A novel method to determine effective thermal conductivity of porous materials

1 Introduction Due to some unique structure and characteristics, the porous material behaves as afunctional material and is finding more and more applications in a variety of fields suchas aviation, chemistry and energy[1]. In such cases, the effective thermal conductivity ofthe porous materials is a vital parameter that dominates application performances. Gen-erally speaking, the effective thermal conductivity can be measured experimentally, butin some cases (for example the stuffing is l…     

Determination of permeability using fractal method for porous media

A theoretical formulation was developed to express permeability as a function of different fractal dimensions and other scales for porous media . The effective fractal void ratio, the spectral dimension and the fractal dimension of particle mass distribution were introduced. The permeabilities for different soils in China are calculated. The predicted permeability for rice soil was compared with the measured data available in literature.     

木材横纹有效导热系数的分形模型

提出了一个二维的分形模型来计算木材横纹有效导热系数.通过分析木材试样的扫描电镜照片，研究了木材横纹剖面的多孔结构特征，采用盒维数法计算了其分形维数.通过分析单一木材细胞的导热过程，采用热阻模拟方法分别推导了弦向和径向有效导热系数的表达式.实验得到各种木材的纤维多孔结构的分形维数约为1.4，由木材纤维孔隙率与分形维数的关系得到了有效导热系数随分形维数变化的表达式.利用分形模型对木材径向有效导热系数进行了计算，并与实验测量结果和文献中的数据进行了比较.结果表明，此分形模型可以对各种木材的横纹有效导热系数进行有效的预测，而且可以推广到不同含水率的情形.     

堆积型含湿多孔介质导热系数测试实验研究

以砂子模拟堆积型多孔介质,采用Hot Disk热常数分析仪（TPS 2500）对不同含湿率砂的有效导热系数进行测量和实验研究。研究发现,非饱和含湿砂有效导热系数随含湿率的增加而增大。低含湿率（体积含湿率低于25％）情况下,砂子的有效导热系数难以准确测得,其主要原因是测试过程中,由于加热影响,贴近探头附近的水分因蒸发扩散而逐渐减少,探头周围试样构成不能保持恒定,导致测试环境持续发生变化。     

大孔隙对多孔介质导热性能影响的数值分析

采用有限体积方法求解Laplace方程,对非均匀多孔介质中大孔隙对导热性能的影响规律进行数值分析。研究结果表明,有效导热系数随着大孔隙的形状、排列方式、连通性和方向的不同呈现出很大的波动性,其中大孔隙的连通性和方向对多孔介质导热性能的影响尤其严重。研究结果可为非均匀多孔介质导热性能预测模型的改进提供参考依据。     

碱木质素基聚氨酯泡沫塑料的制备和性能表征

通过热重失重率（TG）和失重速率（DTG）曲线得,碱木质素基聚氨酯泡沫塑料起始分解温度和峰值分解温度分别为250℃和370℃,结果表明,材料热稳定性、保温性能较好。通过压缩试验,碱木质素基聚氨酯泡沫塑料的10％压缩强度蛳为203kPa。通过对加载后碱木质素基聚氨酯泡沫塑料进行扫描电镜分析,探讨增强机理。     

Determination of thermal conductivity for particulate materials

Ｆｏｒｔｈｅｍｅａｓｕｒｅｍｅｎｔｓｏｆｐａｒｔｉｃｕｌａｔｅｍａｔｅｒｉａｌｓａｍｏｄｉｆｉｅｄｈｏｔｗｉｒｅｔｅｃｈｎｉｑｕｅｗａｓｕｓｅｄ．Ｔｈｅｃｈｏｉｃｅｏｆｔｈｉｓｔｅｃｈｎｉｑｕｅｗａｓｍａｄｅｂｙｃｏｎｓｉｄｅｒｉｎｇｔｈａｔｔｈｅｔ...     

Determination of thermal conductivity of magnesium-alloys

Ｔｈｅｒｍａｌｃｏｎｄｕｃｔｉｖｉｔｙａｎｄｔｈｅｒｍａｌｄｉｆｆｕｓｉｖｉｔｙａｒｅｃｒｕｃｉａｌｔｏｍｅｔａｌｌｉｃｍａｔｅｒｉａｌｓａｓｔｈｅｙａｆｆｅｃｔｔｈｅｈｅａｔｔｒａｎｓｆｅｒｒａｔｅｉｎｔｈｅｐｒｏｃｅｓｓｉｎｇｐｒｏｃｅｓｓａｎｄｔｈｅｒｅｆｏｒｅ,ｉｎｆｌｕｅｎｃｅｔｈｅｔｈｅｒｍｏｐｈｙｓｉｃａｌｐｅｒｆｏｒ ｍａｎｃｅｏｆｔｈｅｍｅｔａｌｐｒｏｄｕｃｔｓ .Ｔｈｅｒｅｆｏｒｅ ,ｉｔｉｓｏｆｉｍｐｏｒｔａｎｃｅｆｏｒｍｅｔａｌｌｕｒｇｉｃａｌｉｎｄｕｓｔｒｙｔｏｄｅｔｅｒｍｉ…     

比较法测取导热系数

自行设计了一种的测取导热系数的实验装置 ,对一些复杂混合物进行导热系数的测定 ,测定结果较好 ,并且在生产中得以应用     

金属蜂窝结构有效热导率的预报与实验研究

建立了蜂窝夹芯结构有效热导率的数值计算模型,算例表明预报结果与实际值吻合很好.设计并制造了有效热导率的测试设备,对A l蜂窝样件进行了稳态热传导实验测试,结果表明,在平均温度高于150℃时与数值结果的相对误差不超过7%,所建立的分析和实验方法能够实现对蜂窝结构热性能的评价分析.     

Determination of relationships between thermal conductivityand material properties of rocks

Energy transfer between the adjacent parts of rocks in underground mines is widely influenced by the thermal conductivity of rocks. The relationships between the thermal conductivity and some material properties of rocks such as the uniaxial compressive strength, unit mass, tensile strength, cohesion, Young‘s modulus, point load strength, Schmidt rebound hardness, Shore scleroscope hardness and toughness strength were investigated. The statistical analysis of the data obtained in laboratory tests shows that the thermal conductivity increases with increasing the uniaxial compressive strength, unit mass, tensile strength, cohesion, Young‘s modulus, point load strength, Schmidt rebound hardness and Shore scleroscope hardness, and decreases with increasing the toughness strength.     

Investigation on the thermal conductivity of HDPE/MWCNT composites by laser pulse method

Thermal conductivity (TC) of high density polyethylene/multiwall carbon nanotube (HDPE/MWCNT) composite films was measured by laser pulse method. It is found that the TC increased quickly with the increase of MWCNT fraction when the volume fraction of MWCNT was below 3.35%. However, as the volume fraction of MWCNT was over 3.35%, the increasing rate became slow. A new percolation model was proposed based on the effect of MWCNT network to simulate the TC of HDPE/MWCNT composite films. The simulation result was in good agreement the experimental data well. In addition, the relationship of TC with the increase of temperature was also discussed. Supported by the National Natural Science Foundation of China (Grant No. 90606008 and 50706057)     

取样对激光法测定导热系数的影响

以建筑陶瓷、石墨砖和Si3N4-SiC砖为主要试样,研究取样数量、取样位置及其方向对激光法测定材料导热系数结果的影响。结果表明,对于均质材料,随着取样数量的增加,导热系数的测定结果趋于其真值,结合目前设备的技术条件,认为取2～3个样品进行测试即可获得较理想的结果;而对于非均质材料,取样位置和方向都对其导热系数的测定结果有很大的影响,这主要是由于非均质材料的结构或组成随着取样位置和方向的不同而造成的,非均质材料的取样数量至少为5个。     

不同热交换条件下阴燃温度场变化规律研究

通过搭建小尺寸实验平台,选取不同长度和厚度的材料,改变与外界的换热条件,探讨聚氨酯泡沫材料在阴燃及向明火转化过程中温度场的变化规律.结果表明:在不同热交换条件下,阴燃区域温度场变化很大,温度增加幅度达到150℃.增加聚氨酯泡沫材料的长度和厚度,阴燃区域温度升高速度加快,容易达到气相反应所需的温度,并转为明火燃烧.聚氨酯泡沫材料在改变长度和厚度后以15℃冷水、80℃热水和空气作为换热条件时,对外的散热量分别为:2001.37,1010.8,108.28,1779.28,898.66,95.87,1601.62,809.16,87.15 kJ.     

环氧树脂改性聚氨酯羟基组分的合成及应用

为提高发泡聚氨酯材料的界面粘接性能,利用二乙醇胺与环氧树脂反应合成端羟基环氧树脂,再将其涂敷于发泡模具的内表面,加入聚氨酯羟基组分并与稍过量的异氰酸酯组分混合均匀后发泡成型,制得环氧树脂改性聚氨酯泡沫材料.研究了合成反应的温度、时间、配比以及反应动力学方程.红外光谱分析结果显示产物的环氧基特征吸收峰消失,且羟基特征吸收峰增强变宽,说明环氧基参与了反应并生成了端羟基环氧树脂.性能测试实验的结果表明:环氧树脂改性聚氨酯具有凝胶、固化快等特点,环氧树脂链段的引入可以将聚氨酯发泡材料的界面粘接强度提高约57％.     

推算CFCs替代物导热系数的新的基团贡献法

在Ｒｏｙ和Ｔｈｏｄｏｓ法的基础上，得到了一种适合于低压下甲烷系和乙烷系氟里昂气体导热系数的推算方法。用１７种氟里昂在Ｔ＝２５０～５００Ｋ范围内，对新方法作了验算。计算表明，新方法的计算精度比原方法有明显提高。     

焙烧炭砖孔结构和导热系数与硅粒度变化关系

借助于X射线衍射仪、压汞仪、激光导热仪、扫描电子显微镜和能谱分析仪等测试手段,研究了分别含3种不同粒度硅粉（中位径分别为2．3、45．0、115．6μm）焙烧炭砖试样中的孔结构和导热系数的变化。结果表明,含硅粉的炭砖试样经焙烧后内部均生成pSiC、Si2N2O和石英等相,粒度过粗,试样内有单质硅残留;随着硅粉粒度的减小,生成碳化硅晶须的长径比变小。对所选用的3种粒度硅粉,随着硅粉粒度的减小,焙烧后炭砖试样的孔径分布范围逐渐变窄,小于1μm气孔孔容积变大,而平均孔径变小。受炭砖试样组成和孔结构影响,硅粉粒度变小,导热系数下降。细小气孔容积与导热系数呈反比关系,即细小气孔增多,导热系数下降。     

Theoretical and experimental study of the thermal conductivity of nanoporous media

The nanoparticle thermal conductivity and nanoscale thermal contact resistance were investigated by molecular dynamics(MD) simulations to further understand nanoscale porous media thermal conductivity.Macroscale porous media thermal conductivity models were then revised for nanoporous media.The effective thermal conductivities of two packed beds with nanoscale nickel particles and a packed bed with microscale nickel particles were then measured using the Hot Disk.The measured results show that the nano/microscale porous media thermal conductivities were much less than the thermal conductivities of the solid particles.Comparison of the measured and calculated results shows that the revised combined parallel-series model and the revised Hsu-Cheng model can accurately predict the effective thermal conductivities of micro-and nanoparticle packed beds.     

Analysis and calculation of thermal conductivity of rock in deep strata

The thermal conductivity of rock is an important parameter for the deep mine and the geothermal development. It is often not possible to measure the thermal conductivity of the rocks present in the deep strata, and the usual approach is to calculate thermal conductivity including mineralogy and porosity. The compositions of core samples from the MID01 borehole in the Bj?rk? area were determined, and the minera composition was classified. The calculation of the thermal conductivity of rock in the borehole was carried out, and the main factors for the thermal conductivity of rock were analyzed. The results show that the calculated thermal conductivity of rock is reliable and useful for the design and calculation of geothermal development in the Bj?rk? area. Foundation item: Project(50490274) supported by the National Natural Science Foundation of China; project supported by the Postdoctoral Science Foundation of China and Bj?rk? project supported by the Energy Agency of Sweden     

Analysis and calculation of thermal conductivity of rock in deep strata

The thermal conductivity of rock is an important parameter for the deep mine and the geothermal development. It is often not possible to measure the thermal conductivity of the rocks present in the deep strata, and the usual approach is to calculate thermal conductivity including mineralogy and porosity. The compositions of core samples from the MID01 borehole in the Bjorko area were determined, and the mineral composition was classified. The calculation of the thermal conductivity of rock in the borehole was carried out, and the main factors for the thermal conductivity of rock were analyzed. The results show that the calculated thermal conductivity of rock is reliable and useful for the design and calculation of geothermal development in the Bjorko area.