Enhanced fluidization of nanoparticle agglomerates
Otto H. York Department of Chemical, Biological and Pharmaceutical Engineering
Doctor of Philosophy
Dave, Rajesh N.
Armenante, Piero M.
Loney, Norman W.
Gas fluidization of nanoparticle agglomerates has recently received much attention due to the excellent way in which these novel nanornaterials can be dispersed in a gaseous medium. Nanopowders have a very high surface area to volume ratio which allows them have unique chemical and physical properties especially at the surface. Fluidization is a popular technique for the continuous dispersal of solid materials in the fluidlike state.
Recently it has been found that nanoparticles exist in a highly agglomerate state which allow them to become fluidizable. The fluidization behavior of the nanopowders is dependent on the bulk and material properties of the powder. Although some nanopowders can become fluidized in the particulate fluidization state, others are unable to be fluidized homogeneously.
Nitrogen and neon were used as fluidizing gases to study the affect of gas viscosity on the fluidization state of nanopowders. For the nanopowders used, it was found that the increased viscosity of the fluidizing gas helps to dampen any disturbances to the flow structure of the fluidized bed. A more viscous gas minimizes the size of bubbles, thereby extending the regime of homogeneous fluidization by suppressing the onset of the bubbling regime. Laser-based imaging and microscopy techniques were also used to study the agglomerate size and structure within the fluidized bed.
Vibration and electrostatic fields were applied to a fluidized bed of nanoparticle agglomerates to observe any changes in bed expansion and flow behavior. Applied vibrational intensities were found to increase the expansion of the fluidized bed, although large bubbles were observed at low vibrational frequencies. Electrostatic fields were found to decrease the expansion of the fluidized bed due to the induced charge on the powder and their migration to the fluidization cell walls. Combined vibration and electrostatic fields were applied and it was observed that the bed height of the fluidized bed can be controlled as a function of the strengths of the external fields.
Three different arrangements of alternating electric fields were used to enhance the fluidization of a nanofluidized bed. All arrangements were found to increase bed expansion of the fluidized bed. In particular, the non-uniform electric field arrangement was found to be successful in fluidizing a wide range of agglomerate size distributions of the nanopowder.
njit-etd2009-008 (180 pages ~ 15,811 KB pdf)
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Created November 1, 2010