Study Of Two-Phase Flow Characteristics In A SMTD Dryer

The study of SMTD(swirl medium time dryer)is extremely difficult for its complicated interior flow field as well as lacking theoretical and experimental researches. In this paper, the SMTD dryer was preliminarily studied by computer simulation.The velocity field of gas-solid flow in SMTD dryer was simulated by the method of computational fluid dynamics (CFD). And the single-phase flow field, gas-solid flow field, particle volume fraction, particle motion track, pressure drop, temperature field and moisture distribution were investigated in this paper.The gas flow field was simulated by the use of three models: thek ?εstandard model, RNG model and Reynolds stress model (RSM model). The results show that the RSM model is more suitable, so in this paper, the gas-solid flow was coupling calculated by using the RSM model.The distributional characteristics of the three- dimensional component velocity of axial direction, radial direction, and tangential direction of the velocity field in the SMTD dryer were obtained by the simulation. The result indicates that tangential velocity is the main velocity among the three as it's much larger than the others. Then the characteristic of the distribution of pressure and relationship between pressure and gas velocity were further analyzed.Euler coordinate RSM model was used for the gas simulation. The particles were calculated respectively using mixture model under Euler coordinate and stochastic model under Lagrange coordinate. At the same time the interaction of two phases was considered. The distribution of solid particles was obtained by Euler model. The result shows that the volume fraction of solid particles reaches the highest value on the wall and increases with the increasing radial distance. The particle trajectories were presented by the Stochastic model. The result indicates the movement of particles in the dryer is randomness. The gas temperature falls with the increase of dryer height while water vapor concentration increases with the increase of dryer height. Near the wall,water vapor concentration is higher.In order to get a better understanding of the flow characteristics of SMTD dryer, the particles residence time in the dryer was researched. The results of simulation agree very well to experiment data, which proves the correctness of simulation and can make contribution to further design and theoretical research of SMTD dryer.