Numerical Simulation Of Liquid-Solid Two Phase Flow In Underwater Pelletizer

Underwater pelletizing machine is the key equipment of the large-scale extruding granulators group. Determining whether cutting out both neat and unified qualified resin particles. However, if particles accumulate inside the water chamber more serious,it will bring out two problems. On the one hand, it will cause the resin particles are secondary cutting by rotary cutter, affect product quality; Particles accumulate, on the other hand, easy to cause large extruding and granulating machine group parking, bring huge economic losses.This article using computational fluid dynamics software Fluent, the flow field inside the water chamber is simulated adopting RNG k-ε model, the particle trajectory and packing particles’number are also simulated with discrete phase model(DPM). Analysis of the particle residence time in the water chamber and the accumulation of the number of particles affectted by following parameters,such as inlet flow rate, rotating cutter speed, water chamber exit angle, height of convexs, convex platform radius size. Through a large number of numerical simulation research, basically have the following conclusion:(1) Obtain the flow field of the cutting chamber, by using PIV technique and Fluent software. Through experimental data and numerical simulation results analysis, we obtain the simulation results are agreed with the experimental data. The RNG k-ε model we chosen can accurately analysis the flow field in the water chamber.(2) Through continuous field of numerical analysis, we found that the flow field forced vortex nearly located in the center of radial water chamber, its intensity and size will increase as the cutter speed raise, however, its intensity and size decrease as the inlet flow increase. We also found that the flow field forced vortex nearly located in the center of tangential water chamber, its intensity and size will increase as the cutter speed raise, however, its intensity increase and size decrease as the inlet flow increase.(3) Face to the engineering problem,using DPM model to make numerical simulation.we come to the conclusion:For the radial feed way, cutting speed with400r/min, circulating water inlet flow with450m3/h, is a set of optimized parameters; For the tangential feed way, when the cutting speed is400r/min, inlet flow should better to reduce, this article take250m3/h;(4) By adjust the angential water chamber structure, we concluded that the average residence time and the number of remaining particles will gradually reduce with the export angle decreases, export angle for zero, is the best to optimize. Convex platform height increase, will be helpful for more particles out of water chamber, this article take the best convex platform height is260mm; Larger radius of convex platform can significantly reduce the number of particles. This article take the best convex platform radius size is170mm.Through the theoretical research, the test and analysis of experiment and numerical simulation of the water chamber of underwater pelletizer, the results provide the technical guidance for pelletizing plant transformation. Also this article lays a foundation for the theoretical research and practical application.