纳米颗粒的流化特征及滞后现象研究

Study on Fluidization Characteristics and Hysteresis Phenomena of Nanoparticles

为研究纳米颗粒的流化特征以及滞后现象,通过实验考察SiO_2、Al_2O_3和TiO_2纳米颗粒的流化行为,详细比较了在纳米颗粒流化过程中正向和反向的流化状态及床层压降之间的差异.结果表明:在稳定流化状态下,3种纳米颗粒的床层压降和流化状态有所差异,SiO_2表现为聚团散式流态化,Al_2O_3和TiO_2表现为聚团鼓泡流态化;3种纳米颗粒的正向流化均出现了显著滞后,在正向流化过程中床层压降和膨胀高度波动较大,而反向流化时相对平稳;通过设计"正-反-正"流化实验,发现二次正向流化曲线与反向流化曲线几乎重合,没有出现滞后现象,说明初始床层纳米颗粒的堆积结构和内聚力是引起流化滞后的原因.

To study the fluidization characteristics and hysteresis phenomena of nanoparticles, the fluid- ization behavior of following nanopartieles was investigated experimentally, such as the SiO2, Al2O3 and TiO2 nanoparticles, so as to find the difference of fluidization state and bed pressure drop of nanoparticles in the forward and reverse flow. Results show that under stable fluidization conditions, above three particles are different in bed pressure drop and fluidization state; SiO2 fluidization exhibits in the agglomerate particulate form, while Al2O3 and TiO2 fluidization are of the agglomerate bubbling type. For above three nanoparticles, there is a significant hysteresis in forward fluidization compared with the reverse fluid- ization. In the process of forward fluidization, the bed pressure drop and the expansion height fluctuate greatly, which are relatively stable in the reverse flow. By means of the design of ＂forward-backward-for- ward＂ fluidization experiments, it has been found that there is no hysteresis in the secondary forward flow of nanoparticles compared with the reverse fluidization, indicating that the hysteresis phenomena are mainly caused by the structure and cohesion of nanoparticles in the initial bed.