(87c) Effect of Electric Field on the Hydrodynamics of Nanoparticles in a Rectangular Fluidized Bed

Nanoparticles have unique flow properties that make them useful for numerous applications. Several publications [Zhu et al. (2005), Jung & Gidaspow (2002), Huang et al. (2006)] have recently demonstrated that silica nanoparticles can be fluidized without the formation of bubbles. This property eliminates the major disadvantage of fluidized beds, formation of large bubbles that cause gas bypassing and hence poor reaction.

The effect of electric field on 10 nm silica particles was studied in a specially designed rectangular fluidized bed having an internal cross section of 4.5 in. x 5.5 in., with electrodes attached to two parallel walls. Experiments were conducted using various combinations of superficial gas velocities and electric field strengths.

The bed height decreased drastically on the application of electric field. The decrease was almost linear at 0.70 kV/cm. It was non-linear and larger at 1.05 kV/cm and 1.40 kV/cm. These observations were reverse of those obtained earlier [Wittmann & Ademoyega (1987)] with 177-210 micrometer silica gel particles. The average size of the agglomerates was calculated at various electric fields, using the Richardson-Zaki equation. The size increased from 204 μm to 396 μm when the electric field was increased from 0 kV/cm to 1.40 kV/cm.

Particle density profiles were also determined as a function of solids volume fraction and bed height at different electric fields. These data allowed the computation of granular temperatures using a one dimensional particle momentum balance with the ideal equation of state [Driscoll & Gidaspow (2006)]. This balance is similar to a barometric formula for gases. The granular temperature decreased with the increase in electric field.

References:

1. Chao Zhu, Qun Yu, Rajesh N. Dave & Robert Pfeffer, 2005. Gas Fluidization of Nanoparticle Agglomerates. AIChE Journal. 51: 426-439

2. Jonghwun Jung & Dimitri Gidaspow. Fluidization of nano-size particles. Journal of Nanoparticle Research 4: 483-497, 2002

3. Cang Huang, Yao Wang & Fei Wei, 2006. Multi-Stage Agglomerate Structure and Solids Mixing Behavior of Nano-Particle in Fluidized Bed. 5th World Congress on Particle Technology, Orlando, 2006

4. Charles V. Wittmann & Benjamin O. Ademoyega. Hydrodynamic Changes and Chemical Reaction in a Transparent Two-Dimensional Cross-Flow Electrofluidized Bed. 1. Experimental Results. Ind. Eng. Chem. Res. 1987, 26, 1586-1593

5. Michael Driscoll & Dimitri Gidaspow. Wave Propagation and Granular Temperature in Fluidized Beds of Nano and Fcc Particles. AIChE Annual Meeting, San Francisco, 2006