Abstract:

Mesoscale structures and mechanisms represent one of the critical scientific problems in process engineering such as chemical, metallurgy and energy industries. Although the mathematical model of multiphase flow has made great progress in the past few decades, there are several longstanding problems including the modeling accuracy dependent on adjustable parameters, the limited model applicability, and large computation cost, etc. It is difficult for the model development to adapt to the demand of current rapid development of new technology and new processes. In fact, the multi-fluid model based on the averaging method requires several sub-models to be closed, e.g., interphase forces, coalescence/breakup kernel functions, and turbulence models. These sub-models determine the simulation accuracy of the multi-fluid model. Developing mesoscale models from the perspective of mesoscience provides new avenue through analyzing the dominant mechanisms for the evolution of heterogeneous structures in multiphase flow to improve or reconstruct the closure model. In this paper, two types of mesoscale closed models based on mesoscale stability conditions are summarized: one is used for the momentum transfer between closed phases like mesoscale drag, the other is for the evolution of the characteristic parameters of discrete phases, e.g., the mesoscale population balance model, to calculate the bubble or droplet size distribution. Then, the application of these models in multiphase flow equipment such as fluidized bed, bubble column, airlift loop reactor, stirred tank, rotor-stator emulsification is reviewed, and the future study and key scientific issues are analyzed.

Key words: multiphase flow, mesoscale, drag, population balance model, computational fluid dynamics

摘要：

介尺度结构和介尺度机制是化工、冶金、能源等过程工程中的重要科学问题。尽管多相流数理模型在过去的几十年中已取得长足进展，但仍存在准确性依赖可调参数、模型适用性有限、计算量大等问题，难以适应当前快速发展的新工艺和新过程开发的需求。实际上，基于平均化方法的多流体方程组需要若干子模型封闭，如相间作用力、聚并/破碎核函数以及湍流模型等；这些子模型决定了多流体模型的模拟准确性。从介科学角度发展介尺度物理模型为解决这些问题提供了新的思路。模型可以解析多相流非均匀结构演化的控制机制，进而改进或重构子模型。总结了基于介尺度稳定条件的两类介尺度封闭模型：一类用于封闭相间动量传递，如介尺度曳力；另一类用于封闭离散相特征参数的演化，如介尺度群体平衡模型，计算气泡或液滴尺寸。进而综述了这些模型在流化床、鼓泡塔、气升式环流反应器、搅拌槽、转定子乳化器等多相流设备中的应用，并展望了未来发展方向和关键科学问题。

关键词: 多相流, 介尺度, 曳力, 群体平衡模型, 计算流体力学