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

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. (C) 2020 Chinese Society of Particuology and Institute of Process Engineering, Chinese Academy of Sciences. Published by Elsevier B.V. All rights reserved.

Automated summary

In gas-solid fluidized beds, particle-particle and particle-wall collisions cause charge accumulation on particles. This study evaluated the impact of fluidization time on charge transfer and bipolar charging, and their effects on hydrodynamic structures in a fluidized bed. The results show that bipolar charging is the dominant mechanism in a bed of glass beads, while the difference in work functions between wall and particle leads to high charge transfer in a bed of polyethylene particles.