丝状柔性颗粒动力学特性及其气固流化行为研究

Flexible filamentous particle is one typical kind of non-spherical particle, study on their dynamic behavior is appraised as the difficult problem in the frontier of particle research in the world. According to our former researches on the spherical particles and the slender ones, the systemic study on the dynamic characteristics for flexible filamentous particles and their fluidization behavior under heterogeneous gas-solid two-phase flow was put forward. The method for constructing flexible filamentous particles with rootless multi-rigid body system was established. Based on the slender-body theory and the theory of multi-rigid-body dynamics, the dynamic model of flexible filamentous particles in a heterogeneous flow field was established especially with the consideration of inner coupling induction. The drag models respectively for multi-dispersive each flexible filamentous particle and their particle swarm were corrected. The dynamic characteristics for flexible filamentous particles and the fluidization behavior under heterogeneous gas-solid two-phase flow were studied. With the combination of visual simulations and experiments, the established model could be validated and perfected, and the distribution characteristics for bulk particles and the multi-factor influence, as well as the particle cluster were disclosed under operating conditions. The former relative research has gained important results, and the further study as well as the research results of this program could provide a theoretical foundation for these particles, which could be useful for perfecting the theoretical system of numerical simulation on non-spherical particles.

丝状柔性颗粒是类极具代表性的非球形颗粒，对其运动特性的研究是目前颗粒研究领域的前沿和难题。基于前期对球形颗粒和细长杆状颗粒的大量研究，本项目提出开展丝状柔性颗粒的动力学特性及其在非均匀气固体系下流化行为的系统研究：建立基于无根多刚体系统构建丝状柔性颗粒的方法；建立基于细长体理论和多刚体动力学理论的丝状柔性颗粒在非均匀流场中的动力学模型，尤其考虑颗粒内部耦合效应；修正多分散的丝状柔性单颗粒及其颗粒群的曳力模型；研究非均匀气固体系下丝状柔性颗粒的运动特性和流化行为；将可视化模拟与实验研究相结合，验证并完善数值模型，揭示运行工况下较大量丝状柔性颗粒的分布特性、多因素的影响规律及颗粒絮团机理。前期的研究已取得重要成果，本项目的深入研究及其成果可为该类颗粒的研究奠定理论基础，有助于完善非球形颗粒的数值研究理论体系。

丝状柔性颗粒是类具有代表性的非球形颗粒，在纺织、农业、化工、能源、环保和医药等领域都有着十分广泛的应用，对丝状柔性颗粒的气固流化研究是多个领域中的共性科学问题之一。本项目开展了丝状柔性颗粒的动力学特性及其在非均匀气固体系下流化行为的相关研究：（1）丝状柔性颗粒的构建：将每一个丝状柔性颗粒视为细长片状，沿其长度方向均匀离散成颗粒段，颗粒段通过铰约束连接成细长体链，可视为一个无根多刚体系统，构建了基于无根多刚体系统结构的丝状柔性颗粒。（2）丝状柔性颗粒动力学模型：首先，对于每个颗粒段计算其相关动力学参数；其次，相邻颗粒段之间通过铰约束连接，由约束方程求解；然后，结合第一类拉格朗日方程，得多刚体系统的动力学方程；最后，经初步计算与实验确定颗粒合适的离散度和相关计算参数。（3）曳力模型及曳力修正：基于欧拉-欧拉方法，研究了气固体系下的颗粒的曳力模型：Gidaspow模型、Schiller模型、Syamlal-OBrien模型和Wen-Yu模型以及修正的Syamlal-OBrien模型；分析了不同工况下的颗粒相轴径向分布规律；基于曳力修正系数及修正的Syamlal-OBrien模型，分别研究了球形颗粒、椭圆颗粒及片丝状颗粒的流化过程，分析了不同工况下的颗粒相轴径向分布规律：在提升管内，球形颗粒的浓度分布相对均匀，非球形颗粒的浓度分布不均匀，且随着非球形度的增加，颗粒相浓度分布的不均匀程度也增加。（4）非均匀气固体系下丝状柔性颗粒的流化行为：基于所建立的丝状柔性颗粒的运动模型，对具有一定长度分布的丝状柔性颗粒在非均匀气相场中的流化运动展开了一系列模拟研究，着重分析了颗粒在流化床提升管内的数量浓度分布特性；同时，在现有的冷态流化床实验台上，以烟丝这类细长柔性丝状颗粒为研究对象进行流化研究，获得了的烟丝颗粒在提升管内的分布与浓度的实验结果，验证了所建立模型；探讨了入口风速和加料速率对颗粒浓度分布的影响，获得了流化过程中颗粒的分布以及流化参数影响颗粒分布特性的规律性结论。实现了对丝状柔性颗粒流动特性的可视化研究，可揭示流化床内颗粒复杂的运动、分布规律及颗粒絮团机理。