The electrification of sand particles plays an important role in aeolian events. In this paper, the charge-to-mass ratio vertical profiles of saltating particles in wind-blown sand were measured by a field experiments. By combining the results of field measurements with our previous wind-tunnel measurements, we discussed the factors affecting the charge-to-mass ratio of saltating particles. It reveals that the magnitude of the charge-to-mass ratio increases exponentially with height above the surface. In addition, the charge polarity of saltating particles depends on the relative size between saltating and creeping particles, and the magnitude of charge-to-mass ratio is determined by wind velocity and the relative size difference ratio between saltating and creeping particles.
While the electrification of dust storms is known to substantially affect the lifting and transport of dust particles, the electrical structure of dust storms and its underlying charge separation mechanisms are largely unclear. Here we present an inversion method, which is based on the Tikhonov regularization for inverting the electric field data collected in a near-ground observation array, to reconstruct the space-charge density and electric field in dust storms. After verifying the stability, robustness, and accuracy of the inversion procedure, we find that the reconstructed space-charge density exhibits a universal three-dimensional mosaic pattern of oppositely charged regions, probably due to the charge separation by turbulence. Furthermore, there are significant linear relationships between the reconstructed space-charge densities and measured PM10 dust concentrations at each measurement point, suggesting a multi-point large-scale charge equilibrium phenomenon in dust storms. These findings refine our understanding of charge separation mechanisms and particle transport in dust storms.
[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,
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