Numerical And Experimental Study Of Gas-Solid Two Phase Flow With Non-spherical Particles In Typical Fluidized Beds

Gas fluidized bed with non-spherical particles is widely used in various industrial processes. However, researchers usually used the spherical hypothesis to simplify the model. Inevitably, deviations will be introduced, especially for the anisotropic characteristics of particles. It is of great significance to understand the micro mechanisms and macro dynamic characteristics of the behaviors of non-spherical particles. Related researches have been conducted with the soft-sphere approach of Discrete Element Method(DEM), but the mechanism of non-spherical particle system still needs further investigations.In this work, a complete numerical framework has been built to deal with the problem of non-spherical particles in gas-solid two-phase particle systems based on the hard-sphere approach of DEM. Based on a multi-element model, the kinematic model, a contact detection method, a collision model and a mechanical model are proposed. Quaternions and classic rigid body dynamics are employed and improved in this work, and new algorithms including a two-segment contact detection approach are established. The Current work takes into consideration efficiency along with accuracy, which makes the simulations at an experimental scale reliable. The collision model is based on Routh graphical method, coupling with the Possion restitution coefficient hypothesis and the Coulumb friction law.Based on the PIV system, the measurement on a spout fluid bed is conducted, and the DEM numerical simulation is carried out on the gas-solid two-phase flow of the non-spherical particles under corresponding conditions. The results show that in non-spherical particle systems, the mixing of particles is enhanced, and the elutriation is obvious. In addition, individual particles are in and around the bubbles. By comparing the experimental data and the numerical results, it is found the DEM numerical simulation predicts PIV experimental results accurately. The established DEM hard-sphere model for non-spherical particles is of favorable applicability.The DEM model built for non-spherical particle systems is applied to simulate the hydrodynamics behavior in a bubbling fluidized bed, spouted fluid bed and riser. For bubbling fluidized bed, as a simple gas-solid particle system, the particle behavior is typical. First, the spherical method is applied to investigate the particle behaviors in the bubbling fluidized bed, and the researches on particle behaviors under different gravities are conducted. Then the bubbling fluidized bed with non-spherical particles is simulated, and the comparison of particle behaviors between spherical and non-spherical particles are studied. For the monocomponent solid case, the periodic rules in the system with non-spherical case are more complex. Individual particles are in and around the bubbles, and the turbulent movement of bubbles is complex. For binary solid, the mixing is enhanced, and the turbulent movement in non-spherical particle systems of bubbles is stronger than the case of spherical particles.The model is also applied to simulate the hydrodynamics behavior of non-spherical particle systems in a spout-fluid bed. By using the region dependent method, the spatial relationship of particle behaviors is obtained. It is found that the partitions are different in the spherical and non-spherical particle systems. For the spherical cases, the center is the middle of bed, and different parts of fluidization behaviors are annular-distributed. But for the non-spherical case, the partitions are layered. The different partitions in spherical and non-spherical spouted bed indicate that there are different particle behaviors in the two beds. Compared the granular temperature distribution of spherical particles with the non-spherical particles, it can be seen that the turbulent movement of non-spherical particles is more violent. In addition, different bubble behaviors are presented.For the riser, the new concept of cluster granular temperature is proposed to investigate the turbulent movement of clusters in the system. For spherical particles, the difference of cluster granular temperatures under different drag models is obvious. The one of large particles is more concentrated, and it is opposite for the small particles. For non-spherical particle systems, the turbulent movement of clusters is weaker, and the cluster granular temperature of small particles is larger than that of large particles. That means the turbulent movement of small particles is stronger.