Jose L. Lopez

A dc non-thermal atmospheric-pressure plasma microjet

A direct current (dc), non-thermal, atmospheric-pressure plasma microjet is generated with helium/oxygen gas mixture as working gas. The electrical property is characterized as a function of the oxygen concentration and show distinctive regions of operation. Side-on images of the jet were taken to analyze the mode of operation as well as the jet length. A self-pulsed mode is observed before the transition of the discharge to normal glow mode. Optical emission spectroscopy is employed from both end-on and side-on along the jet to analyze the reactive species generated in the plasma. Line emissions from atomic oxygen (at 777.4 nm) and helium (at 706.5 nm) were studied with respect to the oxygen volume percentage in the working gas, flow rate and discharge current. Optical emission intensities of Cu and OH are found to depend heavily on the oxygen concentration in the working gas. Ozone concentration measured in a semi-confined zone in front of the plasma jet is found to be from tens to ~120 ppm. The results presented here demonstrate potential pathways for the adjustment and tuning of various plasma parameters such as reactive species selectivity and quantities or even ultraviolet emission intensities manipulation in an atmospheric-pressure non-thermal plasma source. The possibilities of fine tuning these plasma species allows for enhanced applications in health and medical related areas.

Optimization of Large-Scale Ozone Generators

In large-scale ozone generators for industrial or public utilities applications, low-power consumption, robustness of operation, and minimum maintenance requirements are of the highest importance. In order to meet these operational parameters, this paper explores the possibility to use inhomogeneous feed gas processing in a new generation of large-scale ozone generators. We utilize a finite-element model to simulate a discontinuous power induction along the length of the ozone generator tube. The simulation yields the local power density, the local gas temperature gradient, and a relative dielectric barrier discharge (DBD) filamentation packing density. This information, in conjunction with experimental data, provides a sufficiently broad basis of information to infer a correlation between the electrode arrangement and the ozone generation efficiency and overall ozonizer performance. Several ozonizer configurations were designed, simulated, manufactured, tested, and their performance was assessed. This led to a new design for large-scale ozone generators with the possibility of increasing ozone formation efficiency through the tailoring of the DBD microdischarges or microplasmas. The new arrangement tolerates a higher power induction at the inlet of the ozonizer, which has several advantages over constant power induction arrangements. The degree of DBD filamentation emerges as the decisive factor that enables the tailoring of the plasma. Evidence of an increased O3 generation efficiency and significantly reduced electrical power consumption are shown on an industrial-scale ozonizer with more than 100 m2 of active DBD microplasma area.

Characterization of the Remote Plasma Generated in a Pulsed-DC Gas-Flow Hollow-Cathode Discharge

In this paper, the remote plasma generated in a pulsed-dc powered gas-flow hollow-cathode discharge in Ar with Al and Cu targets used for reactive sputter-deposition processes was investigated using time-resolved optical emission spectroscopy and Langmuir probe measurements. It was found that the Ar emission intensity during the ldquooff-timerdquo of the discharge cycle decays in two steps: A fast decay due to the initial disappearance of the energetic electrons is followed by a subsequent more gradual decay of the plasma density. The plasma potential reaches the highest positive values in the system during the ldquo off-time.rdquo A capacitive current related to the formation of the cathode sheath was detected at the beginning of the ldquoon-timerdquo of the pulsing cycle. At the beginning of plasma re-establishment, the Ar and Al emission intensity peaks coincide with the peak in the electron temperature. At later times, the Ar and Al emission intensities follow the temporal variations of the discharge current.

Progress in Large-Scale Ozone Generation Using Microplasmas

Large-scale ozone generation for municipal and industrial purposes has been entirely based on the creation of microplasmas or microdischarges which are a type of non-thermal or cold plasma created using a reactor known as a dielectric barrier discharge (DBD). Even though microplasma generated ozone has been in continuous use for over a hundred years especially in water treatment, recent shifts in environmental awareness and sustainability have lead to a surge of ozone generating facilities throughout the world. Along with the global expansion of this environmental cleaning application various new discoveries have emerged in the science and technology of ozone generation. This chapter will briefly describe some of the historical and recent developments of this plasma application. A more comprehensive overview of the discharge physics, plasma chemistry, and the biological oxidation capabilities of ozone will be addressed along with a review of some of the most recent breakthrough developments and challenges in large-scale ozone generation technology.

Study of nitrogen reaction kinetics in an industrial ozone generator

Summary form only given. Ozone (O3) is a powerful oxidant that used in a wide array of applications ranging from various industrial chemical synthesis processes to large-scale water treatment. For many years ozone has been generated by means of dielectric barrier discharges (DBD), where a high-energy electric field propagates between two electrodes separated by a dielectric material and a gap containing either pure oxygen or O2 with N2 admixtures. Nitrogen has a significant effect on O3 production as a third body collider. Understanding the reaction kinetics and the role it plays on O3 generation is of primary importance and the focus of this study.A proprietary DBD industrial O3 generator was modified for spectroscopic collection of light emission from the plasma discharges. The light was channeled via fiber optic cable to a UV-Vis spectrometer equipped with an ICCD camera for optical emission spectroscopy (OES) analysis. To analyze the spectra, SpecairTM computational software was used to calculate plasma energies and gas temperatures. To corroborate spectral temperature data calculations, a second identical O3 generator was modified to incorporate a K-type thermocouple to the inner electrode segment and physical temperature measurements were recorded. Additionally, exhaust gas from the O3 generator was channeled into an FTIR spectrometer for production analysis. The N2 second positive (2+) band was chosen as the emission spectral line of choice due to its relatively high intensity compared to excited oxygen species and because it can be used to accurately identify average gas energy distribution and temperature. Initial results suggest close agreement between gas temperatures from both physical measurements and computational spectral analysis. The data also hints at a potential relationship between the plasma energy distribution and the ratio of N2 admixture to the O2 feed gas. As N2 concentration increases, there appears to be a correlating increase in N2 vibrational energies yet a decrease in overall gas temperatures. Further analysis is required to fully define the role of N2 in the chemical kinetics.