Measurements of equilibrium charge distribution on aerosols in bipolar ionic atmosphere

Enhanced attraction between drops carrying fluctuating charge distributions

The electrostatic force between conductive spheres is always attractive at small separations, irrespective of their mean charge, when the charge on the spheres is constant. In many situations, the charge may not be fixed, such as for water drops in the natural atmosphere which vary in size and charge. We show that the attractive force between charged conductive spheres increases with increasing charge variance. The importance of this unrecognized electrostatic effect between water drops is evaluated for its potential to enhance rain formation.

Time-lapse visualization of shrinking soot in diesel particulate filter during active-regeneration using field emission scanning electron microscopy

Regeneration of diesel particulate filter (DPF) is a complicated process due to its high operating temperature and associated oxidation of soot on the filter substrate. Several oxidation mechanisms of diesel soot have been proposed based on reaction kinetics, but more information about the oxidation phenomena is needed in a practical system, that is, soot oxidation on a DPF substrate. In this work, the DPF regeneration process was, for the first time, visualized at the particle scale ex-situ, in time-lapse series, using field emission scanning electron microscopy (FE-SEM). Time-lapse transformation of soot cake layer on a real DPF was followed from initiation through the complete regeneration process. In parallel, transformation of the soot primary particle diameter was directly measured using high-resolution transmission electron microscopy. FE-SEM visualization clearly showed shrinkage of the soot cake layer on the DPF wall as oxidation progressed. Furthermore, diameter distribution analysis revealed a trend of shrinkage of the nanoscale soot primary particles during oxidation, supporting the FE-SEM observations of the micron-scale shrinkage of the agglomerated soot cake layer. Fragmentation of the shrunken soot cake layer was also observed and is suspected to be a result of locally higher gas flow that depends on surface pore morphology of the filter substrate. LAY DESCRIPTION: In this work, the DPF regeneration process was, for the first time, visualized at the particle scale ex-situ, in time-lapse series, using field emission scanning electron microscopy (FE-SEM). Time-lapse transformation of soot cake layer on a real DPF was followed from initiation through the complete regeneration process. In parallel, transformation of the soot primary particle diameter was directly measured using high resolution transmission electron microscopy. FE-SEM visualization clearly showed shrinkage of the soot cake layer on the DPF wall as oxidation progressed. Furthermore, diameter distribution analysis revealed a trend of shrinkage of the nano-scaled soot primary particles during oxidation, supporting the FE-SEM observations of the shrinkage of the micron-scale agglomerated soot cake layer. Fragmentation of the shrunken soot cake layer was also observed and is suspected to be a result of locally higher gas flow that depends on surface pore morphology of the filter substrate. Further detail mechanism about transformations of the soot cake layer was additionally discussed based on electrostatic attraction.