煤粉粒径对密相气力输送流型影响的数值模拟

针对目前密相气力输送数值模拟过程中所存在的关键问题,提出了一种描述固相内部相互作用对颗粒运动影响的数学模型,采用该模型能够对稠密气固两相流动(乃至颗粒发生大量沉积的情况)进行数值模拟.新模型在离散颗粒模型的基础上,通过描述颗粒所在局部空间的固相浓度及颗粒群运动特征所建立,使其既能够模拟悬浮流动的稀相颗粒运动,又能模拟管内出现堆积情况的密相气固两相流.利用所建立的数学模型对高压密相煤粉气力输送的颗粒流动过程进行了数值模拟.模拟结果显示,随着颗粒粒径增大,粉体密相气力输送流型从沉积层流变化为沙丘流,进而演变成栓塞流的演变过程,并结合实验验证了典型的栓塞流、沙丘流等流型特征;并且平均栓塞长度随着粒径的增大而减小,而随着粉体粒径的增大,输送管道中固相容积份额则整体上呈增大趋势.

Numerical Simulation of Flow Regime in Dense-Phase Pneumatic Conveying with Different Pulverized Coal Particle Sizes

The key problems of current numerical simulation of dense-phase pneumatic conveying were analyzed in this paper.To solve these problems,a new mathematical model for describing the contact force between particles was proposed,and the dense-phase gas-solid two-phase flow(even when the particles packed)could be simulated by the new model.Based on discrete particle modle(DEM),the new model used the solid phase volume concentration and the characteristics of particle motion to describe the contact force between particles to make sure that the new model can not only simulate dilute phase flow like dispersed flow regime but also dense gas-solid two-phase flow(even when the particles packed).The new model was used to numerically study the flow behaviors of dense phase pneumatic conveying at high pressure.The typical flow regimes,such as slug flow and dune flow which agreed well with experimental results,were obtained,and with the increase of particle size,the flow regime of pulverized coal in dense-phase pneumatic conveying changed into dune flow from sedimentation flow and then changed into slug flow from dune flow.The mean slug length decreased while the average solid concentration in horizontal pipe increased with the increase of particle size.