Review on water electro-sprays and applications of charged drops with focus on the corona-assisted cone-jet mode for High Efficiency Air Filtration by wet electro-scrubbing of aerosols

Jean-Pascal Borra (1)

1 LPGP - Laboratoire de physique des gaz et des plasmas

Highlights:  electrosprays is a continuous production process of self-dispersed unipolar droplets with monodisperse/unimodal size distributions (0.2 < d modal < 150 µm)  Applications of ES of aqueous solutions are reviewed with special attention for material production and bio-applications  Means to achieve steady water ES are presented with respect to electrical discharges in ambient air around the liquid cone and jet  Streamer discharges with transient and asymmetric space charges disrupt the EHD equilibrium for steady cone-jet mode, while the axisymmetric and quasi-stationary space charge is required to achieve steady water ES in the pulseless corona-assisted cone-jet mode  Empirical scaling laws of droplet properties are reminded for both steady water ES in cone-jet with a pulseless corona and without discharge  High filtration efficiencies of a lab-scale wet bipolar-scrubbers (>99%) supports that Water ES in corona-assisted cone-jet could be applied to low cost Air cleaning Abstract: Electrospray of Water and aqueous solutions is a simple, steady and continuous process for the production of charged droplets. Applications of this low cost spraying process, easy to scale up and environment friendly with low water consumption are first presented. This review addresses the Electro-Spray (ES) in the cone-jet mode, with focus on water ES with or without discharges in ambient air. The physical constraints to achieve steady water electrospray in ambient air are depicted to account for Electro-Hydro-Dynamic equilibrium required for the cone and jet formation on the one hand and to control electrical discharges in the gas around the liquid (with continuous corona or without any discharge) on the other hand. Operating conditions and empirical scaling laws between regulation parameters (liquid flow rate and corona current) and the properties of droplets such as the size and the charge are presented for the corona-assisted cone-jet mode of water electrospray in air. Subsequent working conditions to achieve the other steady water ES, without discharge, are then justified. The interest of this corona assisted cone-jet mode of electrospray in air for the steady production of self-dispersed unipolar water droplets (close to the Rayleigh limit) with unimodal size distribution is presented with one environmental application for filtration by bipolar-scrubbing of suspended particles from exhaust or ambient aerosols, with lab-scale efficiencies of High Efficiency Particulate Air filters.

Mots clés: Water; Electrospray; EHD; electrical discharges; corona; wet scrubbing

Domaines: Sciences de l'ingénieur [physics]; Génie des procédés; Plasmas; Ingénierie de l'environnement

Jean-Pascal Borra. Review on water electro-sprays and applications of charged drops with focus on the corona-assisted cone-jet mode for High Efficiency Air Filtration by wet electro-scrubbing of aerosols. Journal of Aerosol Science, 2018, 125, pp.208-236. ⟨10.1016/j.jaerosci.2018.04.005⟩. ⟨hal-02415646⟩