中国科学院过程工程研究所机构知识库

气固流态化系统是典型的非平衡系统，呈现出复杂的时空多尺度结构，因而需要使用多尺度方法进行分析。能量最小多尺度(EMMS)模型揭示了介尺度结构及稳定性条件在认识气固流态化系统中的重要作用，在气固流态化系统中得到了广泛应用。本文致力于通过直接数值模拟(DNS)分析流态化不均匀结构，构造气固流态化系统的能耗统计方法，同时对EMMS模型中提出的稳定性条件，即流体悬浮输送单位质量颗粒的能耗Nst趋于最小进行验证。对比基于拟颗粒模型（PPM）的验证工作，本文通过引入加速度并考虑不同颗粒初始分布方式使结论更有说服力，并且基于DNS的研究可以更准确的统计能耗项。本论文各章内容安排如下：第1章 对气固流态化系统进行介绍，并综述了包括实验、经验公式及数值模拟方法在内的研究成果，同时说明三类常用的数值模拟方法：双流体模型(TFM)、颗粒轨道模型以及直接数值模拟的优缺点，阐明了选择直接数值模拟开展本工作的原因。第2章 详细介绍了本论文中采用的直接数值模拟方法，包括流场求解、颗粒运动处理以及流固耦合方式，并通过模拟流体流过静止单颗粒及交错分布的颗粒群验证了数值模拟方法的准确性。第3章 在EMMS模型中悬浮输送流速的统计中考虑加速度的影响，对不同颗粒初始分布方式、不同入口气速的气固流态化体系进行了模拟，得到了悬浮输送流速Ust随时间趋于最小的结论，验证了EMMS模型稳定性条件。第4章 对本论文内容进行总结并对未来的工作进行了展望，目前对EMMS模型稳定性条件的验证仍延续着间接求解的方法，将来随着EMMS模型中的能耗项与气固流态化的能量系统建立更完善的对应关系，通过直接数值方法对EMMS模型中能耗项进行统计将是非常有前景的研究方向。;The gas-solid fluidization system is a typical non-equilibrium system, which presents a complex multi-scale structure of space and time. The energy minimum multi-scale (EMMS) model reveals the important role of mesoscale structures and stability conditions in gas-solid fluidization systems, and it has been widely used in gas-solid fluidization systems.In this paper, direct numerical simulation (DNS) is used to analyze the fluidized heterogeneous structure and to construct the energy consumption statistics method of gas-solid fluidized system. The stability condition proposed by the EMMS model is that the energy consumption Nst for suspending and conveying unit mass particles tends to minimum is proved in this thesis.Compared with validation work using the Pseudo-Particle Modeling (PPM), the acceleration is introduction and differnet initial distributions of particles is considered in this thesis to make the conclusion more persuasive, and the statistics of energy consumption based on DNS is more accurate.The main contents of this thesis are as follows: In chapter 1, gas-solid fluidization system and its non-uniform structure is introduced, and reviews the research results of experiment, empirical formula and numerical simulation method. Illustrates the merit and demerit of three kinds of numerical simulations including two-fluid model, Eulerian-Lagrangian method and direct numerical simulation, in order to explain why we choose direct numerical simulation to study the gas-solid fluidization;In chapter 2, the DNS method used in this paper is introduced in detail, including flow field solution, particle motion treatment and fluid-solid coupling method. The rationality of the DNS method is verified by simulating the fluid through a single particle and fluid through staggered distribution of the particles.In chapter 3, the influence of acceleration is considered in the statistics of suspension and transport velocity in the EMMS model. The gas-solid fluidization systems with different initial particle distribution patterns and different inlet velocity are simulated using DNS. The conclusion that the suspension and transport velocity Ust tends to be minimized with time is obtained, and the stability condition of the EMMS model is verified.In chapter 4, the main results in this thesis is summarized and some future directions on DNS is discussed. The validation of stability conditions of the EMMS model in this thesis still uses the indirect statistical method. In the future, as the energy consumption terms in the EMMS model correspond better with the energy system of gas-solid fluidization, counting the energy consumption terms in the EMMS model directly with DNS would become a very promising research direction.