Induction of Waves on a Horizontal Water Film by an Impinging Corona Wind

The electric wind produced by corona discharge of a high-voltage electrode in air is employed for destabilizing a horizontal water film. In wire-to-plane geometry, the phenomenon is characterised by current-versus-voltage curves and visual observations of the onset of free surface oscillations. The effect of the following parameters is examined: distance between the wire and the film (d), film thickness (h), wire diameter (φ) and composition, polarity of the applied voltage (HV). The free surface destabilisation is retarded by increasing d and φ and is insensitive to h. The onset of corona discharge is predicted by Peek’s law and compared with the experimental data. In positive corona discharge, the increase in HV is limited by the electrical breakdown of air, while, in negative polarity, the corona current reaches a saturation at about 5 μA. The delay, in terms of HV, between the onset of the corona discharge and the beginning of the film destabilisation is smaller for the negative electric wind, which seems to blow stronger than the positive one. The energy loss by corona discharge is lower than 0.15 W. Wave induction on the liquid-gas interface can effectively improve heat and mass exchange between the two phases.