(663d) Tribocharging of Bidisperse Particles in Fluidized Beds

Tribocharging
of Bidisperse Particles in Fluidized Beds

X. Liu¹,
J. Kolehmainen¹, A. Ozel²,
S. Sundaresan¹

¹Department of Chemical and Biological Engineering,
Princeton University, Princeton, New Jersey 08540, USA

²School of
Engineering and Physical Sciences, Heriot-Watt University, Edinburgh EH14 4AS,
UK

Tribocharging refers to the phenomenon that materials
pick up static charges upon contact with other materials [1]. In fluidized
beds, granular particles undergo tribocharging due to repeated particle-wall
and particle-particle collisions, resulting in complex charge distributions.
Particle size distribution brings in additional complexities [2-4]. In this
study, we seek to investigate the effect of particle size distribution on
tribocharging in fluidized beds by using a bidisperse system as a model
problem.

The system is simulated using Computational Fluid
Dynamics coupled with Discrete Element Method (CFD-DEM) where the tribocharging
model is coupled with hydrodynamics [5]. The rate of charge transfer between
two surfaces that come into contact depends on the effective work function
difference between the surfaces and the local electric field [6]. We first
assign different combinations of effective work functions to the two particle
sizes and vary their size and volume ratio. The relation between these factors
and the resultant charge distribution is examined.

We then simulate the system by assigning the same
effective work function to both particle sizes. When the effective work
function of the wall is different from that of the particles, a
counter-intuitive bipolar charge distribution is found to develop. The source
of opposite charges in the system is investigated based on the macroscopic
electric field and particle-particle and particle-wall collisions.

[1]
Lacks, D., Mohan, S. Contact electrification of insulating materials. J. Appl. Phys. 2011; 44(45).

[2] Forward, M., Lacks,
D., Mohan, S. Charge Segregation Depends on Particle Size in Triboelectrically
Charged Granular Materials. Phys. Rev. Lett 2009; 102(2): 028001.

[3] Schella, A., Weis,
S., Schröter, M. Charging changes contact composition in binary sphere
packings.  Phys. Rev. E 2017;
95(6): 062903.

[4] Lee, V., Waitukaitis, S., Miskin, M., Jaeger, H. Direct
observation of particle interactions and clustering in charged granular
streams. Nat. Phys. 2015; 11: 733–737.

[5] Kolehmainen, J., Ozel,
A., Boyce, C. M., Sundaresan, S. Triboelectric charging of monodisperse
particles in fluidized beds. AIChE J 2017; 63(6): 1872–1891.

[6] Laurentie, J. C., Traoré,
P., Dascalescu, L. Discrete element modeling of triboelectric charging of
insulating materials in vibrated granular beds. J Electrostat 2013; 71(6): 951-957.