Simulation of Particle Motion Behavior in Fluidized Bed Opposed Jet Mill

In order to study the influence of the internal flow field of the fluidized bed opposed jet mill on the motion behavior of particles, Computational Fluid Dynamics (CFD) and Discrete Dlement Method (DEM) are used for coupling calculations. By adjusting the nozzle spacing and inlet pressure, Numerical simulation is carried out on the process of particles collisions with each other after accelerating under the high-speed jet produced by the nozzle. The trajectory of the particles in the flow field of the collision area and the change of the collision state of the particles are analyzed. Finally, the best parameters are selected based on the total collision energy. The results show that the particles will gradually shift and spread during the acceleration process. The reduction of the nozzle spacing is beneficial to increase the probability of particle collisions. However, if the spacing is too small, the particles cannot be fully accelerated; the increase in inlet pressure will increase the kinetic energy of the particles, and number of collisions is almost unaffected. By comparing the total collision energy, the best-simulated preparation conditions are selected as 110mm and 1.1MPa.

Flow Characteristics of a Model Can-Type Combustor

Numerical simulations are performed on a can-type combustor in order to indentify various flow features. Elementary flow features like jet-in-crossflow, opposed jets, swirl and recirculation zones are present in a combined form. Momentum flux ratio between axial air flow and radial primary air jets from the circumference of the combustor is an important parameter. While increasing mass flow rate of the radial jet, the jet-in-cross flow structure changes to opposed jet. Swirl of axial jet is favourable for opposed jet configuration. A step provided at the close vicinity of the primary jet allows the primary jet expansion and its flow structure is affected at the entrance of the combustor to favour for jet-in-cross flow configuration. The opposed jet configuration provides large recirculation at the upstream due to merging of vortices arising from swirl of axial jet and upstream movement of primary air jet. This helps in holding the flame and also for effective combustion. However, there is a lower temperature region at the downstream core of the combustor due to penetration of primary air jets. On the other hand, jet-in-crossflow configuration has shown hotter zone at the downstream core of the combustor. Hence, effective utilization of flow structure can be considered in future design.

CFD-DEM Simulations of Graphite Particle Collisions in Opposed Jet Mill

Graphite is widely used in nuclear reactors as moderator and structural material. Among present graphite preparation methods, air flow mill is considered to be qualified in the control of particle size and purity, and promising for future mass production. In this work, an opposed jet mill is designed to crush large graphite particles. The opposed jet mill accelerates the particles through two supersonic jet flows in opposite directions, and finally the particles collide in the crushing cavity. In order to estimate the performance of opposed jet mill, it is necessary to solve the coupling calculation of the compressible flow and the collision process of discrete particles. However, the research on calculating the compressible gas solid coupling problems is scarcely rare. In this paper, coupled CFD-DEM model is used to simulate the particle movement process with jet flows and accompanying jet in opposed jet mill. By comparing with experimental results, it is proved that these simulation results of the acceleration process of compressible gas through these nozzles and the collision process of the final two supersonic jet flows in the opposed-jet mill are accurate, with the accuracy model of the coupled CFD-DEM provided. The practice has proved that the contrastive flow mill has a broad application prospect in the production of graphite particles.