【作者】 段蜀波；

【导师】 周勇；

【作者基本信息】 四川大学 ， 化学工程， 2005， 硕士

【摘要】 纳米颗粒由于尺寸微小,其表面结构和电子结构发生变化,从而表现出许多大块物料所不具有的表面效应、小尺寸效应、量子效应和宏观量子隧道效应,使纳米颗粒展现出许多特有的性质,在催化、滤光、光吸收、医药、磁介质及新材料等方面有着广阔的应用前景。作为一种强化气固接触的手段,流态化技术在纳米颗粒制备、处理和应用方面都具有独特的优越性,因此,纳米颗粒的流态化技术越来越受到人们重视,并对其展开了研究。本文以原生纳米级SiO₂超细颗粒为物料,首先在横截面130×10mm²的二维流化床和内径130mm的三维流化床中,考察了声波对纳米级SiO₂超细颗粒流化行为的影响,结果发现:在无声场引入时,纳米级SiO₂超细颗粒除在三维流化床中出现了活塞流以外,在二维、三维流化床中都出现了裂纹、沟流、聚团流化现象,最小流化速度较高,形成的聚团尺寸较大,流化质量差;而当引入适当频率的低频强声波,可以消除活塞流、抑制沟流现象,大大减小聚团尺寸、降低临界流化速度,从而显著改善纳米级SiO₂超细颗粒的流化质量;但另一方面,声场能促进气泡聚并长大,实验发现,在二维床中,当声压高于138dB时出现了节涌。本文还较系统了研究了原生纳米级SiO₂超细颗粒在声场流化床中的流化特性,结果表明:在频率一定的情况下,声压越高,流化床中形成的聚团尺寸越小,最小流化速度越低,流化质量越好;当声压低于120dB时,声场对更多还原

【Abstract】 The fluidized techniques of nano-particles are gaining increasing importance along with the great application of particles to the manufacture industry. But the fluidization of nano-particles easily results in channeling and poor fluidized behavior as a consequence of strong particle-to-particle cohesiveness. So various techniques have been proposed to improve the quality of fluidization of nano-particles. Especially, the sound-assisted fluidization of nano-particles is researched in this work. A two dimensional bed which cross section is 130×10mm² and a three dimensional bed which ID is 130mm are designed to study the effects of sound wave frequency and sound pressure level on the fluidization of the nano-particles. The SiO₂ nano-particles have been fluidized in the beds. The experimental results prove that the quality of fluidization of particles is dramatically improved by the application of acoustic field of appropriate SPLs, and the air bubbles grow bigger in the sound （when SPL up to 138 dB, the air bubbles become slugging fluidization in the two dimensional bed）. There are cracks , channels in the two dimensional bed and the three dimensional bed, and pistons in the three dimensional bed without sound. However, cracks, channels or pistons are disappear with sound. Especially the minimum fluidization velocity and the size of agglomerations have minimum values when the frequency of sound waves is 120Hz and they will decrease as the sound pressure level increases. A good quality of fluidization can exist in a greater ranges of frequency of sound when the SPL is higher. The theoretical calculations are accordant with the experimental results in the three dimensional bed and it shows that the theoretical model can successfully describe the influence of the acoustic field on fluidization of the particles by Liang etc.更多还原