纳米纤维传热传质特性的细观机理研究

Disease, energy shortage and environment pollution have seriously threatened human survival and development. It is an effective way to mitigate above problems using the nanofibers technology. There is not a systematic theory and method which can explain exactly and quantificationally heat and mass transfer of nanofibers such as seepage flow, diffusion and heat transfer until now. So the micro-mechanisms of heat and mass transfer in nanofibers is not clear. The pore structure for most of nanofibers is excessively intricate in practical applications. The geometrical structure of nanofibers is disorderly and unsystematic, which makes it difficult to describe heat and mass transfer of nanofibers accurately and completely. The microstructure of nanofibers such as the pore size distribution satisfies the fractal scaling law, which has been verified. In this project, considering the effects of Knudsen of gas and capillary of liquid on transport properties of nanofibers, the geometrical structure parameters of nanofibers will be combined with heat and mass transfer of nanofibers by analyzing properly and synthetically. Heat and mass transfer properties of nanofibers such as permeability, diffusivity coefficient and thermal conductivity will be studied based on fractal theory, numerical simulations and experiment. And the actual structure parameters of nanofibers will be optimized using genetic algorithm and experiment. Then the fractal analytical expressions of quantitative calculation for heat and mass transfer of nanofibers will be derived. A more complete theory and method of heat and mass transfer will be proposed and developed in nanofibers by the research of this project. Besides, the aims of this project is to provide the theoretical basis for developing functional clothing and designing highly efficient filter system, and so on.

疾病、能源短缺和环境污染严重威胁着人类的生存和发展，应用纳米纤维技术是缓解该问题的有效途径之一。目前还没有系统的理论和方法能够准确地定量解释纳米纤维的传热传质如渗流、扩散和传热，其传热传质细观机理尚不明确。大部分实际应用的纳米纤维的孔隙结构异常复杂，这种杂乱无章的几何结构使得难以对其传热传质进行准确和完整的数学描述。纳米纤维的微结构如孔隙大小分布已被证明满足分形标度律，本项目拟通过恰当的综合分析把纳米纤维的几何结构参量和其传热传质有机地组合起来，并考虑气体的努森效应、液体毛细管效应对其输运性能的影响，采用分形理论、数值模拟和实验来研究纳米纤维的传热传质特性如渗透率、扩散系数和热导率，然后应用遗传算法结合实验来优化纳米纤维的实际结构参数，得到其定量计算的分形解析解。通过本项目的研究，有望提出和建立一套较完整的纳米纤维传热传质理论和方法，并为功能性衣服的开发和高效过滤系统的设计等提供理论依据。

随着人口的增长和工业的发展，人类疾病、资源匮乏和能源短缺逐渐威胁着我们的生存与发展，应用纳米纤维技术是缓解该问题的有效途径之一。本项目主要研究内容为：（1）纳米纤维渗透率的研究；（2）纳米纤维中气体扩散系数的研究；（3）纳米纤维热导率的研究；（4）纳米纤维几何结构参数的优化。重要结果和关键数据如下：（1）毛细压力随着饱和度和孔隙率的增加而减小、随着纤维体积分数和迂曲度分形维数的增加而增加。（2）液相相对渗透率随着饱和度的增加而增加，气相相对渗透率随着饱和度的增加而减小。（3）含颗粒的纤维多孔介质的绝对渗透率随着颗粒直径和纤维直径的增加而增加，Kozeny-Carman 常数随着迂曲度分形维数的增加而增加，无量纲渗透率随着迂曲度分形维数的增加而减少。（4）具有粗糙表面的纤维的Kozeny-Carman 常数随着粗糙度、迂曲度分形维数、孔隙率、微孔面积分形维数的增加而增加，具有粗糙表面的纤维的无量纲渗透率随着粗糙度和迂曲度分形维数的增加而减少。（5）气体有效扩散系数随着孔隙率和微孔面积分形维数的增加而增加、气体有效扩散系数随着迂曲度分形维数的增加而减小。（6）有效热导率随着粗糙度和迂曲度分形维数的增加而减少。（7）无量纲渗透率与无量纲有效扩散系数的比值随着孔隙率和迂曲度分形维数的减小而减小，该结果表明，低孔隙率和低迂曲度分形维数对防风或者防水的纳米纤维织物是有利的。无量纲有效热导率与无量纲有效扩散系数的比值随着迂曲度分形维数的增加而增加，该结果表明低迂曲度分形维数对热防护服纳米纤维织物是有利的。优化结果表明，较规则排列的纳米纤维织物对防护服（如防风或者防水的纳米纤维织物和热防护服纳米纤维织物）是有利的，因为低迂曲度分形维数暗示着纤维在纳米纤维中更规则的排列。. 通过本项目的研究，提出和建立了一套较完整的纳米纤维传热传质理论和方法，可为功能性衣服的开发和高效过滤系统的设计等提供理论依据。