量化稳约双流体模型中稀密相相间质量交换和颗粒聚团结构时空动态演化特性

Accurately mathematical model for gas-solid two-phase flow is critical for the scale-up of fluidized bed reactors via computer simulation. Based on the concept of the compromise of two different dominant mechanisms in competition proposed in mesoscience, an EMMS-based two fluid model (TFM) has been proposed, its rationality and correctness have also been validated preliminarily in the previous works. In this study, we focus on two unsolved key issues in the EMMS-based TFM: (1) qualification of the mass change rate between dilute phase and dense phase and (2) characterization of spatial-temporal evolution of particle clustering structures. Referring to the gas kinetic theory of shock wave, two Boltzmann equations were used to describe the kinetics of particles in dilute phase and in dense phase, respectively. The mass exchange rate between dilute phase and dense phase was then determined from collisional source term of kinetic theory, the key parameter of which was determined by multiscale decomposition. The spatio-temporal evolution of particle clustering structures was described by population balance model (PBM) using internal variables containing size, density and velocity of clusters, the probability of coalescence or breakage in PBM was determined by analyzing the energy dissipation characteristics of the system. With the new constitutive relationships, the simulation precision and application scope of EMMS TFM were expected to be enhanced greatly, thus realizing fast and accurate simulation of industrial scale fluidized beds. It provided strong support to the reasonable design and optimization of fluidized bed reactors.

准确的气固两相流模型是流化床反应器模拟放大的关键所在。根据“介科学”两个控制机制竞争中协调概念建立的稳约双流体模型是一种全新的探索，初步研究已证明稳约双流体模型的合理性和有效性。本项目聚焦稳约双流体模型中两个尚未解决的关键问题：量化稀密相相间质量交换率和颗粒聚团结构时空动态演化特性。借鉴研究激波特性的气体动理论，用两个Boltzmann方程分别描述稀密相颗粒的运动特性，稀密相相间质量交换量通过动理论中的碰撞源项确定，其中的核心待定参数通过多尺度分解的方法确定；颗粒聚团结构时空动态演化特性用以颗粒聚团体积、密度和速度为内变量的群平衡方程描述，其中涉及的颗粒聚团破碎聚并概率通过分析系统能耗确定。通过建立更加合理的本构关系，大幅提高稳约双流体模型的模拟精度和适用范围，实现工业流化床的快速准确模拟，为流化床反应器的合理设计与优化提供支撑。

准确的气固两相流模型是流化床反应器模拟放大的关键所在。根据“介科学”两个控制机制竞争中协调概念建立的稳约双流体模型是一种全新的探索，初步研究已证明稳约双流体模型的合理性和有效性。本项目聚焦统一稳约双流体模型的统计力学基础、完善本构关系：根据EMMS原理中不同控制机制间竞争中协调及尺度划分概念，将非均匀气固系统划分成稀相气体、稀相颗粒、密相气体、密相颗粒四个均匀的子系统，由此四流体依次构造玻尔兹曼方程，由动理论导出四流体对应的宏观流动控制方程及本构关系，随后两两进行组合即可确定两类稳约双流体模型（EFM-I & EFM-II）：其中针对EFM-I，完善包含动力学影响、碰撞作用及拟雷诺效应的气、固相应力；针对EFM-II，通过假设稀密相颗粒/气体分子碰撞导致组份迁移，封闭稀密相相间质量、动量、能量交换。通过建立完整考虑介尺度结构影响的本构关系，大幅提高稳约双流体模型的模拟精度和适用范围，实现工业流化床的快速准确模拟，为流化床反应器的合理设计与优化提供支撑。. 在本项目的支持下以第一作者/第二作者或者通讯作者发表SCI收录论文9篇，其中Chem.Eng.Sci.5篇，Ind.Eng.Chem.Res.1篇，Phys.Fluids 3篇。2022年在首届未来颗粒前沿论坛上做邀请报告。.