Continuum theory for dense gas-solid flow: A state-of-the-art review
Continuum theory for dense gas-solid flow: A state-of-the-art review
复制标题
DOI：
10.1016/j.ces.2019.115428
复制
发表时间：
2020-04
影响因子：
4.7
通讯作者：
Junwu Wang
中科院分区：
文献类型：
--
作者：
Junwu Wang
气固流态化技术自40年代初应用于催化裂化过程以来，已获得了广泛的工业应用，但由于流化床内气固流动的动态性和多尺度性，尤其是中尺度结构的重要性，对流化床内气固流动复杂流体力学的认识还很不完善。近几十年来，计算流体力学（CFD）已成为理解复杂气固流动物理过程，进而用于气固流化床反应器放大、优化和设计的重要工具。本文对Navier-Stokes连续介质理论在不考虑传热传质和化学反应的情况下，用于气固流态化流体力学CFD模拟的研究进行了全面的评述。首先简要介绍了气固流态化多尺度CFD模拟的方法，包括直接数值模拟、（粗粒）离散颗粒法、动力学方法、连续介质法和基于介观结构的多尺度方法。均匀连续介质理论的基本假设，假设每个计算单元内的结构是（近）均匀的，然后检查，随后概述了文献中的本构关系，包括颗粒相应力模型，相间阻力模型和颗粒壁相互作用的模型。阐述了气泡和/或颗粒团簇和流光等中尺度结构在气固流动流体力学定量研究中的重要性，重点介绍了在气固流化连续介质模拟中量化中尺度结构影响的显式分辨率（或高分辨率）方法和隐式模拟方法。然后综述了大尺度流化床的粗网格模拟方法，包括采用合适的中尺度、亚网格尺度或湍流模型来模拟本构关系，重点介绍了滤波方法、湍流模型和基于非均匀性的方法，其中以基于能量最小化多尺度（EMMS）的方法为代表。最后，对进一步的研究领域进行了展望。
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.