Numerical study of blockage and arching behavior of particle with different shapes in packed bed

Abstract

Blockage has a significant impact on the flow and heat transfer characteristics of particles in discharging process and can affect the system security seriously. In this study, the discrete element method (DEM) was adopted to analyze the discharge flow of pebbles, ellipsoids, and cubes. The mechanism of blockage formation is the mechanical interaction between particles. With the increase of axial force, the frequency of the blockage increases. High probability of blockage formation arises when the local axial velocity difference dvzl is less than 0.075, while a large local difference in axial velocity (dvzl≥ 0.075) can efficiently avoid blockage. With the increase of the bottom cone angle α of the geometric of the packed bed, blockage during particle flow can be avoided. When α increased to 60°, the particles of Rd less than 0.248 can be discharged smoothly. In addition, the coefficient of friction μ between particles, the ratio of particle diameter to discharge orifice diameter Rd and the aspect ratio Ra of non-spherical particles are all factors influencing the formation of blockages. The critical conditions for particle blockage formation were proposed. For actual working condition of engineering, the application of Rd less than 0.24 and μ less than 0.4 can effectively avoid blockage formation and ensure relatively safe operation for spherical particle systems. For ellipsoidal particles, low aspect ratio (Ra≤4) can effectively avoid blockage.