The
Effect of Ambient Gas Species on Tribocharging

X. Liu¹,
J. Kolehmainen¹, A. Park², S. Sundaresan¹

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

²Department of Chemical Engineering, Columbia
University, New York, New York 10027, USA

Tribocharging refers to the phenomenon that materials
pick up static charges upon contact with other materials [1]. Ambient gas is
known to limit the maximum charge acquired by tribocharging on a surface through
dielectric breakdown [2-4], but most studies mainly concern tribocharging in air
or nitrogen [2]. In this study, we seek to investigate the effect of ambient
gas species on tribocharging through vibrated bed experiments in nitrogen and
argon.

We first conduct vibrated bed experiments with soda
lime glass particles and polyethylene particles of different sizes in an
acrylic bed. In each experiment, particles of one chosen narrow size range and
one mass loading are shaken for a long time in the container and the total charge
on particles is then measured by a Faraday cup. We conducted these experiments
in dry nitrogen and dry argon and observed that the charge level measured in
nitrogen is higher than that in argon.

We then improve our current charge transfer model used
in discrete element method (DEM) simulation [5-6] by including the effect of
dielectric breakdown. Although the breakdown electric field strength varies
with the separation distance between particles [4], as a simplification, we
only consider dielectric breakdown between contacting particles. We set up
complimentary DEM simulation and found lowering the dielectric breakdown field
strength results in lower charge level. This suggests that the difference in
charge level measured in nitrogen and argon could stem from the differences in
the dielectric field strength.

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

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T., Grace, J. R. Electrostatics in gas-solid fluidized beds: a review. Chem Eng Sci. 2017; 173: 303-334.

[3] Matsuyama, T.,
Yamamoto, H. Charge-relaxation process dominates contact charging of a particle
in atmospheric condition: II. The general model. J Phys D. Appl Phys. 1997;
30(15): 2170.

[4] Matsuyama, T. A
discussion on maximum charge held by a single particle due to gas discharge
limitation. AIP Conf. Proc. 2018;
1927: 020001.

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

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