基于CFD-DEM耦合的过热蒸汽流化床干燥传热传质机理与模型

During sperheated steam fluidized bed drying, the steam and particle two-phase turbulence flow is coupling with the heat and mass transfer in the drying chamber, such as the steam condensate, the solid particles moisture diffusion and evaporation. The existing mechanism model can not describe above dynamic process, and it can not represent the particle material dynamic properties of actual drying process. This project focuses on the heat and mass transfer mechanism analysis of superheated steam fluidized bed drying process, including the steam condensation heating period, the constant-rate drying period and the falling-rate drying period. The dense particles two-phase turbulent flow coupling with the heat and mass transfer in the drying chamber is described by the CFD-DEM coupling method, and than a realistic mathematical model of superheated steam fluidized bed drying process is extablished and solved numerically. In order to verify and optimize the mathematical model, the fluidized bed drying kinetics experiments by superheated steam and hot air are carried out with the wet ceramic raw particles. Finally, the numerical simulation are conduct with different conditions. The influence of operating pressure, inlet superheated steam temperature and superficial velocity on the drying process, is studied by the numerical simulationt. As a result, a quantitative analysis and process optimization method for superheated steam fluidized bed drying can be represented by the CFD-DEM coupling model, which provides theoretical guidance for the innovation and development of superheated steam fluidized bed drying technology.

针对现有过热蒸汽流化床干燥机理模型不能准确描述干燥室内蒸汽-颗粒两相湍流流动与蒸汽凝结、颗粒湿份扩散与蒸发等传热传质耦合过程，无法表征实际干燥过程中颗粒物料的动态离散特性等问题，本项目基于CFD-DEM耦合方法，重点分析探讨过热蒸汽流化床干燥过程冷凝加热段、恒速干燥段、降速干燥段的传热传质机理，准确描述干燥室稠密颗粒两相湍流与过热蒸汽凝结、颗粒物料湿分扩散与蒸发传热传质耦合过程，构建更切合实际过热蒸汽流化床干燥过程的非定常轴对称二维数学模型,并进行数值求解；搭建实验装置，以陶瓷原料等湿颗粒为典型物料，开展过热蒸汽和热空气流化床干燥动力学对比实验，验证优化干燥过程数学模型；进行不同工况下的过热蒸汽蒸汽流化床干燥过程数值模拟仿真，揭示操作压力、入口过热蒸汽温度、表观流速等重要参数对干燥过程的影响规律，形成更精确的过热蒸汽流化床干燥特性定量分析与过程优化控制方法，为过热蒸汽流化床干燥技术创新发展提供理论指导。

过热蒸汽流化床干燥是一项新型高效干燥技术，在农产品加工、化工及陶瓷工业等行业有重要的应用前景，然而其干燥过程复杂，热质传递机理尚不清晰，干燥过程中气粒两相流动与传热传质之间的耦合机制难于准确描述。本项目以过热蒸汽的凝结性和可压缩性等物性分析为切入点，探析了过热蒸汽流化床干燥过程中过热蒸汽与物料湿分之间的热质传递机制。基于CFD方法，构建了干燥过程传热传质数理模型，以油菜籽等颗粒物料为典型物料，开展了过热蒸汽流化床干燥流化实验、干燥动力学实验，验证优化了干燥过程传热传质机理模型；在模型验证的基础上，对过热蒸汽流化床干燥过程进行了数值模拟仿真，揭示了不同物理模型、操作压力、过热蒸汽温度和表观速度等重要参数对干燥过程的影响规律，形成了干燥特性定量分析与过程优化控制方法，为过热蒸汽流化床干燥技术的工业化应用及创新发展提供了理论指导。