Dynamics of a Supercooled Water Droplet During In-Flight Interactions With a Dielectric Barrier Discharge Plasma

Here, we experimentally investigate the dynamic behavior of single supercooled droplets falling through a volume of DBD plasma. To achieve a supercooled state, droplets of deionized water are freely suspended by means of an acoustic levitator in a low temperature enclosure. The levitator is placed over a DBD plasma reactor. The reactor is comprised of two electrode disks which planar faces are parallel to each other. One of the electrodes is supplied with a high-voltage AC sinusoidal signal (25 kVpp and f = 10 kHz) while the other one is grounded. A quartz disk is affixed to each of the electrodes to create the dielectric barrier. When the voltage is applied, a volume of plasma is generated within the spacing between the two quartz plates. Once the droplet in the levitator achieves a supercooled state, it is released to fall through the region of plasma. The droplet trajectory and shape oscillations during its interactions with the plasma are monitored using high-speed imagery. The finding suggest that the shape oscillations are suppressed in the supercool state when falling through no plasma and high intensity plasma discharges (lower electric field). At low plasma intensity (higher electric field) oscillations exist in the supercooled state, but droplet relaxation in the oblate mode is suppressed. The reported data suggested that room temperature droplets oscillate near their natural frequency at all plasma intensities, whereas supercooled droplets (at low plasma intensity) oscillated at nearly half of their natural frequency.