Surface Effects Drive Plasma Induced Liquid Flow in Purified Aqueous Solutions*

Plasma-liquid interactions involve the dosing of charged and reactive species into a typically aqueous solution. The distribution of these species through the liquid is important to optimisation, and the desired distribution varies depending on the application. 

One possible method to control species distribution is through plasma induced liquid flow. Here, the species are pushed and redistributed through the liquid when it moves, therefore leading to a desire for flow control. Unfortunately, there is little understanding of plasma driven fluid mechanics, and a similar lack of literature on the topic. There are numerous possible sources of flow including; electro-hydrodynamics, surface tension gradients, and both normal and shear stresses. These all occur simultaneously and in opposition to one another, and our understanding of them is severely limited.

We have employed particle image velocimetry to non-intrusively and quantitatively observe the flow of de-mineralised water during helium plasma jet impingement, driven by both AC and pulsed power supplies. Our results suggest shear stresses from interfacial ionic drift as the dominant driver of flow in purified water solutions. We back these results up with theory and models, but also describe the gaps in our current description.