Study On The Hydrodynamics And Heat Transfer Characteristics Of Gas-solid Flow In Spouted Bed

Spouted beds have been widely used in chemical industry, energy, agriculture, medicine and other industries applications due to their superior heat-and mass-transfer characteristics. Studying on the hydrodynamics and heat transfer characteristics of gas-solid flow in spouted beds has a practical significance on the quantitative design and reasonable control of spouted bed reactors.Based on using high-speed camera and PIV technology, a flat spouted bed experimental installation is built to study the flow characteristics of particles in spouted bed. The diagram of particles fluidized process in the spouted bed is obtained. The behavior of bubble and the particles in the spouted bed are analyzed. The results show that the bubble goes through the process of generating, enlarging, merging and bursting and a core-annular flow pattern is formed, where the particles move upward in the middle region of bed and move downward near the wall, the particles aggregate at the center in the bottom of bed and move towards both sides in the upper region. Based on the self-developed CFD-DEM program of gas-solid flow in the spouted bed, the current work develops the program to simulate the characteristics of heat transfer in the spouted bed. Solid particles are simulated based on the soft sphere model in this work. The gas phase is solved using SIMPLER approach. The coupling between the gas phase and the particles is based on the two-way coupling method. The mixing process, gas velocity profile, particles velocity profile and granular temperature distribution are obtained from the CFD-DEM simulation. The particles velocity field, gas velocity field, the mixing mechanisms, the granular temperature, the expansion height are discussed. The results indicate that the trends in velocity distribution of gas and particles are similar, the core-annular flow pattern is formed in the spouted bed, axial mixing quality may be better than that of radial direction and the increase of the superficial gas velocity promotes particles mixing, increase the granular temperature and heighten the expansion height. The characteristic of heat transfer in spouted bed is simulated at a particle scale in the CFD-DEM program. The sequence diagram of particle heat transfer, gas temperature distribution, particle temperature rise curve and heat transfer coefficient are obtained from the simulation. The temperature distribution of gas-solid, particle temperature rise curve and the heat transfer coefficient of different mechanisms are discussed. The results indicate that the spouted bed reactors have high heat transfer capability, the heating rate is large at the early stage and then it slows down gradually, the increase of the superficial gas velocity and the thermal conductivity of bed particles can promote the heat transfer in the spouted bed reactors and the contribution of radiation heat transfer is relatively small when the bed temperature is low.