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

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) over bar = 160 mu m. 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.