【作者】 郑兴华；

【导师】 唐大伟；

【作者基本信息】 中国科学院研究生院（工程热物理研究所） ， 工程热物理， 2012， 博士

【摘要】 本文提出了用于微纳粉体材料传热及蓄热特性的谐波探测方法,测量了微纳热功能粉体材料的有效热导率、热扩散率及吸热系数等参数,分析探讨了密度、尺度、温度及材料种类对样品传/蓄热特性的影响。揭示了相应的传热、蓄热机理,为微纳尺度热功能材料的研发、工艺优化及应用提供了科学理论依据。根据谐波探测技术中热波穿透深度随测量频率的变化关系,分析了探测器长/径比、样品热物性参数等与热波穿透深度的耦合关系。给出了可忽略探测器自身热容及端部热损失对测量结果影响的频率范围。采用标准样品校正,验证了推导的简化一维斜率比较法可用于测量微纳粉体等低热导率材料的有效热导率及热扩散率。利用校准的谐波探测系统测量了不同粒径、温度及密度的纳米siO2粉末样品有效热导率及热扩散率。在忽略气体对流的情况下,计算分析了纳米SiO2粉末样品中固相导热、气相传热及辐射传热的耦合隔热机理。结果表明,在测量范围内,SiO2粉末的有效热导率及热扩散率随温度升高而增大,随颗粒直径增大而减小。受到纳米孔隙对气相传热的抑制,SiO2粉末存在最佳密度,在此密度下,有效热导率最小,热扩散率最大,且最佳密度随颗粒直径的减小而减小。测量了以切片石蜡为芯材、脲醛树脂聚合物为壳材,采用原位聚合法制备的不同壳/芯比、温度、密度的相变微胶囊粉体的有效热导率。结合理论计算分析了样品壳/芯比、密度及温度等对相变微胶囊导热性能的影响规律。给出了用于该类复合材料有效热导率计算的理论模型,确定了当计算误差小于10%时,模型中无量纲数ζ的取值范围为4.8到6,ζ与样品中纵波声速有关,由材料比热、密度、杨氏模量(弹性模量)决定。采用面热源谐波探测技术,测量了相变微胶囊粉体材料的有效吸热系数。结果表明,材料的相变芯材性能及其包覆量是衡量其蓄热能力(包括速度大小与容量大小)的关键。芯材含量越高,其有效吸热系数越大,蓄热能力越强。芯材潜热越大、相变时的有效热导率越大,其有效吸热系数越大,与其周围环境热交换能力越强。更多还原

【Abstract】 The harmonic detection method for characterizing the heat transportation and heat storage performances of micro-and nano-scale powder is proposed in this thesis. The effective thermal conductivity, thermal diffusivity and thermal effusivity of micro-and nano-scale thermal functional powders are measured. The effects of density, size, temperature and materials type on the heat transportation and heat storage performance are discussed. The relevant heat transportation and heat storage mechanism are revealed, which provides scientific theory basis for the development, process optimization and application of micro-and nano-scale thermal functional materials.According to the relationship between the heat penetration depth and the measured frequency in harmonic detection technology, the coupling relation between ratio of length to radius of the sensor and the heat penetration depth and that between the thermophysical properties of the specimen and the heat penetration depth are analyzed. The frequency range in which the heat capacity of the sensor and the heat loss of the sensor ends can be neglected is presented. A simplified one-dimensional (1D) slope comparison method is obtained, which is verified by using the standard specimens. The1D slope comparison method can be used to measure the effective thermal conductivity and thermal diffusivity of lowly thermal-conductive materials, such as micro-and nano-scale powders.The effective thermal conductivity and thermal diffusivity of SiO2powders with different particle sizes and different densities at different temperatures are measured by using the calibrated harmonic detection systems. When the gas convection can be neglected, the coupling insulation mechanisms of the solid conduction, gas conduction and heat radiation for nano-scale SiO2powders are calculated and analyzed. The results show in the measured range, both the effective thermal conductivity and thermal diffusivity of SiO2powders increase with the increasing temperatures, and decrease with the increasing particle size. As the gas conduction is inhibited by the nano-scale pores, there exists an optimum density at which the effective thermal conductivity reaches the minimum; the thermal diffusivity reaches the maximum. The optimum density decreases with the decreasing particle diameter.The effective thermal conductivity of phase change microcapsules with different shell-core rations, temperatures, densities is measured. The phase change microcapsules with paraffin wax as core materials and urea-formaldehyde resin polymers as shell materials are produced by in-situ polymerization process. Based on the theoretical calculations, the influence laws of shell-core rations, density and temperature on the heat conduction performance of phase change microcapsules are analyzed. The theoretical model for the calculation of the effective thermal conductivity of such complex materials is presented. It is believed that when the dimensionless parameter (?)(?) relates to the longitudinal sound velocity in the material and determined by the specific heat, density and Young’s modulus or called elastic modulus) ranges from4.8to6.0, the error is within10%.By using the planar source harmonic detection technology, the effective thermal effusivity of phase change microcapsules is measured. The results show the phase change core materials properties and its covering amount of the materials is the key to evaluate the heat storage capacity of the materials. The effective thermal effusivity increases with the increasing core materials content and so does the heat storage ability. The effective thermal conductivity increases with the increasing latent heat of the core materials during the phase change process, and so does the effective thermal effusivity, which suggests the increasing its heat transfer ability with the surrounding environment.更多还原