In-Flight Interaction of Water, Glycol, and Alcohol Droplets with a Dielectric Barrier Discharge Plasma*

The use of non-thermal plasmas is becoming ubiquitous for many processes such as disinfection of medical equipment, treatment of surfaces, waste-water treatment, and airplane wing de-icing. It is noted that in most of the aforementioned uses of plasmas there is interaction with droplets of water or other liquids commonly used in these processes, namely alcohols and glycols.

As the initially spherical droplets traverse through a plasma region, chemical, thermal, and mechanical processes take place. The exchange of ions between the gas and liquid phases chemically changes the composition of the liquid.  In particular, the surface tension decreases. This, combined with the body force by the electric field, results in the deformation of the droplet. Departure from sphericity results in increased drag, increased surface-to-volume ratio, and enhanced heat transfer. The degree of droplet deformation is likely to be affected by residence time, intensity of the plasma, droplet size, and the natural frequency of the droplet.

Here, we experimentally show the modes of deformation of water, glycol, methanol, and isopropanol droplets exposed to plasma. Results are presented in relation to the physical properties of the liquids as well as their interaction with plasma streamers.