Fluidization of fine and ultrafine particles using nitrogen and neon as fluidizing gases

Abstract

in Wiley InterScience (www.interscience.wiley.com).When fluidized by a gas, some agglomerated fine and ultrafine particles display a regime of uniform, nonbubbling fluidization known as agglomerate particulate fluidization (APF). The agglomeration of micrometric sized particles, or simple pre-existing agglomerates in the case of nanoparticles, is governed by the balance between hydrodynamic shear forces and interparticle attractive forces. From this balance the theoretical scaling law Bo g $ k D12 has been derived, where Bo g , the granular Bond number, is the ratio of the interparticle attractive force to particle weight, k is the ratio of agglomerate to particle size, and D is the fractal dimension. In the experimental program the behavior of gas-fluidized beds of fine and ultrafine particles as affected by the use of neon and nitrogen as fluidizing gas is studied. The experimental results indicate that there is no relevant distinction between the sizes of agglomerates fluidized with the different gases as theoretically predicted. However, it is seen that the relatively small increment of gas viscosity opens up a new window of highly expanded agglomerate particulate fluidization (APF) behavior with a delayed onset of bubbling. For a sufficiently high-gas viscosity, and/or smaller particle size, full suppression of the bubbling regime is observed. For nanoparticles exhibiting agglomerate bubbling fluidization (ABF) behavior, where bed expansion is small, and bubbling occurs soon after minimum fluidization, we also observe a delayed onset of bubbling when fluidizing with a gas of higher viscosity.

Nanofluidization as affected by vibration and electrostatic fields

“…Eq. (1) has been fitted to experimental data, which has served to infer an average value of the agglomerate size in fluidized beds, which has yielded results in accordance with independent direct experimental observations (Castellanos et al, 2001;Nam et al, 2004;Zhu et al, 2005;Valverde et al, 2008). Yao et al (2002) observed that 7-16 nm silica particles formed multi-stage agglomerates (MSA) in the fluidized bed by three steps.…”

“…From these values it is calculated F * vdW ∼ 10 nN. Using a typical value of d * =30 m for the size of the simple-agglomerates, as inferred from the work of Nam et al (2004), and D a = 2.5, as inferred from settling experiments Valverde et al, 2008;Wang et al, 2006a), Eq. (2) predicts d * * 150 m for 10 nm silica nanoparticles ( p = 2500 kg/m 3 ).…”

Model for Calculation of Agglomerate Sizes of Nanoparticles in a Vibro‐fluidized Bed

“…The vibration energy is mostly absorbed by the agglomerates on the surface of the fluidized bed [22]. Even though the Richardson-Zaki equation has mainly been applied to describe the bed expansion of liquid fluidized beds [6], its general form has also been successfully applied to beds exhibiting strong interparticle forces [11,15,19,23]. The equation relates the superficial fluid velocity, U g , with the bed voidage, e, and the terminal velocity for a single particle, U t , as given by Eq.…”

“…Valverde et al [7][8][9][10] extensively explored this approach based on a modified Richardson-Zaki equation to estimate the subagglomerate size. Following this, the method was used to estimate the agglomerate sizes of nanoparticles [11].…”

Deagglomeration of nanoparticle aggregates via rapid expansion of supercritical or high‐pressure suspensions

“…4,5,48 Although the fractal dimension is often treated as a constant independent of the agglomerate size, it has been shown that the agglomerates composed of natural kaolinite particles were better represented by a variable fractal dimension. [49][50][51] Such variable fractal dimension would further complicate the estimate for agglomerate density.…”