Akademik Veri Yönetim Sistemi
American Vacuum Society (AVS) 68th International Symposium & Exhibition, Ohio, Amerika Birleşik Devletleri, 6 - 11 Kasım 2022, (Özet Bildiri)
Plasmas in contact with liquids are of interest because of the complex interactions and potential for novel physical and chemical processes. In general, the system is composed of the gas-phase, liquid-phase, and the gas-liquid interface. Experimental measurements have been made in the gas phase and liquid phase of a plasma-liquid process, and more recently modeling has also been performed. There remains a need to compare experiments and modeling to validate simulation outputs and develop predictive capabilities.
This talk will focus on two important aspects plasma-liquid processes: predicting the species densities and heat transfer phenomena near the interface. The focus of our study was a direct-current (DC) operated pin-to-plane electrode geometry with the liquid serving as an electrolyte and a counter electrode immersed in the solution. First, our recent studies on developing a one-dimensional, isothermal but unsteady-state model for coupled plasma-liquid interactions will be presented1. Using a drift-diffusion-reaction formalism, plasma and aqueous chemistry was solved for in an argon-salt water system. In this system, one of the reactions that occurs is the formation of hydroxyl radicals, which subsequently produce hydrogen peroxide. We studied potential mechanisms for hydrogen peroxide production with the plasma operated as either the cathode or anode. Experiments were performed in support of modeling to characterize the plasma and measure the aqueous hydrogen peroxide, and both modeling and experimental results show that its production is substantially higher during anodic operation. Most importantly, the model can successfully predict the order of magnitude of H2O2 generation rate in the bulk liquid during anodic operation.
In the second part of this talk, it will be shown that a major portion of the energy in the pin-to-plane electrode is dissipated as heat during cathodic operation. Optical emission spectroscopy indicates that even for a discharge power of less than 2 W, the gas temperature may surpass 1000 K in the cathode sheath, which subsequently heats up the electrode. For small electrode geometries, cathode heating is visible due to extensive blackbody radiation, which confirms the gas temperatures measured by spectroscopy. Despite being only 1 mm away from the cathode, infrared thermometry indicates that the water interface remains surprisingly cool, reaching a maximum of only 335 K. These findings suggest that in addition to the inherent local non-equilibrium between the electrons and larger species in the plasma, there exists a very strong thermal non-equilibrium across the plasma as well.