基于统计相似表征体元颗粒无序堆积流动传热与壁面效应研究

The flow and heat transfer in random packed system of particles is a fundamental process in many fields, such as nuclear and chemical industries. The complexity of the process is mainly caused by the randomness and heterogeneity of the random packed structures, and it is necessary to study the flow and heat transfer by using volume averaged macroscopic method combined with pore-scale microscopic method. However, it is found that, studies on constructions of random packing structures and the definition of the representative elementary volume are still quite insufficient. Meanwhile, the fundamental mechanism and effects caused by the wall effect inside the random packed tube are also unclear. Therefore, in the present project, the statistical similarity principle would be employed to establish a reasonable definition of the random packed representative elementary volume. Furthermore, together with the volume averaged method, the macroscopic hydrodynamic and heat transfer computational model of random packed porous media with wall effect inside should also be improved. In addition, both the electrochemical and macroscopic flow and heat transfer experiments would be carried out to explore the local turbulent fluctuation of the fluid inside different pores of the random packed tubes, and the fundamental mechanism and effects caused by the wall effect inside would be explained. Finally, the regression analysis method based on Genetic Programming and Genetic Algorithm would be used to established the general experimental correlations of macroscopic flow and heat transfer in the random packed tubes with wall effect inside, which would be used to validate and improve the corresponding theoretical models. This result would provide a scientific support for practical engineering applications.

颗粒无序堆积体系内的流动传热过程是核能、化工等众多领域内的基本过程，其复杂性源于孔隙结构的随机性与不均匀性，须将体积平均宏观研究方法与孔隙尺度微观研究方法结合起来研究。但目前在颗粒无序堆积孔隙构建及相应表征体元选取方面还存在较多不足，对于颗粒无序堆积通道内壁面效应的产生机理及其影响机制的研究也相对匮乏。本项目拟依据统计相似原理，确立颗粒无序堆积表征体元的选取准则，结合体积平均方法完善壁面效应下颗粒无序堆积多孔介质内的宏观流动与传热计算模型。开展电化学实验与宏观流动传热性能测试实验，探明颗粒堆积通道不同区域孔隙内流体的局部脉动发展过程，并对壁面效应的产生机理及影响机制进行阐释。在此基础上,运用遗传规划与遗传算法相结合的回归方法建立壁面效应下颗粒无序堆积通道内统一的宏观流动与传热实验关联式，并对理论模型进行验证和完善，从而为实际工程应用提供理论支持。

颗粒堆积体系内的能质传递与转化现象在自然界及实际工业应用中广泛存在，如：地下水污染物扩散、石油/天然气开采、球床反应堆堆芯设计、催化床反应器性能优化、铁矿石烧结与冷却等，了解并掌握颗粒堆积体系内的能质传递与转化规律是保证能源高效利用及相应设备安全运行的前提之一。本项目主要围绕颗粒无序堆积复杂孔隙结构构建、颗粒无序堆积壁面效应影响机制、颗粒无序堆积流态转捩变化规律及颗粒无序堆积有效导热系数快速预测四个方面展开深入研究。在颗粒无序堆积复杂孔隙结构构建方面，基于离散单元法构建了圆球颗粒无序堆积复杂孔隙结构，获得了不同管径粒径比下堆积床内孔隙率的径向变化规律及通道壁面对堆积床孔隙率径向分布的影响机制。在颗粒无序堆积通道壁面效应影响方面，对不同结构圆球颗粒复合无序堆积通道内的流动换热特性进行数值研究，获得了抑制堆积通道壁面效应和提高其综合换热效率的颗粒堆积方法。在颗粒无序堆积流态转捩变化方面，设计并搭建了颗粒无序堆积流动转捩电化学实验平台，基于电化学方法研究了较大管径粒径比条件下不同粒径无序堆积床和不同管径粒径比条件下颗粒无序堆积床孔隙内流体的脉动变化，获得了壁面效应条件下堆积床内流体流态的变化规律。在颗粒堆积有效导热系数快速预测方面，基于欧姆定律和基尔霍夫定律等效热阻网络法，结合统计平均和表征体元方法对颗粒无序颗粒堆积床的有效导热系数进行了合理预测。项目研究结果对颗粒无序堆积复杂孔隙结构构建、表征体元选取、揭示颗粒无序堆积壁面效应对流动转捩及传热影响机制并实现无序堆积床有效导热系数快速准确预测均有重要意义。项目共发表学术论文41篇，其中SCI期刊论文12篇，EI期刊论文9篇，国际会议论文12篇，国内会议论文8篇；受邀国际会议特邀报告1次（PRES2017）；培养毕业博士研究生2名，毕业硕士研究生4名，在读博士研究生4名，在读硕士研究生1名。