埋管流化床内传热行为的微观尺度模拟研究

为了模拟埋管流化床内的流动和传热行为,将有限元方法(FEM)、基于非结构化网格的计算流体力学方法(CFD)与离散单元法(DEM)结合,建立了CFD-DEM-FEM耦合方法,并在此基础上采用k-ε湍流模型及考虑颗粒间和气固间作用的多向耦合传热模型.通过计算结果从微观尺度探讨了埋管流化床内的传热机制,分析影响床内传热的关键因素,得到换热管壁周围固含率和传热系数的分布规律,考察了流化气速对埋管周围传热系数的影响.数值模拟结果与实验结果基本一致,证实了CFD-DEM-FEM耦合方法模拟复杂气固流动和传热的可行性和准确性,为进一步了解流化床内热传递行为的机理、准确预测各种流化床内的传热以及开展流化床内多尺度流动-传热-反应流的模拟奠定基础.

Micro-scale simulation of heat transfer behavior in fluidized bed with immersed tube

A new coupling method, CFD-DEM-FEM method, was founded by combining finite element method (FEM), computational fluid dynamics (CFD) based on unstructured mesh, and discrete element method (DEM). The flow and the heat transfer behaviors in the fluidized bed with immersed tube were simulated by the programs based on the new method when the k ε turbulence model and the multi-way coupling heat transfer model among particles, tube wall and gas were employed. The micro scale mechanism of heat transfer in the fluidized bed was explored by the simulation results and the critical factors that influence the heat transfer between the tube and the bed were discussed. The profiles of average solids fraction and heat transfer coefficient around the tube were obtained and the influence of gas velocity on the transfer coefficient was revealed by simulation. The computational results agree well with the experimental data, which shows that the CFD-DEM-FEM method is feasible and accurate for the simulation of complex gas solid flow with heat transfer. And this will improve the further simulation study of the gas solid two phase flow with chemical reactions in the fluidized bed.