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

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To make the basic study for the flow control of clustering flows the effects of particle size distribution on the structure of the clustering flow is studied. Numerical simulations are performed for the gas-solid flows in a rectangular-parallelepiped calculation domain surrounded by periodic boundaries. The fluid motion is calculated by using DNS, while, the solid flow is calculated by using a Lagrangian model with considering the particle-particle collision. Furthermore, an experiment on the granular sedimentation flows in a vertical duct is performed to measure the structure of particle clusters and to validate the present simulation. In the experiment, the spatial structure of clusters are measured by a laser-sheet visualization equipment, the time series of solid volume fraction by a fiber-optic particle concentration measuring system, the velocities of the gas and the particles by a phase Doppler anemometer.The obtained results are summarized as follows.(1) In the case with particle size distribution, the present numerical simulation gives the larger clusters compared with those without particle size distribution. In addition, the particle size distribution reduces the fluctuation of the local solid volume fraction.(2) The measurement of the corresponding experiment demonstrated that the present numerical model with particle size distribution gives the better prediction about the cluster structure than that without it.(3) In the numerical simulation, the development of the particle clusters is much suppressed by the effect of the particle size distribution. It is considered that this suppression of the cluster development is caused by the particle diffusion due to the particle-velocity fluctuation made by the size distribution.(4) The present numerical model predicts that the larger particles make the larger clusters.