Study of DC and Pulsed Corona Discharges in Gases, Vapors and Liquids for Phase-Change Heat Transfer Applications
Abstract
A plasma can produce highly energetic and chemically active species making it attractive for industrial applications. In this work we investigate both, the DC negative plasma discharges at lower discharge currents (0-0.8 mA), and a negative pulsed corona discharge. DC plasma discharges in a pin-to-plate electrode configuration were electrically, optically and spatially characterized for various plate electrodes (anodes): solids as well as liquids. The negative corona discharge regime and a non-stationary filamentary glow discharge regime were observed with an additional intermediate streamer-spark discharge regime depending on the surface roughness and the discharge gap for solid anodes. The negative corona discharge regime was observed to have a conical diffuse glow region close to the anode for solid and polar liquid anodes.
Solid anodes surface treated in this negative corona discharge regime (with a diffuse glow) were observed to have a change in wettability and an increase in roughness. Imaging revealed the formation of micro/nanostructures with poor adhesion to substrates of Au, Pt and Si. X-ray photoelectron spectroscopy measurements revealed oxidation of the anode materials. Unlike Au, Pt and Si, thin metals films of Al, Cu and Ni were damaged potentially due to a moving constriction within the diffuse glow region. We hypothesize that this constriction likely oxidized the anode surface resulting in metal oxides that do not adhere well to their parent metals. Further research is required to understand the local surface chemistry within the diffuse glow.
A double spark gap pulse generator was built and used to generate nano-to-microsecond pulsed corona discharges in air, and fluid vapor and liquid phases. The circuit was characterized for the magnitude of the pulse discharge voltage and pulse duration, at atmospheric and sub-atmospheric pressures. This pulsed negative corona discharge may be leveraged to make accurate, local and non-contact measurements in phase change heat transfer processes, both for temperature and species diagnostics.
Citation
Jakhar, Karan (2020). Study of DC and Pulsed Corona Discharges in Gases, Vapors and Liquids for Phase-Change Heat Transfer Applications. Master's thesis, Texas A&M University. Available electronically from https : / /hdl .handle .net /1969 .1 /193026.