Study on the Meso-Scale Particle Structure formed in Gas-Solid Flow

点击翻译按钮获取中文摘要

Gas-solid flows with particle clusters were studied. Numerical simulations were performed for the gas-solid flows in a rectangular-parallelepiped calculation domain surrounded by periodic bound-aries. Fluid motion was calculated by using DNS and LES, in which the same SGS model as in single-phase flows was assumed. Solid flow was calculated by the Lagrangian method, in which the motion of individual particles was tracked, with considering particle-particle collisions. Furthermore, an experiment on the granular sedimenting flows in a vertical duct was performed to measure the structure of particle clusters and to validate the present simulation. The results are summarized as follows.1. The present LES and DNS predicted the formation of particle clusters. Effects of mean solid- volume fraction (SVF) and fluid viscosity on the flow structure were examined. It was found that, in the case of mean SVF of 10^<-5>, the formation of particle clusters was observed, but it takes much longer time … More than the higher fraction cases. The spatial scale of particle clusters decreased with increasing the fluid viscosity. We examined the smallest eddy scale in the present simulation results and found that DNS had performed for the present calculation conditions.2. It was found that the fully developed flows were established in the lower region of the duct. The structure of particle clusters in vertical and horizontal planes were observed by using laser-sheet visualization technique. The structure of clusters observed is like a network of strands and similar to both of the present numerical predictions and previous experiments in risers of CFB.Distributions of the solid volume fraction in the duct cross-section was measured. It was found that particles tend to concentrate to duct walls and this tendency is enhanced in high solid flow rate.3. The measured fluctuation pattern of the local SVF is similar to the present predictions. The profile of probability density function of the measured SVF agrees well with the predictions. Power spectrum of fluctuation of the measured SVF agrees qualitatively with the predictions, but quantitatively, fairly well. Less