基于分形理论的耦合气固反应热质源的多孔介质热质传递研究

Composite reactive material based on expanded graphite matrix is a typical kind of porous media used in solid-gas reaction system. The heat and mass transfer performances are important index parameters. Due to the complex porous structure and the coupled processes of heat transfer, mass transfer and solid-gas reaction, it was hard to measure the thermal conductivity and gas permeability of the porous media, especially their variations caused by solid-gas reaction. In this project, it was proposed to observe the complex porous structure and establish the model of porous media based on fractal theory, to theoretically investigate the heat and mass transfer performances based on the study of the processes the porous media experienced, i.e. heat transfer process, mass tranfer process and solid-gas reaction, and to experimentally measure the parameters with specially designed test-rigs. The porous media was CT-scanned. The fractal dimensions involved in the model of porous media were determined by observation with SEM and optical microscope, followed by graphic processing and mathematical analysis. The theoretical models of thermal conductivity and gas permeability of porous media in the process of solid-gas reaction were also established. The heat and mass transfer performances were determined from the fractal model of porous media and the simplified equations of heat and mass transfer, as well as the thermodynamics and kinetics of solid-gas reaction. The proceedings of reaction and the variations of heat and mass transfer performances were linked by the change of pore structure, due to solid-gas reaction. Experimental test rigs were specially designed in order to reduce the influence of the proceeding of solid-gas reaction on the measurement of heat and mass transfer performances. The database of thermal conductivity andgas permeability of porous media was established. The experimental data were used to verify and improve the theoretical models. The results of heat and mass transfer performances with solid-gas reaction were ultimately taken to investigate the effect of porous reactive material on the performance improvement of solid-gas reaction system, so as to optimize the parameters in fabrication procedure and structure design. Based on the results of this project, it was possible to better understand the fractal pore structure in porous media, the relationship of the thermal conductivity and gas permeability of the porous media with its pore structure, and the variation of heat and mass tranfer performances in the process of solid-gas reaction. It was also possible to better understand the heat and mass tranfer processes coupled with solid-gas reaction and other similar conditions marked with complex thermal and mass sources. Through the implementation of this project, a practical research method and valuable references were also available to relevent theoretical investigation and experimental testing.

气固反应系统中的膨胀石墨压块基材复合反应材料是一种典型的多孔介质，热质传递性能是其重要的性能参数。由于孔隙结构复杂，传热、传质和反应过程三者相互耦合，较难确定导热系数和气体渗透率，尤其是在反应过程中的变化规律。本项目将利用CT扫描技术，依据分形理论建立孔隙结构模型，通过扫描电镜和光学显微镜多尺度、多维度观察，结合图形处理技术、统计学原理和分形理论，确定孔隙结构参数和分形维数；其次，依据热质传递理论、反应动力学和热力学理论，建立传热、传质和反应模型，结合分形孔隙结构模型，理论分析多孔介质在气固反应过程中的结构改变和热质传递性能的变化；完善现有传热传质性能测试平台，对伴随气固反应过程的多孔介质导热系数和气体渗透率进行实验测量，建立数据库，验证和修正理论模型；最后，分析气固反应系统性能，优化材料的制备工艺和结构参数。通过本项目的实施，还将为相关多孔介质的复杂传热传质问题研究提供有一种可行的方法。

多孔介质具有丰富而复杂的孔隙结构，可广泛用于传热传质强化，如超级电容器、相变储热、热化学反应系统等。制备了多种形态的多孔介质材料。针对多孔介质传热传质过程及其在热利用方面的性能，采用分形理论和火积理论进行了理论研究。本项目部分解决了几个基本问题，主要包括分形维数的确定方法，相变储能过程中的火积优化。提出了基于宏观介质参数和微观参数关联的方法，确定分形维数，避免图像观察过程中的信息缺失对参数确定的影响。针对石墨基材的多孔介质，测试了热物性参数和电学性能参数，初步建立了实验数据库。综合结合火积理论，对传热强化的相变储热结构进行优化，分别针对温度匹配、换热面积匹配和多级设计进行了分析，并得出了相应的优化准则，作出了相关讨论。针对多孔介质在热化学反应过程中的应用，提出了可变温驱动的三效吸附制冷系统原理。在项目实施过程中，已发表论文5篇，参加会议1次，授权专利1项，待申请专利3项，在投论文2篇。项目结果对于分形理论的完善、热利用装置和系统的优化设计有一定的指导价值。