Post-corona unipolar chargers with tuneable aerosol size-charge relations: Parameters affecting ion dispersion and particle trajectories for charger designs

International audienceThis paper focusses on the mean charge per particle of monodisperse submicron aerosol, charged by diffusion of unipolar ions in post-corona discharge. It aims to confirm and discuss the limits of considering a single value of Ni·t to describe aerosol charging and then to present methods to control the size-charge relation. Three aerosol chargers, with different mixings of ion and aerosol flows are investigated. Despite comparable ion sources with discharge currents of a few tens of µA, the size-charge relations differs from one charger to another due to different ion-aerosol mixing conditions and subsequent ion density along particles trajectories. Discrepancies are even more noticeable as the particle size increases. Discharge current, velocities of ion and aerosol flows and electric field control post-discharge ion density in each point of the charging volume. The control of particle trajectory in expanding unipolar ion cloud, leads to tuneable size-charge relations. Aerosol inertia and charging dynamics, that both depends on particle size, affects the Ni·t experienced by the particle and thus the final charge of the particle. Operating conditions to reach a constant mean charge for particles larger than 200 nm are reported. Conclusions provide a basis to design aerosol chargers devoted to electric mobility selection for aerosol deposition, separation or electrical measurements especially to overcome the limits of mobility-to-size data inversion due to multiple charge ambiguity using diffusion chargers

Ion current density profiles in negative corona gaps versus EHD confinements

International audienceThis paper deals with the electric and hydrodynamic confinement of negative ions in a point-to-plane corona discharge gap. Radial ion current density profiles have been measured on the earthed planar electrode, drilled in the axis of the point. The experimental setup is first validated by comparison with the Warburg's law without injected gas flow rate. The gas injected in the gap and blown from the discharge gap through the hole located at the centre of the plane affects neither the electric field close to the point nor the subsequent electric wind. However, it leads to the confinement of ions flux towards the central symmetry axis in the low electric field region up to a critical gas velocity, which for no more effect is measurable. Hence, electro hydro-dynamics confinement of ions can be achieved by limiting the outward radial expansion of ions to increase ion current densities on specific locations close to the low field planar electrode. © 2015 Elsevier B.V