the thermal diffusivities of the composites measured in the temperature range 200–1000°C using a laser flash technique. The thermal conductivity of the composites was calculated by multiplying the diffusivity with density and with heat capacity. The Eshelby inclusion model has been examined, and an equation suitable for particulate composites with porosity has been derived using the multiphase Eshelby model. The model also considers the interfacial thermal condition. Good agreement was obtained between the predictions and the experimental results of the thermal conductivity of the composites, even for various levels of porosity in the composites. Crystal defects, observed in the composites, influenced the thermal conductivity, resulting in a deviation from isothermal interfacial condition. This was reflected in the interfacial thermal parameter,β used in the modeling, and the predicted value of β was in the range of 3–10, depending on the thermal conductivity of SiC used for the calculations.     

Porosity and pore size distribution influence on thermal conductivity of yttria-stabilized zirconia: Experimental findings and model predictions

Porous yittria-stabilized zirconia is an important advanced ceramic material for technological applications. One of the most important characteristics of this material is low thermal conductivity, which is greatly influenced by the presence of pores into the microstructure. In fact, air trapped in the pores represents a better thermal insulator. The role of the pore volume fraction on porous material characteristics has been extensively studied. On the other hand, the influence of the structure disorder, the pore size range and pore size distribution have been studied much less. In this study, an intermingled fractal model capable of relating thermal properties of ceramic materials and their pore microstructure has been proposed. Model predictions are found confirming the experimental data fairly well, even better than the others models available in the literature.     

PP/AlN复合材料导热机理研究

以氮化铝(AlN)粉末、聚丙烯(PP)为原料,通过共混-模压法制备了PP/AlN导热复合材料,并对其导热性能进行检测。研究发现,该复合材料的导热系数与AlN添加量之间不是线性关系而是呈幂函数关系,与介电逾渗理论基本吻合。根据检测数据并参考介电逾渗理论,提出了导热逾渗模型,并利用该模型和其他导热预测模型对PP/AlN复合材料的导热系数进行了计算。结果表明:复合材料的导热系数随AlN质量分数的增加呈幂函数增加趋势;实际检测结果与导热逾渗模型的预测结果基本相符,使该理论得到了验证。     

Thermal conductivity of traditional ceramics. Part I: Influence of bulk density and firing temperature

The thermal conductivity of traditional ceramics is known to be a function of their porosity or bulk density. However, the scatter in the thermal conductivity–bulk density data in certain studies, particularly when data from industrially processed brick are involved, suggests that thermal conductivity depends, apart from porosity, on other characteristics such as phase composition, microstructure, humidity or the presence of soluble salts.A red-firing clay used in brick manufacture has been used in this study with a view to systematising the impact of the different variables that could influence thermal conductivity and mechanical strength. This first paper presents the results obtained when the dry bulk density of the pieces and their firing temperature were modified.It was confirmed that thermal conductivity did not solely depend on the total porosity of the fired pieces, but that pore size distribution and pore interconnectivity need to be considered, which depend on the degree of firing attained, and may also be influenced by the phases present in the pieces, whose content and/or composition could vary with firing temperature.     

High porous yttria-stabilized zirconia with aligned pore channels: Morphology directionality influence on heat transfer

High porous yttria stabilized zirconia with unidirectionally aligned channels is used in engineering applications with extremely low thermal conductivity. This property is strongly influenced by microstructure features such as pore volume fraction, pore size distribution, random porous microstructure and pore morphology directionality. Although several models are reported in the available literature, but their analytical formulas are formalised for homogeneous structures or they are based on proportion between solid and fluid phases. These differences from real microstructures cause significant computational errors especially when thermal conductivity changes as the function of the measurement direction (parallel or perpendicular). In this context, the application of an intermingled fractal unit's procedure capable of reproducing porous microstructure as well as predicting thermal conductivity has been proposed. The results are in agreement with experimental ones measured for parallel and perpendicular directions and suggest improving the formalisation of fractal modelling in order to obtain an instrument of microstructure design.     

Equilibrium,interfacial and transport properties of n-alkanes: Towards the simplest coarse grained molecular model

In this work, using molecular dynamics simulations, we have investigated how simple could be a coarse grained molecular model yielding simultaneously equilibrium densities, surface tensions and transport properties of some n-alkanes (from methane to n-decane) along the vapour–liquid equilibrium curve. For that purpose, as an initial model, the fully flexible Lennard–Jones Chain (3 “molecular” parameters) model has been chosen. Using this simple molecular model, good results have been obtained on equilibrium properties of all tested n-alkanes despite a systematic slight overestimation of critical temperatures, critical pressures and surface tensions. In addition, concerning transport properties, good results have been obtained for methane and n-butane except for thermal conductivity in the gas state. For n-heptane and n-decane it has been found that thermal conductivity is systematically underestimated while viscosity is well estimated except at low temperatures. Concerning thermal conductivity, this misevaluation can be corrected if the zero-density thermal conductivity is known. Concerning shear viscosity, it is found that an additional “rigidity” fourth parameter is required to improve the results when dealing with the longest chains at the lowest temperatures.     

Thermal conductivity of highly oriented polyethylene

We have measured the thermal conductivity of oriented polyethylene both along and perpendicular to the draw direction for draw ratio λ between 1–25 and in the temperature range of 120 to 320K. The results for λ ? 5 have been analysed in terms of the modified Maxwell model while the further increase of thermal conductivity along the draw direction at higher λ has been explained by the Takayanagi model. The Young's modulus and thermal conductivity along the draw direction for the sample with λ = 25 were found to be 64 GN/m² (at 220K) and 140 mW/cm K (at 300K), respectively, which are extremely high values for polymers. This material, which is a good electrical insulator and yet has a high thermal conductivity, may be useful in electrical applications requiring large dissipation of heat.     

挤塑板表面结构对导热系数的影响

通过对几种不同表面结构类型的挤塑聚苯乙烯泡沫塑料（XPS）板的导热系数进行检测并对数据进行分析和讨论。结果表明,表面开槽对XPS导热系数的影响较小,单面去除表皮次之,而双面去除表皮会明显降低XPS的导热系数。     

Modelling and evaluating thermal conductivity of porous thermal barrier coatings at elevated temperatures

Thermal conductivity of various porous thermal barrier coatings (TBCs) used at elevated temperatures for gas turbines has been evaluated using the proposed six-phase model. These TBCs rely on microstructural properties and yield different types of porosities. This paper studies the thermal conductivity of TBCs based on microstructural features to evaluate the effect of different types of porosities on thermal conductivity. The first part of this paper investigates the microstructural characterization of various TBCs using image analysis (IA) technique. The second part of this paper evaluates the thermal conductivity using the image analysis. The volumetric fraction of porosities along with their orientation, shape and morphology, shows a considerable impact on the overall thermal conductivity of TBCs. The proposed six-phase model can predict thermal conductivity of porous TBCs with a good agreement with the measured values. The model results can help to better understand the effect of microstructural changes on thermal conductivity and can provide useful guide to fabricate TBCs with low thermal conductivity.     

Thermal Conductivity Coefficients of Unidirectional Fiber Composites Defined by the Concept of Interphase

In this paper, the thermal conductivity coefficients of unidirectional composites have been estimated. In the present analysis, a model which takes into account the influence of the boundary interphase has been proposed. The thermal conductivity coefficients of the composite were calculated by using this concept to determine the role of the interphase which mainly depends on the quality of adhesion between fibers and matrix. The interphase matter is the part of the polymer matrix lying on the close vicinity of the fiber bounding surface. It has been primarily assumed that the interphase is inhomogeneous with thermophysical properties varying from the fiber surface to the matrix. Five laws of variation have been taken into consideration in order to derive closed form expressions for the thermal conductivity coefficients in which the role of the interphase layer occurs, possessing properties different from those of the constituent phases. A thermal analysis method known in the literature has been adopted in order to find the extent of the interphase layer. According to this viewpoint, theoretical expressions in order to calculate the thermal conductivity coefficients of the glass fiber reinforced composite materials were derived taking into consideration the interphase layer.