Impact of Water PH on Liquid Phase Plasma Initiation

Multiphysics simulations are performed to identify the role of water pH level on liquid phase plasma discharge formation. The simulations are conducted for a needle-like powered electrode with an exponential nanosecond rise time. The simulations indicate that water pH level that denotes the available negative hydroxyl ions (OH - ) in the liquid phase has a strong influence on the discharge initiation. Electron detachment from OH - requires a much lower threshold energy and therefore provides a stream of electrons during the initial stage. A higher pH (i.e., alkaline water) allows the initial stream of electrons to be present at higher concentration and propagates further downstream from the powered electrode. The resulting electrical forces at higher pH level create larger density variation in the liquid and a significantly higher bulk fluid velocity is observed. The electron detachment from the OH - is not limited by the available electric field strength, rather the availability of negative hydroxyl ions in the system and ceases when these ions are depleted. Acidic water on the other hand was found to require higher electric field for the breakdown to take place as the system is deprived of critical initial concentration of OH - .