Abstract: Bubbling fluidized beds have been widely used in industrial applications because of its good mass and heat transfer behavior, where the heterogeneous structures such as bubbles are widely present, and these complex structures significantly affect the mass, momentum, and heat transfer as well as chemical reactions in the fluidized bed. The continuum model is selected to simulate the industrial fluidized beds by considering both of the computer cost and efficiency. In order to improve the accurate prediction of the continuum method simulation, it's very important to quantify reasonably the relationship between heterogeneous structures and three transfers/chemical reactions. The structure two-fluid model has been proposed as a novel continuum model, which has taken into account the influence of the heterogeneous structures such as particle clusters in the governing equations and the constitutive relations, therefore, this method is a complete and logically self-consistent in terms of heterogeneous structures. In this study, the structural two-fluid model is extended to the numerical simulation of bubbling fluidized bed: in the deducing the governing equations, the heterogeneous gas-solid system is divided as the particle-dominated emulsion phase and gas-dominated bubble phase, which are defined as two continuous fluids and permeate each other; for closing the constitutive relations, the involved bubble diameter, solid fraction in the emulsion phase and its viscosity have considered the influence of heterogeneous structures such as bubbles by some empirical correlations. As shown in the simulated results, the structural two-fluid model can successfully predict the hydrodynamics characteristics of gas-solid flow in the bubbling beds, thus validating the applicability of the structural two-fluid model in the simulation of bubbling fluidized beds. Moreover, the bubble size as an essential factor has an impact on the interaction between bubble phase and emulsion phase, which leading to the different simulation results with different bubble size correlations.

Key words: multiphase flow, bubbling fluidized bed, Mesoscale structure, bubble, continuum model

摘要： 气固鼓泡流化床因具有较好的传热传质特性已被广泛应用于工业生产，而气泡这类非均匀结构普遍存在于流化床中，它显著影响流化床内动量、能量和质量传递以及化学反应过程。合理描述非均匀结构与三传一反的定量关系对提高连续介质模型模拟的准确性至关重要。结构双流体模型在控制方程及本构关系方面均考虑气固系统内非均匀特性的影响，是一种逻辑自洽、完备地考虑了介尺度结构的全新连续介质模型；本研究拓展了结构双流体模型应用于鼓泡流化床的数值模拟，在构造控制方程时将系统划分成颗粒主导的乳化相和气体主导的气泡相这两类相互渗透的连续流体，同时构造本构关系时涉及的气泡直径、乳化相固含率及黏度等均考虑非均匀结构影响。模拟结果表明，结构双流体模型可成功预测鼓泡床系统内的气固流动特性，同时确定气泡直径影响稀/密相相间相互作用，对模拟结果影响显著。

关键词: 多相流, 鼓泡流化床, 介尺度结构, 气泡, 连续介质模型