纤丝状湿颗粒群在高温气流中的热、质传递机理及调控机制研究

Filamentous particle is a typical kind of non-spherical particle, and has been extensively found in many operations in energy, environment and chemical industries. These flexible particles have some special structural characteristics, such as slim, long and flexible, which result in the complexity of the gas-solid flows system. However, there is still lack of research on the information and details of the flow, heat and mass transfer between filamentous particles and gas phase. To solve these problems, this project focuses on the heat and mass transfer characteristics of filamentous particles in the higher-temperature gas phase. A 3-D physical model on filamentous particles is proposed based on the rod-hinge model. The contact heat and mass transfer models of the gas-solid flows are developed. The heat and mass transfer behavior of filamentous particles are tracked by CFD-DEM method. The important thermodynamic parameters of the gas-solid flows system are obtained by experimental methods. Moreover, the experimental data is used to further improve the precision and reliability of the heat and mass transfer model on filamentous particles. The influence of particle structure, gas parameters and boundary conditions on the heat and mass transfer processes is discussed. To further understanding the internal logic and mechanism between kinetic behaviors and characteristics of heat and mass transfer, the structure of particles and flow patterns are taken into account. The aim of this project is to obtain the evolution rule of thermodynamic and drying characteristics, and transport mechanism of filamentous particles in the high-temperature gas flow. The research would supply theoretical basis for studying on gas-solid flow and developing method on non-spherical particles.

纤丝状颗粒是一类典型的非球形颗粒，广泛存在于能源、环保、化工等领域。细长、柔软且易变形的形状特征导致颗粒间相互作用极其复杂，而有关纤丝状颗粒流动与传热传质的研究目前很不成熟，相关理论和规律的认识十分匮乏。基于此，本项目提出通过建立一种三维“连杆-铰链”组合新模型，构建颗粒间碰撞传热传质数理模型；基于CFD-DEM方法，跟踪每一个纤丝状湿颗粒在高温流场中的热量传递和水分迁移情况；结合静态和动态实验获得气固两相在堆积和流化状态下的热力学参数，验证上述建模方法的合理性和可行性；重点考察颗粒形状、气相参数和边界条件对气固流动系统内热质交换过程的影响，探究颗粒结构-气固流动形态协同作用纤丝状湿颗粒群热质传递机理。旨在系统地掌握纤丝状湿颗粒群动力学行为对其热质交换特性的影响规律，阐明纤丝状湿颗粒在高温气流中的热质传递机理，获得强化纤丝状湿颗粒传热传质的调控手段，发展具有创新性的非球形颗粒研究方法。

复杂气固两相流系统在自然界和工业应用中广泛存在，而以纤丝形状为代表的非球形颗粒常见于新能源燃料、食品、化工、复合材料等领域。本项目针对纤丝状生物质颗粒在高温气流中的热、质传递机理及调控机制开展了研究。提出了一种描述纤丝状颗粒形变卷曲过程的“多球-铰链”模型，采用CFD-DEM气固两相耦合方法，构建了纤丝状湿颗粒群在复杂气固系统中的接触碰撞与流动数理模型，结合提升管输运系统实验，验证了该模型的可行性和适用性，形成了此类非球形颗粒群在气相场中流动过程的计算模型。基于上述模型和数值方法探究了表观气速、颗粒质量流量、颗粒密度、颗粒长度、气料比等参数对纤丝状湿颗粒群在提升管内动力学行为的作用机理，分析并研究了纤丝状湿颗粒群在输运过程中的聚团现象及其发生机制。研究结果表明：纤丝状湿颗粒群在输运过程中容易在近壁面区出现聚团、颗粒间相互缠绕加剧，通过加强气流对颗粒相的扰动，有助于提升颗粒分布均匀性。针对旋转滚筒干燥器内典型的气固两相间动、热、质耦合传递过程，本项目采用实验方法优化了Friedman-Marshall模型，获得了表征大量纤丝状颗粒在滚筒设备内运动特性的数学关联式，建立了非球形颗粒与气流间热-力关系，通过工业级热态滚筒实验结果进一步修正上述数学模型。重点考察了滚筒内抄板结构、倾角、气流速度、气流温度等因素对纤丝状湿颗粒群在流动中传热传质行为的影响，阐明了操作参数-滚筒结构协同作用大量纤丝状湿颗粒运动与热质耦合传递机理，获得了复杂气固两相系统中强化纤丝状湿颗粒群热质传递的调控机制。聚焦国家“双碳”战略，本项目提出的纤丝状颗粒建模方法为新能源高效制备与利用、化石能源洁净低碳化及工业反应器优化设计提供一种新思路。

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