Computational studies of plasma–liquid interactions
2020-05-28T11:12:55Z (GMT) by
By the introduction of modern power supplies capable of producing low-temperature plasma under atmospheric pressure, the interaction between plasmas and liquids have presented great potentials in many exciting applications in recent years. Cancer treatment, wound healing, nanomaterial production, water disinfection and chemical analysis are just a few examples of emerging applications of plasmas interacting with liquids.
Despite the large attention received in recent years, research in this area is still in its infancy. To take the current technologies further and develop practical solutions for these applications, many fundamental questions need to be answered first. Although reactive oxygen species (ROS) and reactive nitrogen species (RNS) are known to play a dominant role in these applications. The underlying physics of plasma-liquid interaction, the chemistry involved in the liquid phase, the interfacial effects governing the mass transfer between the plasma and the liquid, mass transfer quantities and the propagation mechanisms of the transferred species throughout the liquid media are just a few sample questions that remain unanswered.
A combination of computational modelling and experimental methods are used throughout this thesis to shine some light on some of these questions. New insights into the dynamics of the liquid phase chemistry as well as the physical effects of the plasma on the liquid bulk are addressed as part of this thesis. The developed computational model not only provides a better understanding of the system in general, but also predicts properties and quantities which are difficult or impossible to measure experimentally with current available apparatus and measurement techniques. The results are then employed to layout guidelines for optimized configurations of plasma-liquid systems in practical applications.
Since the gas phase computational study has been explored extensively in previous works, in this thesis our main focus will be the interaction between the plasma and the plasma effluent with the liquid phase and the subsequent physicochemical reactions.
The problem is broken down into three parts. In the first part, the plasma gas phase is studied independent of the liquid phase to clarify the kinetics of the plasma medium. The main chemical reaction pathways are studied as well as the effect of input power modulation on the chemical pathway variations and final gas composition.
The next part focuses on the transfer of heavy reactive species into the liquid and the subsequent chemical reactions. This is relevant in remote plasma systems in which the plasma is not in electric contact with the liquid. In particular we study an epoxidation reactor that relies on a He + O2 to epoxidate alkenes in liquid phase.
In the third part, the focus is on the transfer of electrons into the liquid phase. In this case, the plasma is electrically connected to the liquid and electrons are delivered to the liquid to drive liquid phase reactions. The electrochemical properties of the liquid are studied along with the effect of the surface tension gradient caused by the plasma on the liquid phase mixing patterns.