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Particle Lagrangian CFD Simulation and Experimental Characterization of the Rounding of Polymer Particles in a Downer Reactor with Direct Heating

机译:粒子拉格朗日CFD仿真和实验表征在直接加热中沿越热反应器中的聚合物颗粒圆角的实验表征

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摘要

Polypropylene (PP) powders are rounded at different conditions in a downer reactor with direct heating. The particles are fed through a single central tube, while the preheated sheath gas is fed coaxially surrounding the central aerosol jet. The influence of the process parameters on the quality of the powder product in terms of particle shape and size is analyzed by correlating the experimental results with the flow pattern, residence time distribution of the particles and temperature distribution predicted by computational fluid dynamics (CFD) simulations. An Eulerian–Lagrangian numerical approach is used to capture the effect of the particle size distribution on the particle dynamics and the degree of rounding. The simulation results reveal that inlet effects lead to inhomogeneous particle radial distributions along the total length of the downer. The configuration of particle/gas injection also leads to fast dispersion of the particles in direction of the wall and to particle segregation by size. Broad particle residence time distributions are obtained due to broad particle size distribution of the powders and the particles dispersion towards the wall. Lower mass flow ratios of aerosol to sheath gas are useful to reduce the particle dispersion and produce more homogenous residence time distributions. The particles’ residence time at temperatures above the polymer’s melting onset is determined from the simulations. This time accounts for the effective treatment (rounding) time of the particles. Clear correlations are observed between the numerically determined effective rounding time distributions and the progress of shape modification on the particles determined experimentally.
机译:聚丙烯(PP)粉末在不同的条件下圆形反应器的不同条件,直接加热。颗粒通过单个中心管进料,而预热的鞘气体被同轴地围绕中央气溶胶射流进料。通过将实验结果与流动模式(CFD)模拟预测的颗粒(CFD)模拟预测的颗粒(CFD)模拟预测的实验结果,通过将实验结果与颗粒形状和大小进行粒子形状和尺寸来对粉末产品质量的影响。通过计算流体动力学(CFD)模拟预测的颗粒(CFD)模拟。 Eulerian-Lagrangian数值方法用于捕获粒度分布对粒子动力学和舍入程度的影响。仿真结果表明,入口效应导致沿下越长的颗粒径向分布。颗粒/气体喷射的构造也导致颗粒在壁方向上的快速分散并通过尺寸来颗粒偏析。由于粉末的宽粒度分布和朝向壁的颗粒分散而获得宽颗粒停留时间分布。较低的气溶胶到鞘气体的质量流量比可用于减少颗粒分散体并产生更均匀的停留时间分布。从模拟中确定聚合物熔化发作的温度下的颗粒停留时间。这次占颗粒的有效治疗(舍入)时间。在数值确定的有效舍入时间分布和实验确定的颗粒上的形状改性的进展之间观察到清晰的相关性。

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