Charge transfer and bipolar charging of particles in a bubbling fluidized bed--颗粒学报PARTICUOLOGY

Manafi, M., Zarghami, R., & Mostoufi, N. (2021). Charge transfer and bipolar charging of particles in a bubbling fluidized bed. Particuology, 54, 109-115. https://doi.org/10.1016/j.partic.2020.02.008

Charge transfer and bipolar charging of particles in a bubbling fluidized bed

Mahshad Manafi, Reza Zarghami ^*, Navid Mostoufi

Multiphase Systems Research Laboratory, School of Chemical Engineering, College of Engineering, University of Tehran, P.O. Box 11155-4563, Tehran, Iran

10.1016/j.partic.2020.02.008

Volume 54, February 2021, Pages 109-115

Received 9 October 2019, Revised 10 February 2020, Accepted 18 February 2020, Available online 23 May 2020, Version of Record 28 January 2021.

E-mail: rzarghami@ut.ac.ir

Highlights

• Bipolar charging does not noticeably affect fluidization structures.

• Charge transfer results in opposite charges on the wall and polyethylene particles.

• Charge transfer during fluidization causes a stagnant layer to form on the wall.

• The energy of macro-structures initially increases owing to formation of the layer.

• Repulsion between particles with the same polarity causes bubble size to decline.

Abstract

Particle–particle and particle–wall collisions in gas–solid fluidized beds lead to charge accumulation on particles. This work evaluated the effect of fluidization time on charge transfer and bipolar charging (charge separation) and their influence on hydrodynamic structures in a fluidized bed. Experiments were performed with glass beads and polyethylene particles in a glass column. The pressure fluctuations and net electrostatic charge of particles were measured during fluidization. Wavelet and short-time Fourier transforms were used to analyze pressure fluctuations. The results revealed that bipolar charging is the dominant tribocharging mechanism in a bed of glass beads. Bipolar charging in a bed of particles with a narrow size distribution does not affect either hydrodynamic structures or the transition velocity to the turbulent regime. A large difference between the work functions of the wall and particle in the bed of polyethylene particles leads to high charge transfer. Formation of a stagnant particle layer on the wall eventually causes the energy of macro-structures to increase to its maximum. At longer fluidization times, the macro-structural energy decreases and bubbles shrink until the electrostatic charge reaches the equilibrium level. These results well describe the effect of fluidization time on hydrodynamic structures.

Graphical abstract

Keywords

Contact; electrification; Charge transfer; Bipolar charging; Pressure fluctuations; Fluidization structures

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