(375d) Investigation of Particle-Size Dependent Charging

Investigation
of Particle-Size Dependent Charging

X. Liu¹,
I. Nwogbaga¹, P. Saba², J. Kolehmainen¹, A. Ozel³, T. Shinbrot⁴,
S. Sundaresan¹

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

²Department of Mechanical and Aerospace Engineering,
Rutgers University, Piscataway, New Jersey 08854, USA

³School of Engineering and Physical Sciences,
Heriot-Watt University, Edinburgh EH14 4AS, UK

⁴Department
of Biomedical Engineering, Rutgers University, Piscataway, New Jersey 08854,
USA

Granular particles tend to develop static charges due
to contacts with walls and other particles in transport lines and fluidized
beds [1]. These systems often operate with various degrees of particle size distributions.
Particles of different sizes of otherwise identical material have been found to
charge differently [2]. Different trends were observed in literature, with some
studies reporting bigger particles tend to charge positively while smaller
particles charge negatively [2,3], as others found the opposite trend [4], but
the phenomenon remains poorly understood [1]. In this study, we seek to
investigate this effect of particle size on tribocharging.

We first conduct vibrated bed experiments with soda
lime glass particles of different sizes in polycarbonate and acrylic containers
of different sizes. In each experiment, particles of one chosen narrow size
range and one mass loading were shaken for a long time in a container in a dry
nitrogen environment and the particle charge was then measured using a Faraday
cup. A Discrete-element-method (DEM) simulation [6] complemented each
experiment in order to determine the effective work function difference between
the particles and container wall that would yield the same level of charge. In
this manner, we probe whether the effective function of a particle relative to
the wall manifested any systematic dependence on particle size.

Additional vibrated bed experiments are performed
using containers whose walls are coated with particles of one size range.
Complementary DEM simulations allowed us to probe directly the differences in
effective work function difference between particles of different sizes.

The results of these
experiments and analyses will be described in this presentation.

[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] 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.

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

[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] Kolehmainen, J.,
Sippola, P., Raitanen, O., Ozel, A., Boyce, C. M., Saarenrinne, P., Sundaresan,
S. Effect of humidity on triboelectric charging in a vertically vibrated
granular bed: Experiments and modeling. Chem.
Eng. Sci. 2017; 173: 363-373.