加压中高温气固流化床内粘性颗粒的多尺度运动机制研究

Pressurized mid/high temperature gas solid fluidized bed is widely used in energy thermal conversion process, but the hydrodynamic characteristics of cohesive particle under pressurized mid/high temperature circumstance are still unclear. A pressurized quasi-thermal state fluidized bed experimental system will be constructed and experimental particles with controllable cohesive force will be fabricated as well. With the help of various multi-phase flow measurement technologies like X-ray imaging, the effect of operating pressure, particle cohesive force and other critical operating parameters on the particle motion will be investigated. The turbulence-discrete element numerical simulation method for cohesive particle fluidization will also be developed and particles contact model considering cohesive force will be proposed. Based on the method and the model, CFD-DEM simulation of pressurized mid/high temperature gas solid fluidized bed with cohesive particles will be carried out to reveal the multi-scale hydrodynamic characteristics and mechanism of gas solid two phase flow with cohesive particles. The project can be expected to form innovative experimental technology and numerical simulation methods in gas solid two phase flow researching field, as well as promoting the development of design and optimization technique for pressurized mid/high temperature gas solid fluidized bed.

加压中高温气固流化床在能源热转换领域有着广泛的应用前景，目前对加压中高温气固流化床内粘性颗粒的运动规律尚缺乏系统认识。本研究拟构建加压-半热态流化床实验系统，结合专门制备的粘性力可控颗粒，借助和发展X光透视成像等现代多相流测量技术，探究操作压力、颗粒间粘性力等关键参数对床内颗粒流动的影响规律。同时，发展适用于粘性颗粒流态化研究的湍流—离散颗粒元数值模拟方法，构建耦合粘性力作用的核心颗粒接触模型，在此基础上，对加压中高温流化床内粘性颗粒稠密气固流动进行CFD-DEM数值仿真，揭示床内粘性颗粒的多尺度运动机理。本项目有望形成具有创新性的实验和数值模拟方法，丰富气固两相流研究手段，促进加压中高温气固流化床系统设计优化技术的发展。

粘性颗粒的流态化行为较非粘性颗粒要更加复杂，是当前多相流研究领域的热点问题。加压中高温气固流化床在能源热转换领域有着广泛的应用前景，对加压中高温气固流化床内粘性颗粒的运动规律尚缺乏系统认识。本研究从实验和数值模拟研究两个方面，以流化床为研究对象，对粘性颗粒的加压/常压流化特性进行了系统深入的研究。建立了可视化加压流化床实验系统，开展了Geldart-D类粘性颗粒的加压流化实验，研究了操作压力、流化气速、颗粒粒径、颗粒密度、颗粒间粘性力等关键参数对加压流化过程的影响规律。研究获得了粘/湿颗粒加压流化过程的流型特征；揭示了粘/湿颗粒加压流化床层压降、最小流化速度等重要流动特性参数与操作参数之间的变化规律；结合压力脉动信号的时/频域特征分析，发展了粘性颗粒加压流化床内流型特征变化识别方法；结合理论与实验数据分析，获得了D类颗粒加压流化最小流化速度的计算方法。开展了Geldart-C类、D类粘性颗粒群聚团改善的研究，基于微波固体流量测量、压力信号测量、X光透视成像等现代多相流测试技术，获得了引入脉冲风、振动对粘性颗粒流态化运动的影响规律。建立了粘/湿颗粒接触过程捕捉及粘性力实时测量实验平台，利用高速显微成像跟踪粘/湿颗粒对的接触分离过程，精密天平同步测量颗粒间粘性力随分离过程的变化，掌握了颗粒分离过程中粘性力变化规律，与现有湿颗粒间作用力模型进行了对比分析，为微观尺度颗粒间接触粘性力模型建立/选择提供了实验依据。发展了能够用于粘性颗粒流态化仿真的CFD-DEM数理模型，完成了粘性颗粒/非粘性的常压/加压流化过程的三维仿真模拟，揭示了加压、中高温、粘性力对宏观流动结构、介观混合特性、微观颗粒运动的影响规律，实现了微观颗粒间受力与宏观、介观气固流动现象、规律的关联。本研究提高了对粘性颗粒加压流态化行为的认识深度，部分创新性成果促进了非常规气固流的发展。