Electrification of saltating particles in wind‐blown sand: Experiment and theory

Abstract

[1] The electrification of sand particles is a common phenomenon in wind-blown sand movement. The charge-to-mass ratio of particles is an important parameter to characterize the property of charged particles. However, understanding of the charge-to-mass ratio remains open, and significant discrepancies exist between previous contact electrification models and measurements. This work focuses on the charge-to-mass ratio of saltating particles in wind-blown sand. Experiments were carried out in a wind tunnel using sand particles with the mean diameter d ¼ 160 μm. The motions of the saltating particles in the air flow were analyzed by particle image velocimetry, and the charge-to-mass ratios were determined by measuring both the charge and mass of saltating sand particles collected in a Faraday cup. The measured results show that the charge-to-mass ratio increases exponentially with the height above the surface and the vertical profiles of the charge-to-mass ratios can be reproduced well by considering the multiple collisions process between saltating particles and sand bed. In addition, the results suggest that the charge-to-mass ratio is determined by the number of collisions, impacting velocity, and sand grain diameter combined.Citation: Zhang, H., X.-J. Zheng, and T. Bo (2013), Electrification of saltating particles in wind-blown sand: Experiment and theory,

Dust devil dynamics

“…We use simple parameterizations from the Lacks and Levandowsky [2007] experiments in our hydrodynamic model to calculate the amount of sand and mineral dust raised in a dust devil. The explicit use of hydrodynamics may add confidence in the meteorology communities' ability to estimate and forecast the amount of material in the atmosphere to be used in global circulation models of the troposphere [Schmidt et al, 1998;Zhang et al, 2003;Arnas et al, 2013]. From the particle charge distribution versus particle radius distribution shown in Lacks and Levandowsky [2007], we can estimate the vertical electric field from the stratification of the particles.…”

Quantifying the large-scale electrification equilibrium effects in dust storms using field observations at Qingtu Lake Observatory

“…In addition to affecting dust transport, the E-fields created by charged dust may contribute to detection and early warning of severe dust events. For example, Aizawa et al (2016) and Zhang et al (2017) have documented that the substantial enhancement in the inten-H. Zhang and X. Zheng: Quantifying the large-scale electrification equilibrium effects sity of E-field occurs prior to the arrival of the dust clouds (fronts). Therefore, there is the considerable impetus to investigate electrical effects in dust events.…”

“…Previous studies are mainly concerned with the vertical profile of E-fields in the near-ground region and their influence on dust transport (e.g., Kamra, 1972;Rudge, 1913;Yair et al, 2016). The measurements showed that the vertical E-fields decrease with increasing height in the sub-meter region (e.g., Schmidt et al, 1998), but exhibit multi-layer properties in the region of up to 30 m height (Zhang et al, 2017). Though measurements of E-fields in dust events are numerous, the measurements associated with the electrical properties of dust particles are relatively sparse.…”

“…Furthermore, a large number of theoretical works and laboratory experiments have shown that the net electrical charge on millimeter-sized particles increases with increasing number of collisions/contacts and correlates with the particles' kinetic energy (Apodaca et al, 2010;Harper and Dufek, 2016;Matsuyama and Yamamoto, 1995;Zhang et al, 2013) until particles acquired a certain amount of charge (termed as equilibrium charge). The magnitude of the eventual equilibrium charge on particles is found to be independent of the particles' collisional dynamics and therefore will reduce the difficulties in the quantification of particle electrification.…”

“…However, whether such an electrification equilibrium exists under natural circumstances, especially for micron-sized dust particles in dust storms, is unclear and needs to be verified. Additionally, preliminary research (Esposito et al, 2016;Merrison, 2012;Xie and Han, 2012;Zhang et al, 2017;Zheng et al, 2014) suggests that environmental factors such as the ambient temperature and RH could considerably affect the intensity of E-fields. It is still unknown whether environmental factors have an impact on the properties of dust electrification, and especially electrification equilibrium effects in a dust storm.…”