空心材料导热性能预测研究

本文建立了一种预测空心材料导热性的方法。研究了空心材料的导热性。用柱形空心材料分析了体分比和孔洞的排列方式对整体材料导热性的影响，用圆柱形、方柱形空心材料和含裂纹材料，分析了空心形状对材料导热性的影响。同他人的实验结果和某些现有的理论模型比较表明，本文方法是有效的。本文的结果能够很好地解释实验结果。     

Effective Thermal Conductivity of Liquid-Saturated Coatings and Their Liquid Vaporisation Behaviour

The effective thermal conductivity is an important element in understanding the thermal response to heating of a paper coating, e.g. during drying in heatset web-offset, and thus it not only affects the drying efficiency but also affects print quality detriments like web fluting. This study examines both the effective thermal conductivity of liquid-saturated ground calcium carbonate coating structures as well as the vaporisation behaviour from these structures. The liquids used for saturation were mineral oil and water in order to resemble ink and fountain solution, respectively, both of which are present in the traditional heatset web-offset process. The effective thermal conductivities of liquid-saturated coating structures are discussed in regard to the corresponding unsaturated systems by using a Lumped Parameter Model. It is shown that the liquid saturation has a dominant effect in determining the effective thermal conductivity. Since this effect is not fully captured by the model, other mechanisms like an apparent pigment–pigment connectivity increase by liquid bridging and the role of liquid in changing the contact resistance during the measurement of thermal conductivity are discussed. In addition, the transformation of three-dimensional structures to an equivalent two-dimensional modelling is evaluated. The vaporisation behaviour of mineral oil and water is studied by a thermogravimetric analysis. By following the changes in maximum evaporation temperatures and evaporation rates, the addition of binder is seen to lead to a reduction in the vaporisation rate of both liquids. Since there is little to no interaction between the liquids and the binder, the confinement caused by the geometry change induced by binder addition is identified as the mechanism resulting in elevated vapour pressure within the structure.     

A two-scale method for identifying mechanical parameters of composite materials with periodic configuration

In this paper, a two-scale method (TSM) is presented for identifying the mechanics parameters such as stiffness and strength of composite materials with small periodic configuration. Firstly, a formulation is briefly given for two-scale analysis (TSA) of the composite materials. And then a two-scale computation formulation of strains and stresses is developed by displacement solution with orthotropic material coefficients for three kinds of such composites structures, i.e., the tension column with a square cross section, the bending cantilever with a rectangular cross section and the torsion column with a circle cross section. The strength formulas for the three kinds of structures are derived and the TSM procedure is discussed. Finally the numerical results of stiffness and strength are presented and compared with experimental data. It shows that the TSM method in this paper is feasible and valid for predicting both the stiffness and the strength of the composite materials with periodic configuration.The project supported by the Special Funds for Major State Basic Research Project (2005CB321704) and the National Natural Science Foundation of China (10590353 and 90405016). The English text was polished by Yunming Chen.     

Thermomechanical response of metallic sandwich tubes with prismatic cores considering active cooling

In this paper, the transient temperature distribution and the thermomechanical response of sandwich tubes with prismatic cores are analyzed considering active cooling. The effective thermal conductivities of prismatic cores with active cooling are derived. By using the effective thermal conductivities, the transient temperature fields of the tubes are predicted and are found to be very close to the results of finite element simulations, which confirms the correctness of the effective thermal conductivity. Based on the high-order sandwich shell theory, the thermal structural responses of sandwich structures are studied and compared with the results of finite element simulations. The reduction of the thermal structural responses as a result of active cooling is studied to demonstrate the advantages of prismatic cellular materials. The design of replacing the solid metal with cellular materials which has the capability of active cooling can reduce the temperature and the thermal structural response of the structure.     

Multi-scale FE computation for the structures of composite materials with small periodic configuration under condition of coupled thermoelasticity

In this paper, the multi-scale computational method for a structure of composite materials with a small periodic configuration under the coupled thermoelasticity condition is presented. The two-scale asymptotic (TSA) expression of the displacement and the increment of temperature for composite materials with a small periodic configuration under the condition of thermoelasticity are briefly shown at first, then the multi-scale finite element algorithms based on TSA are discussed. Finally the numerical results evaluated by the multi-scale computational method are shown. It demonstrates that the basic configuration and the increment of temperature strongly influence the local strains and local stresses inside a basic cell. The project supported by the National Natural Science Foundation of China (19932030) and Special Funds for Major State Basic Research Projects     

Determination of specific heat and true thermal conductivity of glass from dynamic temperature data

A method to determine the true specific heat and true thermal conductivity for glass and other semitransparent materials from dynamic temperature data is presented. A unique fabrication technique to obtain high quality dynamic temperature data from glass test plates employing thermocouples fused to the glass is described. The true thermal conductivity and specific heat of float glass has been measured using these techniques, and the results are compared with the scant data available in the literature. Sensitivity of the measured specific heat and thermal conductivity to sources of uncertainty is identified and these are discussed.     

Effective thermal conductivity of dispersed materials

Measurements have been made by the comparison method for the effective thermal conductivity of dispersed materials which consist of substances with different thermal conductivities. The applicability of existing predicting formulae is discussed in detail as comparing their predicted values with the present data. A new predicting formula is proposed through analyzing the experimental data, the numerical results, and also the data obtained with the electrolytic-bath. It is found that the proposed formula has a wider range of applicability than that of previously reported ones.     

Topological design of structures and composite materials with multiobjectives

This paper studies the influence of heat conduction in both structural and material designs in two dimensions. The former attempts to find the optimal structures with the maximum stiffness and minimum resistance to heat dissipation and the latter to tailor composite materials with effective thermal conductivity and bulk modulus attaining their upper limits like Hashin–Shtrikman and Lurie–Cherkaev bounds. In the part of structural topology optimization of this paper solid material and void are considered respectively. While in the part of material design, two-phase ill-ordered base materials (i.e. one has a higher Young’s modulus, but lower thermal conductivity while another has a lower Young’s modulus but higher conductivity) are assumed in order to observe competition in the phase distribution defined by stiffness and conduction. The effective properties are derived from the homogenization method with periodic boundary conditions within a representative element (base cell). All the issues are transformed to the minimization problems subject to volume and symmetry constraints mathematically and solved by the method of moving asymptote (MMA), which is guided by the sensitivities with respect to the design variables. To regularize the problem the SIMP model is explored with the nonlinear diffusion techniques to create edge-preserving and checkerboard-free results. The illustrative examples show how to generate Pareto fronts by means of linear weighting functions, which provide an in-depth understanding how these objectives compete in the topologies.     

含空心纤维热电复合材料的能量转换效率及力学性能

空心纤维常用于热电复合材料的结构设计。纤维附近产生的不均匀温度场会引起局部热应力集中,威胁材料的可靠性并可能导致结构失效。本文采用圆环夹杂模型,研究了含空心纤维热电复合材料在均匀远场电流和能流作用下的力学响应。基于非线性全耦合的热电本构方程,利用复变函数中的级数法得到了纤维和基体中热电场和应力场的解析解。通过数值算例,分析了空心纤维的传导能力和几何尺寸对温度场、应力场和局部热电转换效率的影响。结果表明：随着空心纤维内径和界面热阻的增大,界面周围的应力场增大,但并不改变应力场的分布趋势。此外,我们发现：温度分布和应力场对几何参数比对界面热阻更为敏感。     

Thermal energy storage： Challenges and the role of particle technology

Thermal energy is at the heart of the whole energy chain providing a main linkage between the primary and secondary energy sources. Thermal energy storage （TES） has a pivotal role to play in the energy chain and hence in future low carbon economy. However, a competitive TES technology requires a number of scientific and technological challenges to be addressed including TES materials, TES components and devices, and integration of TES devices with energy networks and associated dynamic optimization. This paper provides a perspective of TES technology with a focus on TES materials challenges using molten salts based phase change materials for medium and high temperature applications. Two key challenges for the molten salt based TES materials are chemical incompatibility and low thermal conductivity. The use of composite materials provides an avenue to meeting the challenges. Such composite materials consist of a phase change material, a structural supporting material, and a thermal conductivity enhancement material. The properties of the supporting material could determine the dispersion of the thermal con- ductivity enhancement material in the salt. A right combination of the salt, the structural supporting material, and the thermal conductivity enhancement material could give a hierarchical structure that is able to encapsulate the molten salt and give a substantial enhancement in the thermal conductivity. Understanding of the structure-property relationships for the composite is essential for the formulation design and fabrication of the composite materials. Linking materials properties to the system level performance is recommended as a key future direction of research.