耐硫甲烷化催化剂的有效导热系数研究

在常压空气气氛下采用稳态法测试了KD306型耐硫甲烷化催化剂的有效导热系数,运用Woodside随机模型,建立了反应状态下有效导热系数的计算模型。研究表明,该催化剂有效导热系数较大,温度、压力影响明显,组成影响较小。     

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。     

串联模型法测量泡沫塑料导热系数

采用串联模型热流计法,即通过叠加试样间接测量的方式,对硬质聚氨酯泡沫塑料、橡塑泡沫塑料及挤塑聚苯乙烯泡沫塑料在平均温度10℃、15℃、25℃下的导热系数进行了测试,并分析比较了导热系数测试值与模型计算值。结果表明:在不同平均温度及材料条件下,导热系数的串联模型计算值与测试值的误差均较小,因此该串联模型可用于薄层材料导热系数的测试。     

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。     

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。     

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。     

有机物混合液导热系数的预测

文章根据液体物质的导热系数与密度的关系,导出了估算有机物混合液导热系数的计算模型。利用该模型计算了53个体系369个数据点的二元有机物混合液导热系数,计算值与实验值的总平均相对偏差为1.434%,计算值与实验数据吻合较好,计算准确性优于文献方法;文章方法简单方便,只需要混合液各组分的临界温度、临界体积和导热系数数据,就可以直接预测各种温度和组成的有机物混合液的导热系数。     

有机物混合液导热系数的估算

通过对液体导热系数与密度关系的分析研究,提出了估算有机物混合液导热系数的计算模型;利用该模型计算了55个体系377个数据点的二元有机物混合液导热系数,计算值与实验值的总平均相对偏差为1.48%,计算值与实验数据吻合很好,计算准确性优于文献方法;本文方法简单方便,只需要混合液各组分的导热系数数据,就可以直接预测各种温度和组成的有机物混合液的导热系数。     

用并联模型法测定泡沫塑料的导热系数

稳态热流计法操作简单,广泛用于测量保温材料的导热系数。但由于仪器设备和方法的限制,难以测试异型材料的导热系数。分别采用并联模型法和直接测量法分析了挤塑聚苯乙烯泡沫、硬质聚氨酯泡沫、橡塑泡沫在平均温度10、15、25℃下的导热系数。结果表明:在不同平均温度和不同材料中,采用并联模型法所计算的导热系数与测试结果误差较小,说明并联模型法可用于不规则泡沫塑料导热系数的测试。     

有机物水溶液导热系数的关联

根据对有机物水溶液导热系数影响因素的分析,在Horvath液体导热系数关系式的基础上,导出了估算有机物水溶液导热系数的计算模型;利用该模型计算了14个体系中447个数据点的不同温度和组成的二元水溶液导热系数;结果表明,计算值与实验数据吻合很好,其与实验值的总平均相对偏差为1.03％,计算准确性优于文献方法。本文计算方法简单方便,只需知道水溶液各组分的临界温度、临界体积和导热系数数据,就可以直接预测各种温度和组成的有机物水溶液混合物的导热系数。     

混合填充复合材料热导率方程的推导

混合填充复合材料的导热特性好于单一填充。根据碳纳米管与纳米片状石墨在高分子基材中的分布形态, 将碳纳米管与纳米片状石墨的"桥状搭接"结构作为等效基材, 未搭接的"游离态"碳纳米管作为填料, 利用串并联热阻模型和Maxwell-Garnett等效介质法建立了混合填充复合材料的导热模型, 并通过数量级分析对热导率方程进行了简化。结果表明, 在混合填料质量分数不变的情况下, 等效热导率随纳米片状石墨的增多呈现先增加后减少的趋势, 表现出明显的协同效应;在质量分数配比不变的情况下, 等效热导率随混合填料的质量分数增大而增大。     

固液相变数学模型中有效热导率

在一维固液相变数学模型中有效热导率计算公式的研究基础上,根据理论分析和实验数据,对一维有效热导率进行了修正,并把有效热导率计算公式应用到二维相变问题中.通过对等热通量和等壁温边界条件的仿真计算结果与实验数据相比较,说明了本文的有效热导率计算方法的合理性.     

EFFECTIVE THERMAL CONDUCTIVITY OF BINARY MIXTURES AT HIGH SOLID TO GAS CONDUCTIVITY RATIOS

The effective thermal conductivity of single size and binary mixtures of packed particle beds with stagnant gas at high solid/gas conductivity ratios is determined by a deterministic, unit cell approach. The model results are shown to be in good agreement with experimental data for various gas pressures and solid to gas thermal conductivity ratios up to 1300. A set of correlations for effective conductivity of binary mixtures as a function of gas pressure and particle size is derived. The effect of particle swelling on the effective conductivity of binary mixtures is studied by performing a parametric study of the contact area between the particles     

Heat transfer in nanoparticle suspensions: Modeling the thermal conductivity of nanofluids

This work reviews experimental data and models for the thermal conductivity of nanoparticle suspensions and examines the effect of the properties of the two phases on the effective thermal conductivity of the heterogeneous system. A model is presented for the effective thermal conductivity of nanofluids that takes into account the temperature dependence of the thermal conductivities of the individual phases, as well as the size dependence of the thermal conductivity of the dispersed phase. We demonstrate that this model can be used to calculate the thermal conductivity of nanofluids over a wide range of particle sizes, particle volume fractions, and temperatures. The model can also be used to validate experimental thermal conductivity data for nanofluids containing semiconductor or insulator particles and confirm the size dependence of the thermal conductivity of nanoparticles. © 2010 American Institute of Chemical Engineers AIChE J, 2010     

开孔泡沫金属复合材料有效热导率的研究进展

有效热导率是开孔泡沫金属复合材料热传输热性的重要参数,基于三维结构的复杂性,从边界模型和晶胞分析模型两个方面出发,较为全面地概述了有效热导率的研究现状。指出边界模型以均质化方法宏观分析热传导问题而忽略了微观孔结构的影响,重点阐述晶胞分析模型中立方体模型和开尔文模型的经验相关性分析方法,指出其关键点在于以孔隙率形式将多孔结构形状参数拟合成可调参数表达式。此外,3D断层扫描与数值模拟相结合,阐述lattice-Boltzmann方法对开孔泡沫结构的研究,突出真实孔结构对有效热导率的影响和规律。展望后期研究重点是经验相关模型的精确拟合方式及特征关联式的统一化,高精度数值模拟计算中的简化对比分析模型。     

Effect of particle size on the thermal conductivity of nanofluids containing metallic nanoparticles

A one-parameter model is presented for the thermal conductivity of nanofluids containing dispersed metallic nanoparticles. The model takes into account the decrease in thermal conductivity of metal nanoparticles with decreasing size. Although literature data could be correlated well using the model, the effect of the size of the particles on the effective thermal conductivity of the nanofluid could not be elucidated from these data. Therefore, new thermal conductivity measurements are reported for six nanofluids containing silver nanoparticles of different sizes and volume fractions. The results provide strong evidence that the decrease in the thermal conductivity of the solid with particle size must be considered when developing models for the thermal conductivity of nanofluids.     

Thermal conductivity of nanofluids: Effect of Brownian motion of nanoparticles

The model of Xuan et al. (2003) for the thermal conductivity of nanofluids in which Brownian motion effect is added to the classical Maxwell's equation is discussed. The model is revised. Also, a different model is given and found to yield the same expression for the effective thermal conductivity after amending Xuan et al.'s model. The findings do not support the claim that Brownian motion of nanoparticles has a significant impact on thermal conductivity. Also, nanoparticles clustering is found to have a very minor effect on the effective thermal conductivity of nanofluids; however, the analysis may not be appropriate to draw conclusions about the impact of clustering. © 2015 American Institute of Chemical Engineers AIChE J, 61: 2368–2369, 2015     

Multiscale Genome Modeling for Predicting the Thermal Conductivity of Silicon Carbide Ceramics

Silicon carbide (SiC) ceramics have been widely used in industry due to its high thermal conductivity. Understanding the relations between the microstructure and the thermal conductivity of SiC ceramics is critical for improving the efficiency of heat removal in heat sink applications. In this paper, a multiscale model is proposed to predict the thermal conductivity of SiC ceramics by bridging atomistic simulations and continuum model via a materials genome model. Interatomic potentials are developed using ab initio calculations to achieve more accurate molecular dynamics (MD) simulations. Interfacial thermal conductivities with various additive compositions are predicted by nonequilibrium MD simulations. A homogenized materials genome model with the calculated interfacial thermal properties is used in a continuum model to predict the effective thermal conductivity of SiC ceramics. The effects of grain size, additive compositions, and temperature are also studied. The good agreement found between prediction results and experimental measurements validates the capabilities of the proposed multiscale genome model in understanding and improving the thermal transport characteristics of SiC ceramics.     

The use of drying experiments in the study of the effective thermal conductivity in a solid containing a multicomponent liquid mixture

The effective thermal conductivity of a porous solid containing multicomponent liquid mixtures has been studied. To achieve this, the liquid composition, liquid content and temperature distributions have been measured in a cylindrical sample dried by convection from the open upper side and heated by contact with a hot source at the bottom side. A quasi-steady state reached at high source temperatures permits to calculate the total heat flux from temperatures measured on the surface and the gas stream. The simulations performed and compared with experimental data made it possible to estimate the adjusting geometric parameter of Krischer's model for the effective thermal conductivity. The effective thermal conductivity has been widely studied for two-phase systems, mostly with regard to thermal insulation elements. The calculation of this transport parameter includes the contribution to heat transfer of the evaporation–diffusion–condensation mechanism undergone by the multicomponent mixture. The influence of liquid composition and temperature on the thermal conductivity due to the evaporation–diffusion–condensation mechanism and the effective thermal conductivity is described. The results reveal that in this case the resistance to heat transfer seems to correspond to a parallel arrangement between the phases.     

Effect of point defects on the thermal conductivity of Sc2O3-Y2O3 co-stabilized tetragonal ZrO2 ceramic materials

In this paper, the reduction mechanism in thermal conductivity of a series of Sc₂O₃-Y₂O₃ co-stabilized tetragonal ZrO₂ ceramics is systematically discussed. The thermal conductivity is approximately 20–28% lower than that of 6–8 wt.% yttria-stabilized zirconia (YSZ). A phonon scattering model, on account of the influence of oxygen vacancy variation and cation mass fluctuation, is optimized and utilized to depict the thermal conductivity of these materials. For the samples with the same amount of oxygen vacancy, Sc³⁺ is more effective in lowering thermal conductivity than Y³⁺ due to the large mass difference with Zr⁴⁺, as evidenced by the scattering model and phonon vibrational density of states. The experimental and calculation results suggest that this optimized model is proved to be more effective in predicting the thermal conductivity of binary or multiple rare earth oxides co-doped tetragonal ZrO₂ and guiding the compositional design of thermal barrier materials.