High-velocity gas flow domination over liquid flow driven by a commercial plasma jet

Plasma-induced liquid flows are thought to be a useful method in controlling the transport and distribution of reactive species through a liquid during plasma–liquid interactions. Using particle image velocimetry, we quantitatively investigate the liquid flow induced by a commercial atmospheric pressure plasma jet, an Argon kINPen IND-X. We find that the kINPen-induced liquid flow is dominated by the background neutral gas flow at application-required flow rates. We come to this conclusion by finding that the liquid flow is the same with or without ionization, even as parameters of the plasma and liquids are changed. We expand on this by comparing the flows driven by the kINPen to two other plasma jets that have been used in past liquid flow research, by using experimental data and dimensionless numbers to characterize certain flow phenomena. One of these dimensionless numbers is a newly defined parameter for general use in discerning whether a plasma jet’s background neutral gas flow is fast enough for electro-hydrodynamic forces in the gas phase to become negligible. Through our comparison of the liquid flows driven by the three investigated plasma jets, we demonstrate how to predict which mechanisms are dominant in the fluid mechanics of a plasma–liquid system, by combining experimental data with easy-to-obtain parameters of the system.