Numerical modeling of fluid and particle behaviors in impact pulverizer

作者：Takeuchi Hirohisa; Nakamura Hideya; Iwasaki Tomohiro; Watano Satoru^*

来源：Powder Technology, 2012, 217: 148-156.

DOI：10.1016/j.powtec.2011.10.021

• Impact pulverizer
• Numerical modeling
• Grinding
• CED
• DPM
• Two-phase flow

Numerical modeling of fluid flow and individual particle motion in an impact pulverizer was conducted using a Computational Fluid Dynamics (CFD)-Discrete Phase Model (DPM) coupling model. The impact pulverizer used is a dry system. Its grinding chamber consists of high-speed rotating hammers and a static concavo-convex stator. First of all, calculated results of fluid pressure in the grinding chamber were compared with the experimental ones, showing the both results were in good agreement. The fluid flow in the grinding chamber indicated that the fluid mainly swirled in the direction of the hammer rotation. The fluid flow pattern in the concaves of the stator was also swirling flow, while its velocity was much lower than that in the outside of the concaves. Analyses of the particle motion suggested that the particles were accelerated by the fluid drag force caused by the rotating hammers but not by the impact force from the hammers, resulting in impacts with the static stator at the velocity 1.4 times higher than the tip speed of hammers. The velocities and frequencies of the particle impacts with the walls of the grinding chamber were also investigated under various rotor speeds and particle sizes. As the particle size was smaller, the particle impacts with the stator were not likely to occur, and a decrease of the impact velocity was observed despite the same rotor speed. It was because the particle velocity decreased before impact with the stator due to the fluid resistance force acting on the particle in the concave. The fluid resistance force was proportional to the square of the particle size. By constant, an inertia force of the particle was proportional to the particle mass, which was equivalent to the cube of the particle size. Accordingly, the velocity of particle impact with the stator was lower when particle size was smaller. These calculated results implied that the limitations of ground particle size existed because of the decrease in the frequency and velocity when particle size was smaller.

• 出版日期2012-2