| This study is conducted to understand the fundamental questions of the dense gas-particle jet and to develop a numerical model. Using high speed camera, software of particle image velocimetry, and Fluent software, the characteristics of particles dispersion and particles motion are studied through experiment and simulation on the basis of pulverized coal gasification. The main contents and results are summartized as follows:1. The dispersion characteristics of the granular jet are obtanined using a high speed camera. The results show that the surperfical velocity of particles plays an important role in the characteristics of the near field of the granular jet (e.g., the diameter of granular jet core, the width of dispersed jet, and the thickness of boundary layer). The width of dispersed jet and the thickness of boundary layer linearly grow with the distance from the nozzle exit at first and then keep a constant. The velocity profile of boundary layer near the nozzle exit is parabolic distribution. In addition, the nozzle angle has an influence on the radial velocity of particles and sequentially affects the characteristics of the particle dispersion.2. The dispersion characteristics of the granular jet in the parallel-nozzle and cross-nozzle are analyzed. The dispersion modes in the parallel-nozzle are also analyzed. The calculational formula of the undistured length is obtained by analyzing the force acting on the particles. An entrainment model is used to calculate the dispersion length and the model successfully predicts the dispersion length. The minimum diameter of granular jet and its appearing-position are obtained by analyzing the granular jet in cross air jet and their calculational formulas are also obtained. It is found that the Strouhal number, Sth, can be used to distinguish the dispersion modes of the granular jet, when0.07> Sth>0.03, it belongs to the wave dispersion mode, when0.02> Sth>0.01, it belongs to the oscillating mode, and when0.03> Sth>0.02, it belongs to the transition state between the wave dispersion and the oscillating dispersion.3. The dispersion of the particles is invesgated by the numerical simulation. The Realizable k-ε model is used to model turbulence. The discrete particle method is employed to track particle motion and the probability-collision is used to consider the inter-particle collision. The results show that the axial velocity of air increses with the increase of the cross angle and will increase to a max value. The turbulent kinetic energy is highest on the interface between granular flow and air flow, which is in favor of the particle dispersion. The particle concentration decreases along the axial direction as a whole, and its profile agree with the Gauss function in the radial direction. The collision among particles is the most intense on the interface of the granular jet.4. A2D LES-DPM (large eddy simulation-discrete particle method) is developed to take account the dispersion modes of the granular jet in a parallel coaxial air. The void fraction and the iner-particle collision is introduced into the Fluent through re-organize the gas phase equations in Fluent. The global features of the flow field are obtained. It is found that there is invese flow between the air jet and granular jet near the nozzle, which would make the particles take off the interface of the granular jet and then wear the nozzle. The air velocity, particle velocity, particle concentration and the frequency of the collision between particles are also obtained. It is found that the above characteristics can reflect the state of the dispersion of the granular jet. By analyzing the interaction between air and particles (including the no linear of the drag coefficient and the operating pressure) and the inter-particle collision (or transmission of the energy between particles), the mechanics of the dispersion of the granular jet is investigated. The results suggest that both of the two interactions are important for the dispersion modes, and the nolinear of the drag cofficicent is dominant. |
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