关键词: 多相流, 介尺度, 曳力, 群体平衡模型, 计算流体力学

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