Gas fluidization of nanoparticles
Department of Mechanical Engineering
Doctor of Philosophy
Dave, Rajesh N.
Ho, Teh C.
Circulating fluidized bed
The primary objective of this study is to perform a systematic investigation on the gas fluidization of various nanoparticle agglomerates. Firstly, the gas fluidization characteristics and regime classifications without any additional external force fields are identified using both experimental measurements and modeling. Secondly, the effect of introducing certain external force fields on nanoparticle fluidization is experimentally investigated. Two external force fields were applied: sound waves from a loud speaker (acoustic assistance) and in-bed magnets that were excited by an external oscillating magnetic field (magnetic assistance). Thirdly, exploratory experimental research on the use of nanoparticle agglomerates as a granular filtration media for airborne fine particles is conducted. The last part of this dissertation is an exploratory modeling study to interpret the newly-found core-annulus-wall flow structure in gas fluidization.
The experimental study on the gas fluidization of nanoparticles shows that most nanoparticles can be fluidized in the form of nanoparticle agglomerates. For those agglomerates (fluffy carbon black and very large agglomerates) that are difficult to fluidize, channeling always occurs. For those nanoparticle agglomerates that can be fluidized, the fluidization behaviors can be classified into two general categories, namely, agglomerate particulate fluidization (APF) and agglomerate bubbling fluidization (ABF). The classification appears to be depend mainly on the primary nanoparticle size and the bulk density.
Nanoparticle agglomerates have a special structure with extremely high porosity. In this study, an analytical model is developed to calculate the flow partition through and around the porous agglomerates, as well as the drag force on an agglomerate of nanoparticles in a swarm of other similar agglomerates. Also, an analytical model based on the Richardson-Zaki equation has been developed to predict the fluidizing agglomerate size, the voidage around the agglomerates, and the minimum fluidization velocities of APF nanoparticles.
The introduction of an external field such as sound excitation and magnetic excitation with in-bed magnets can significantly change the fluidization characteristics of nanoagglomerates, including a significant reduction in the minimum fluidization velocity and agglomerate size. The intensity and frequency of the external sound and magnetic fields will influence the fluidization quality of the nanoparticles.
In this study, a series of exploratory experiments have been conducted to remove sub-micron particles (including solid particles and liquid droplets) generated by burning incense. The results show that nanoparticle agglomerates in a packed bed can be used successfully as a filter media for airborne submicron particulates.
In addition, this study interprets the formation mechanism of the recently discovered core-annulus-wall structure in a circulating fluidized bed, which originates from the wall region mixing of a down flow of solids from the top section of a riser and the upward solids flow near the bottom of the riser, and the strong solid particle collisions in the dense phase suspension. A mathematic model of this phenomenon has been successfully developed and solved numerically.
njit-etd2005-090 (194 pages ~ 16,941 KB pdf)
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Created December 1, 2005