The effect of gravity direction on the EHD surface waves of dielectric oil thin films generated by wire-plate barrier discharges

An experimental investigation has been conducted to study the effect of gravity direction on the EHD (electrohydrodynamically) induced surface wave phenomena on the surface of dielectric diesel oil thin films under wire-plate barrier discharges. Diesel oil used is dielectric constant ε_s=2.2 and conductivity σ=5×10^-5 μS/m and positive dc (on/off) high voltage was imposed on the plate electrode. Experiments are conducted for the applied voltage from 0 to 29 kV and gravity to corona wire (horizontal electric field) direction from (co-field) to 90 (cross-field) degrees. The experimental results show that: (1) The oil film wire and an expanding depression surface wave initiated with short time delay when voltage is off to on under cross-field cases. After another short delay, hydraulic jump imploding wave is also generated. (2) For voltage on to off in cross-field case, T-L type expanding wave is generated with short delay time and then imploding wave is formed behind T-L type waves. (3) For the co-field case, expanding wave without imploding wave formation in voltage off to one conditions was observed, and T-L type wave with imploding wave was observed in on to off conditions. The wave propagation speed is always higher in the gravitation direction