Experiments On Particle Rotation And Collision In Gas-Solid Fluidizing Beds

Gas-Solid Fluidizing beds have wide applications in the fields of Energy, Chemical and Environmental Engineering, the mechanism of which is always the emphasis and difficulty in energy utilization academic area. Particle rotation speed, Inter-particle collision and Particle-wall collision, which have been the emphasis in recent years, have much influence in distribution of porosity, Heat and Mass transfer characteristics and flow field around particle in gas-solid flow field. The objective of this thesis is studying the factor which affecting particle rotation speed, Inter-particle and Particle-wall collision rate in Gas-Solid Fluidizing Beds through the ways of experimental measurement.First, a high-speed digital imaging system was used to visualize the motion behavior of spherical glass beads in a micro-scale level with an average diameter of about0.3mm,0.5mm and0.7mm in the upper dilute zone of a cold Gas-Solid Fluidizing Beds with a dimension of105mm×45mm×1m. The high-speed digital imaging system is mainly composed of a high-speed digital camera, a high power laser and corresponding digital imaging processing procedures. The particle rotation and collision motions were investigated.And then, combined with statistical analysis, the experiment of studying the characteristics of particle rotation and collision rate in Gas-Solid Fluidizing Beds were carried out and the results are as follows:In the same region, the particle-particle and particle-wall collision rate is found to be proportional to the square of particle number density, which coincides with the collision theory derived according to the analogy of kinetic theory of gases. And then, when the average particle diameter increases from0.35mm to0.9mm, the particle-particle and particle-wall collision rate decrease from1900/s-1cm-3to1300/s-1cm-3and from2850/s-1cm-3to1000/s-1cm-3separately, and the average particle rotation speed decreases from135r/s to45r/s. It is shown that the average rotation speed of small particles is higher than that of large ones at the same operation condition, which is suitable for particles both near the wall area and center area. For the particles within the same size range, when the average horizontal translational velocity component of the particles increase from0.15m/s to0.24m/s, the particle-particle and particle-wall collision rate increase from1600/s-1cm-3to3000/s-1cm-3and from1950/s-1cm-3to3150/s-1cm-3separately, and the average particle rotation speed increases from90r/s to150r/s. It is found that the particles with relative higher horizontal translational velocity component may be found to be with higher rotation speed statistically. But the vertical translational velocity component of the particles may have a little effect on its rotation speed. And then, when the total amount of bed material are8mm,15mm and18mm, the average particle rotation speed are found to be70r/s,95r/s and105r/s in near wall areas. We can explain it as follows. As the total amount of bed material increases, more and more particles take part in the internal circulation. Therefore, the particle concentration and the particle collision rate increase. The effects of operation parameters on the average particle rotation speeds have also been investigated. The results show that the increased superficial gas velocity improves the average particles rotation speed near the wall area. The reason is probably that the particle concentration increases as well as the superficial gas velocity increases. Meanwhile, the character of the annulus-core flow is more significant. In the near-wall area, the increase of particle concentration leads to a rise in the particle collision rate. At last, the radial distribution of the average particle rotation speed is analyzed. It is shown that the average particle rotation speed increases at first and then decreases along with the direction from the inside wall to the center.