Abstract Gas-solid fluidization technology has been commercialized in many industrial applications since its implementation in the fluid catalytic cracking process in the early 1940s, however, the understanding of the complex hydrodynamics of gas-solid flow inside fluidized beds is still far from satisfactory due to its dynamic and multiscale nature, especially, the critical role played by mesoscale structures. In recent decades, computational fluid dynamics (CFD) has become an important toolkit in understanding the physics of complex gas-solid flow and then for the scale-up, optimization and design of gas-solid fluidized bed reactors. This article presented a pedagogical and comprehensive review to the Navier-Stokes order continuum theory for CFD simulation of the hydrodynamics of gas-solid fluidization, without taking the effects of heat and mass transfer as well as chemical reactions into consideration. A concise introduction to the methods for multiscale CFD simulation of gas-solid fluidization was firstly provided, which include direct numerical simulation, (coarse-grained) discrete particle method, kinetic method, continuum method and mesoscale-structure-based multiscale method. The underlying postulates of homogeneous continuum theory that assume the structure inside each computational cell is (nearly) homogeneous were then examined, followed by an overview of the constitutive relationships available in literature, including the particle phase stress models, the interphase drag models and the models for particle-wall interactions. The importance of mesoscale structures that take the form of gas bubbles and/or particle clusters and streamers in the quantification of the hydrodynamics of gas-solid flows was then addressed, and the explicit resolution (or highly resolved) method and implicit modeling method for quantifying the effects of mesoscale structures in continuum modeling of gas-solid fluidization were highlighted. Coarse grid simulation of large scale fluidized beds with proper mesoscale, sub-grid scale or turbulent models for constitutive relationships were then reviewed, focusing on the filtered method, turbulence modelling and heterogeneity-based method where the energy-minimization multi-scale (EMMS) based method is a representative. Finally, the scope for the further research areas is described.

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致密气固流的连续介质理论：最新评论

摘要 气固流化技术自 1940 年代初在流化床催化裂化过程中实施以来，已在许多工业应用中实现商业化，然而，由于流化床内气固流的复杂流体动力学，人们对它的理解仍然不尽如人意。它的动态和多尺度性质，尤其是中尺度结构所发挥的关键作用。近几十年来，计算流体动力学 (CFD) 已成为理解复杂气固流物理以及气固流化床反应器的放大、优化和设计的重要工具包。本文对用于气固流化流体力学 CFD 模拟的 Navier-Stokes 顺序连续体理论进行了教学性和全面的回顾，没有考虑传热传质和化学反应的影响。首先简要介绍了气固流化多尺度CFD模拟方法，包括直接数值模拟、（粗粒）离散粒子法、动力学法、连续介质法和基于中尺度结构的多尺度方法。然后检查了均匀连续体理论的基本假设，即假设每个计算单元内的结构（几乎）是均匀的，然后概述了文献中可用的本构关系，包括粒子相应力模型、相间阻力模型和模型用于粒子-壁相互作用。然后讨论了以气泡和/或粒子簇和流注形式出现的中尺度结构在气固流流体动力学量化中的重要性，并讨论了用于量化的显式分辨率（或高分辨率）方法和隐式建模方法强调了中尺度结构在气固流化连续介质模型中的影响。然后回顾了具有适当中尺度、亚网格尺度或本构关系的湍流模型的大型流化床的粗网格模拟，重点是过滤方法、湍流建模和基于异质性的方法，其中能量最小化多尺度 (EMMS)基于方法是一个代表。最后，描述了进一步研究领域的范围。