Corona discharge in electrospraying

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

“…-Measurements of the mean current versus flowrate and conductivities for comparison to scaling laws established for the cone-jet (see 3.2 and 3.3.1.4). For unsteady ES modes, oscilloscope measurements of currents are useful to define the droplet emission frequency of dripping or spindle modes, and even critical to deal with ES destabilization by transient discharges such as pre-onset streamers, streamers and sparks (Borra et al, 1996;Borra et al, 1999d;Ehouarn P. et al, 2001;Borra et al, 2004;Pongrác et al, 2014;Verdoold et al, 2014;Pongrác et al, 2016), as first reported on pending drops (see introduction) and confirmed by emission spectroscopy (Meesters et al, 1992;Jaworek et al, 2014). -Droplets properties (size distributions, charge per drop) and spray expansion (2D velocities, fluxes and concentration profiles) evaluated from Laser Phase Doppler measurements at different radial positions from the symmetry axis of nozzle, cone, jet and spray, versus voltage, flow rate and conductivity (Cloupeau et al, 1989;Snarski et al, 1991;Dunn et al, 1992;Tang K et al, 1994bTang K et al, , 1995Grace et al, 1996;Hartmann et al, 1996;Naqwi et al, 1996;Tang K et al, 1996;De Juan et al, 1997;Gañán-Calvo et al, 1997;Olumee et al, 1998;Hartmann et al, 1999a;Ku et al, 2002;Wilhelm et al, 2006).…”

“…In that case, the steady cone-jet mode cannot be induced, as reported over huge ranges of conductivities (from a fraction of mS.m -1 for de-ionized water to S.m -1 for biological aqueous samples up to a few S.m -1 for sea water) and flowrates (from nL.min -1 to tens mL.min -1 ) in air, (Juraschek et al, 1998;Sugimoto et al, 2001;Kawamoto et al, 2005;Bruggeman et al, 2007;Shirai et al, 2011;Sun et al, 2011;Shirai et al, 2014;Higashiyama et al, 2017;Xu P et al, 2017). All these modes, other than the steady cone-jet, lead to droplets emission from the capillary or/and from the jet in dripping, micro-dripping, spindle, intermittent cone-jet, precession and (multi)-jetting modes reported, at increasing flowrate, (Smith, 1986;Hayati et al, 1987b;Bailey, 1988;Cloupeau et al, 1994;Tang K et al, 1995;Borra et al, 1996;Jaworek et al, 1997;Ehouarn P. et al, 1999; 2005; Pongrac et al, 2011;Jaworek et al, 2014;Kim HH et al, 2014;Pongrác et al, 2014;Pongrác et al, 2016). These modes, other than the steady corona-assisted cone-jet are here gathered under the generic expression "unsteady ES modes" even if by essence, droplet emission occurs with repetitive cycles of a necessarily unsteady liquid fragmentation zone.…”

“…Since Zeleny's observations of electrical discharges from water drop, ES in cone-jet was reported as destabilized or prevented by discharges (Zeleny, 1917;English, 1948;Hayati et al, 1987b;Bailey, 1988). Then, "a stabilized ES mode by the pulseless corona" has been described (Cloupeau et al, 1989(Cloupeau et al, , 1990, confirmed in CO 2 (Tang K et al, 1994b(Tang K et al, , 1995 and air (Borra et al, 1996;Jaworek et al, 1997;Borra et al, 1999d;Ehouarn P. et al, 1999;Borra et al, 2004;Lopez-Herrera et al, 2004;Jaworek et al, 2014). Without discharges, ES works in both + and -DC as well as in AC polarities, as mentioned in the introduction to account for water ES from HV power lines.…”

Investigation of the Corona Discharge Problem Based on Different Computational Approaches of Dimensional Analysis

“…However, the electric field distributions on the corona electrode surface were slightly different. The current-voltage and light emission characteristics of electrospraying of various liquids in standard atmospheric air were investigated in [10]. The spectroscopic measurements reveal that the onset of corona discharge coincides with the beginning of electrospraying where the dependence of the amplitude of selected spectral lines on capillarynozzle voltage was determined from the measured light emission spectra of discharges from the capillary nozzle and liquid jet.…”

“…However, Chattok [9] was the first to analyze this phenomenon quantitatively. Corona discharges from the surface of a conducting liquid, which might comprise liquid jets from electrospray nozzles or charged droplets, were also explored a variety of perspectives, including those of current-voltage characteristics, recording of current waveforms, steady or streak photography, mass spectrometry, light intensity measurements, and optical emission spectroscopy [10].…”