固定床中丝状颗粒的传热传质特性

摘要

The knowledge on the heat and mass transfer characteristics of filamentous particles in a fixed bed is preliminary.This paper describes a numerical model for microscopic heat and mass transfer mechanisms between particles and between gas and particles at particle scale.The CFD-DEM coupled approach was employed to numerical study on the local flow and transfer information in the fixed bed,which is difficult to obtain from experiment.The critical factors influencing the temperature and moisture content distribution in a fixed bed such as the air inlet temperature and superficial gas velocity were examined.The model was validated by comparing the simulation results with experimental data.It is concluded that the temperature of filamentous particles reduces and the moisture content of particles increases with the increase of bed height.The air inlet temperature plays a dominant role in the average temperature of the bed,and the mass transfer rate of filamentous particles is affected more obviously by the superficial gas velocity.%目前对于固定床中丝状填充颗粒传热传质特性的认识仍处于初始阶段.为了能够从颗粒尺度的微观层面揭示丝状颗粒与气体、颗粒与颗粒之间的热、质传递机理,建立了一种丝状颗粒传热传质数学模型,之后将离散单元法与计算流体力学相结合,对实验中较难获得的床层局部流动及传递信息进行了数值模拟,并着重分析比较了气流入口温度以及表观气速等关键因素对固定床中丝状颗粒温度和含水率变化的影响规律.通过模拟结果与实验数据的对比,验证了所建模型的可行性.研究结果表明:同一时刻,固定床中颗粒温度大体上是随着床层高度的增加而降低,含水率则是随着床层高度的增加而升高;气流入口温度对于固定床中丝状颗粒平均温度的提升起着主导作用,而颗粒的传质速度则受表观气速的影响更为明显.