基于动态平衡预测纳米颗粒流化床内聚团尺寸分布

Prediction of the Agglomerates Size Distribution in the Nanoparticle Fluidized Bed Based on Dynamic Equilibrium

准确预测纳米颗粒流化床内聚团尺寸对研究纳米颗粒流化具有重要意义。鉴于目前文献中主要根据力平衡模型得出聚团尺寸平均值,然而聚团尺寸实际呈宽筛分分布,本工作从动态平衡角度,采用分子动理论中麦克斯韦气体速率分布律类比流化床内聚团速度分布,建立基于微观作用力的聚团解聚—重聚模型,并用以预测纳米颗粒流化床内聚团尺寸分布。通过比较聚团间结合力和分离力的相对大小,判断聚团结合和破碎;在分离力中,碰撞力起着至关重要的作用,且与聚团相对运动速度关系密切。预测结果显示,纳米颗粒流化床内聚团尺寸呈现卡方分布。将模型预测值和文献中的实验数据进行对比,包括TiO_2、Ni、SiO_2等颗粒的团聚尺寸,发现大部分偏差在20%以内。

It is important to accurately predict the size of the nanoparticle agglomerates in the study of nanoparticle fluidization. Currently, the average size of aggregates is mainly obtained from the force equilibrium model in the literature. However, the actual agglomerates in the fluidized bed have a very broad particle size distribution（PSD）. In this study, a dynamic equilibrium method has been proposed to predict the PSD of agglomerates by applying the Maxwell velocity distribution law of the gas molecular kinetic theory into the fluidized bed to develop the model of agglomeration-breakage and reunion based on the microscopic force. By comparing the relative magnitude of the binding force and the separation force, the agglomeration and fragmentation were judged. In the separation force, the collision force played a vital role, and was closely related to the relative velocity of agglomeration. The results showed that the PSD of agglomerates in the fluidized bed of nanoparticles shows a chi-square distribution. The comparison was made between the model predictions and experimental data in the literature, including the agglomeration size of TiO2, Ni, SiO2 particles, and found that most of the errors were within 20%.