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Sang Hee Hong - One of the best experts on this subject based on the ideXlab platform.

  • Operational features and air Plasma Characteristics of a thermal Plasma torch with hollow electrodes
    Plasma Sources Science and Technology, 2003
    Co-Authors: Hur Min, Keun Su Kim, Sang Hee Hong
    Abstract:

    The operational features and thermal Plasma Characteristics of a Plasma torch with hollow electrodes are investigated based on their dependence on input current, gas flow rate and electrode diameter when air is used as a Plasma gas. A Plasma torch with a hollow cathode and anode has been designed and fabricated, and the arc voltages and thermal efficiencies are measured from its discharge. The newly modified similarity criteria are derived from the measured data related to torch performances. From the fact that these criteria successfully describe both the arc voltage and thermal efficiency behaviour of the torch, depending on its operating and geometrical parameters, it is proved that they can be usefully applied to the design and operation of high power torches. For the numerical modelling of the interior region of the torch, a cold flow analysis is employed along with a simplified balance equation of the Lorentz and gas dynamic drag forces in order to determine a cathode spot position on the cathode surface. The validity of this method is confirmed by comparison of the calculated and measured net powers. As a practically useful result of this analysis, carried out through this numerical and experimental work, it is suggested that low input current, high gas flow rate and relatively large electrode diameter are more favourable as appropriate operating conditions of the torch for the efficient treatment of hazardous organic wastes.

  • comparative analysis of turbulent effects on thermal Plasma Characteristics inside the Plasma torches with rod and well type cathodes
    Journal of Physics D, 2002
    Co-Authors: Min Hur, Sang Hee Hong
    Abstract:

    The thermal Plasma Characteristics inside the two non-transferred Plasma torches with rod-type cathode (RTC) and well-type cathode (WTC) are analysed in conjunction with turbulent effects on them in the atmospheric-pressure conditions. A control volume method and a modified semi-implicit pressure linked equations revised algorithm are used for solving the governing equations, i.e. conservation equations of mass, momentum, and energy together with a current continuity equation for arc discharge. A cold flow analysis is introduced to find the cathode spot position in the WTC torch, and both the laminar and turbulent models are employed to gain a physical insight into the turbulent effects on the thermal Plasma Characteristics produced inside the two torches. The numerical analysis for an RTC torch shows that slightly different values of Plasma temperature and velocity between the laminar and turbulent calculations occur and the radial temperature profiles are constricted at the axis with increasing the gas flow rate, and that the large turbulent viscosities appear mostly near the anode wall. These calculated results indicate that the turbulent effects on the thermal Plasma Characteristics are very weak in the whole discharge region inside the RTC torch. On the other hand, the calculated results of the two numerical simulations for a WTC torch present that the significantly different values of Plasma Characteristics between the two models appear in the whole torch region and the Plasma temperatures decrease with increasing the gas flow rate because the relatively strong turbulent effects are prevailing in the entire interior region of the WTC torch. From the comparisons of Plasma net powers calculated and measured in this work, the turbulent modelling turns out to provide the more accurately calculated results close to the measured ones compared with the laminar one, especially for the torch with WTC. This is because the turbulent effects are considerably strong in the WTC torch and subsequently govern the thermal Plasma Characteristics inside it.

  • Numerical imaging of edge Plasma Characteristics in the high-recycling scrape-off layer of the KSTAR tokamak
    IEEE Transactions on Plasma Science, 2002
    Co-Authors: Deok-kyu Kim, Sang Hee Hong
    Abstract:

    Edge Plasma Characteristics of a high-recycling divertor operation regime of the Korea Superconducting Tokamak Advanced Research (KSTAR) tokamak are presented. The results were obtained by numerical simulation using a two-dimensional (2-D) two-fluid edge Plasma transport code coupled with a 2-D Monte Carlo recycling neutral transport code. The simulations successfully display the two major Characteristics of a scrapeoff layer in a high-recycling regime: a parallel temperature gradient and parallel pressure conservation. The results of the simulation can be utilized to provide guidelines for future operation of the KSTAR tokamak regarding the relation between upstream Plasma properties and divertor operation regimes.

  • Effects of anode nozzle geometry on thermal Plasma Characteristics generated by non-transferred torches for material processing
    IEEE Conference Record - Abstracts. 2002 IEEE International Conference on Plasma Science (Cat. No.02CH37340), 1
    Co-Authors: Tae Hyung Hwang, Dong Uk Kim, Jin Myung Park, Soo Seok Choi, Sang Hee Hong
    Abstract:

    Summary form only given. The thermal Plasma Characteristics produced by the nontransferred torches with various anode nozzle geometries, such as a tubular nozzle and a stepped nozzle, operating at an atmospheric pressure are calculated and measured by a numerical simulation and an optical emission spectroscopy, respectively. On the basis of the assumption of local thermodynamic equilibrium (LTE) and optically thin Plasmas, the temperature distributions of argon thermal Plasmas are determined by the Abel inversion and Boltzmann plot methods for the measured intensity of Ar I lines.

  • Numerical analysis on Plasma Characteristics of high power Plasma torch of hollow electrode type for waste treatment
    IEEE Conference Record - Abstracts. 1997 IEEE International Conference on Plasma Science, 1
    Co-Authors: M. Hur, K.d. Kang, Sang Hee Hong
    Abstract:

    Summary form only given. Waste treatment is certainly one of the most promising areas of thermal Plasma application, which aims either at the reclamation of waste materials for recovering higher valued products or at the destruction of toxic wastes and the generation of environmentally safe by-products. The high power Plasma torches have been widely used for the incineration of waste materials to pyrolyze organic toxins and the vitrify the solid materials through their volume reduction in a not-leacheable compact state. In this study, the Plasma Characteristics of a high power nontransferred Plasma torch with hollow electrodes are investigated in the atmospheric condition by analyzing the distributions of Plasma temperature, velocity and current density.

Jan Van Impe - One of the best experts on this subject based on the ideXlab platform.

  • Influence of Plasma Characteristics on the Inactivation Mechanism of Cold Atmospheric Plasma (CAP) for Listeria monocytogenes and Salmonella Typhimurium Biofilms
    Applied Sciences, 2020
    Co-Authors: Marlies Govaert, Cindy Smet, James L. Walsh, Jan Van Impe
    Abstract:

    This research aimed to take a next step towards unravelling the CAP inactivation mechanism for mature (Listeria monocytogenes (Gram positive) and Salmonella Typhimurium (Gram negative)) model biofilms, which will support the further optimization this novel technology. More specifically, we examined how the inactivation mechanism was influenced by the applied processing conditions, i.e., by the electrode configuration, the composition of the gas flow, and the power of the discharge. For each combination of Plasma Characteristics, we examined if the applied CAP treatment had an effect on (i) the cell membrane, (ii) the intracellular DNA, and (iii) the EPS matrix. In addition, we assessed which (reactive) CAP species were responsible for this lethal/damaging effect and whether these species were able to diffuse into the deeper layers of the biofilms. The results indicated that the inactivation mechanism was indeed influenced by the applied processing conditions. Nevertheless, the bactericidal effect of CAP was always a combination of both damage to the membrane and the DNA, caused by (i) the generation of (intracellular) ROS and RNS, (ii) a drop in pH, and/or (iii) the potential generation of a small amount of UV photons. Moreover, the Plasma species were able to penetrate into the deeper layers of the model biofilms and some treatment conditions resulted in an increased biofilm porosity.

  • Influence of Plasma Characteristics on the efficacy of Cold Atmospheric Plasma (CAP) for inactivation of Listeria monocytogenes and Salmonella Typhimurium biofilms
    Innovative Food Science & Emerging Technologies, 2019
    Co-Authors: Marlies Govaert, Cindy Smet, Laurens Vergauwen, Branimir Ecimovic, James L. Walsh, Maria Baka, Jan Van Impe
    Abstract:

    Abstract The biofilm mode of growth protects bacterial cells from applied disinfection methods for abiotic (food) contact surfaces. Therefore, new inactivation technologies such as Cold Atmospheric Plasma (CAP) should be considered. However, the influence of different Plasma Characteristics on the CAP efficacy for biofilm inactivation requires further study. In this research, the influence of (i) the applied Plasma configuration (Dielectric Barrier Discharge (DBD) and Surface Barrier Discharge (SBD)), (ii) the oxygen level of the gas flow (He + 0.0/0.5/1.0 (v/v) % O2), and (iii) the Plasma intensity (13.88, 17.88, and 21.88 V input voltage) on the CAP efficacy for inactivation of L. monocytogenes and S. Typhimurium biofilms was investigated. Depending on the applied Plasma Characteristics, log10-reductions up to approximately 3.5 log(CFU/cm2) were obtained. Nevertheless, it could be concluded that the highest log-reductions were in general obtained while using the DBD electrode, 0.0 (v/v) % O2, and an input voltage of 21.88 V. Industrial relevance This study demonstrated the potential application of CAP for inactivation of pathogenic biofilms developed on abiotic (food) contact surfaces. The effect of different Plasma Characteristics on the CAP inactivation efficacy was investigated and determined optimal conditions resulted in promising reductions of the biofilm-associated cells. By incorporating this novel technology in a complete cleaning and disinfection process, the risk of (cross) contamination of food products might extensively be reduced.

P De Paz - One of the best experts on this subject based on the ideXlab platform.

  • The percentage of spermatozoa lost during the centrifugation of brown bear (Ursus arctos) ejaculates is associated with some spermatozoa quality and seminal Plasma Characteristics.
    Animal reproduction science, 2012
    Co-Authors: M Alvarez, M Nicolas, S Borragán, E Lopez-urueña, L Anel-lópez, F Martinez-pastor, J Tamayo-canul, L Anel, P De Paz
    Abstract:

    Cryopreservation of brown bear (Ursus arctos) semen requires centrifugation to increase concentration and/or remove urine contamination. However, a percentage of the spermatozoa are lost in the process. This percentage varies considerably between males and ejaculates, and we have studied the effect of sperm quality and seminal Plasma Characteristics on the spermatozoa recovery rate after centrifugation. One hundred and thirty one sperm samples obtained from fifteen brown bear males by electroejaculation under general anaesthesia were used. The ejaculates were centrifuged 600 × g for 6 min. Motility was assessed by CASA, and acrosomal status (PNA-FITC) and viability (SYBR-14/propidium iodide) were determined by flow cytometry. Seminal Plasma Characteristics (albumin, alkaline phosphatase, calcium, cholesterol, creatine, glucose, glutamic oxaloacetic transaminase (GOT), lactate, lipase, magnesium, phosphate and total protein) were determined by a biochemical and gas analysis. Total motility (r = 0.26; P=0.005) and cell viability (r = 0.20; P = 0.033) were positively correlated with the percentage of recovered spermatozoa. Sperm recovery was correlated with the concentration of several components of seminal Plasma: negatively with glucose concentration (r = -0.47; P = 0.005) and positively with the enzymes GOT (r = 0.36; P = 0.040) and lactate dehydrogenase (r = 0.36; P = 0.041). After sorting the data into classes according to sperm recovery (Low: 0-39, Medium: 40-69, High: 70-100), we observed that the samples with a lower recovery rate derived from ejaculates with lower values for TM, VAP and viability (P

  • The percentage of spermatozoa lost during the centrifugation of brown bear (Ursus arctos) ejaculates is associated with some spermatozoa quality and seminal Plasma Characteristics.
    Animal Reproduction Science, 2012
    Co-Authors: M Alvarez, M Nicolas, S Borragán, E Lopez-urueña, L Anel-lópez, F Martinez-pastor, J Tamayo-canul, L Anel, P De Paz
    Abstract:

    Cryopreservation of brown bear (Ursus arctos) semen requires centrifugation to increase concentration and/or remove urine contamination. However, a percentage of the spermatozoa are lost in the process. This percentage varies considerably between males and ejaculates, and we have studied the effect of sperm quality and seminal Plasma Characteristics on the spermatozoa recovery rate after centrifugation. One hundred and thirty one sperm samples obtained from fifteen brown bear males by electroejaculation under general anaesthesia were used. The ejaculates were centrifuged 600 × g for 6 min. Motility was assessed by CASA, and acrosomal status (PNA-FITC) and viability (SYBR-14/propidium iodide) were determined by flow cytometry. Seminal Plasma Characteristics (albumin, alkaline phosphatase, calcium, cholesterol, creatine, glucose, glutamic oxaloacetic transaminase (GOT), lactate, lipase, magnesium, phosphate and total protein) were determined by a biochemical and gas analysis. Total motility (r = 0.26; P = 0.005) and cell viability (r = 0.20; P = 0.033) were positively correlated with the percentage of recovered spermatozoa. Sperm recovery was correlated with the concentration of several components of seminal Plasma: negatively with glucose concentration (r = −0.47; P = 0.005) and positively with the enzymes GOT (r = 0.36; P = 0.040) and lactate dehydrogenase (r = 0.36; P = 0.041). After sorting the data into classes according to sperm recovery (Low: 0–39, Medium: 40–69, High: 70–100), we observed that the samples with a lower recovery rate derived from ejaculates with lower values for TM, VAP and viability (P < 0.05). Multiple regression analysis rendered two models to define the post-centrifugation spermatozoa recovery which included total motility and damaged acrosome or glucose, GOT and lactate dehydrogenase. We discuss these relationships and their implications in the electroejaculation procedure and the handling of the sample during centrifugation.

Hirokazu Tahara - One of the best experts on this subject based on the ideXlab platform.

  • Effects of channel wall material on thrust performance and Plasma Characteristics of Hall-effect thrusters
    Vacuum, 2006
    Co-Authors: Hirokazu Tahara, Katsumi Imanaka, Seiro Yuge
    Abstract:

    The effects of channel wall material on Hall thruster performance and on Plasma Characteristics were investigated. A laboratory-model Hall thruster THT-III was operated with three channel wall materials of BN, BNSiN and BNAlN. Both the discharge current and the thrust were affected by the nature of the channel wall materials. The measured axial distributions of wall and Plasma potentials, radial and axial electron temperatures, and electron number density near the channel walls showed that the wall material affected ionization region and ion wall loss in the channel, resulting from secondary electron emission, although ion acceleration region was determined by the axial distribution of radial magnetic field. The difference in discharge current between channel wall materials was attributed to the difference in axial current density near the inner channel wall, depending on secondary electron emission.

  • Relationships between Thrust Performance and Plasma Characteristics in the Vicinity of Acceleration Channel Wall of a Hall Thruster
    JOURNAL OF THE JAPAN SOCIETY FOR AERONAUTICAL AND SPACE SCIENCES, 2006
    Co-Authors: Seiro Yuge, Katsumi Imanaka, Hirokazu Tahara
    Abstract:

    For a Hall thruster, the influences of discharge channel wall material on thrust performance and Plasma Characteristics in the vicinity of the channel wall were investigated. In this study, THT-III 1-kW class Hall thruster was operated with three dielectric channel walls of BN, BNAlN and BNSiN. Discharge current and thrust were measured; specific impulses and thrust efficiencies were evaluated. The Plasma potential, channel wall potential, electron temperature and electron number density were measured with an electrostatic single probe. The process of ion generation and acceleration in a Hall thruster was discussed with measured results. The thrust performances were affected by nature of the channel walls. Measured Plasma Characteristics suggested that the channel wall material affected an ionization region and ion wall losses in the channel, resulting from secondary electron emission. The difference of discharge current between channel materials was considered to be caused by the difference of current density near the inner channel wall.

  • Performance and Plasma Characteristics of Pulsed Magneto-Plasma-Dynamic Arcjet Thrusters with Cusp and Divergent-Nozzle Applied-Magnetic-Fields
    JOURNAL OF THE JAPAN SOCIETY FOR AERONAUTICAL AND SPACE SCIENCES, 2006
    Co-Authors: Hirokazu Tahara, Hiroyuki Morisaki, Yoichi Kagaya
    Abstract:

    A two-stage magnetic field with cusp and divergent shapes was applied in a magneto-Plasma-dynamic (MPD) thruster discharge chamber. The thrust efficiency intensively increased with enhanced thrust and unchanged discharge voltage because of more effective ionization/heating and swirl acceleration due to the applied magnetic field. When the magnetic field became much stronger and the arc current became much higher, the thrust approached the self-magnetic thrust. As a result, an optimum magnetic field strength existed. The Plasma flow was observed by a high-speed camera, and Plasma density, temperature and velocity were measured with electrostatic probes. Through the magnetic nozzle the exhausted Plasma rotated and spreaded radially-outward, and the Plasma density decreased near the central axis. Accordingly, the Plasma Characteristics agreed with the measured thrust performance, considering intensive Plasma heating due to Hall current and swirl acceleration, i.e. conversion from azimuthal kinetic energy to axial kinetic energy.

  • Effects of Channel Wall Material on Performance and Plasma Characteristics of Hall Thrusters
    2005
    Co-Authors: Hirokazu Tahara, Katsumi Imanaka
    Abstract:

    The effects of channel wall material on Hall thruster performance and on Plasma Characteristics were investigated. A laboratory-model Hall thruster THT-III was operated with three channel wall materials of BN, BNSiN and BNAlN. Both the discharge current and the thrust were affected by the nature of the channel wall materials. The measured axial distributions of wall and Plasma potentials, radial and axial electron temperatures, and electron number density near the channel walls showed that the wall material affected ionization region and ion wall loss in the channel, resulting from secondary electron emission, although ion acceleration region was determined by the axial distribution of radial magnetic field. The difference in discharge current between channel wall materials was considered to be caused by the difference in axial current density near the inner channel wall, depending on secondary electron emission.

  • Plasma Characteristics of Supersonic Nitrogen/Hydrogen-Mixture and Ammonia Plasma Jets and Nitrided Material Properties
    Materials Science Forum, 2004
    Co-Authors: Hirokazu Tahara, Yasutaka Ando, Takao Yoshikawa
    Abstract:

    Spectroscopic and electrostatic probe measurements were made to examine Plasma Characteristics under nitriding for a 10-kW-class direct-current arc Plasma jet generator with a supersonic expansion nozzle in a low pressure environment. Heat fluxes into the plate from the Plasma were also evaluated. Ammonia and mixtures of nitrogen and hydrogen were used as the working gas. The H-atom electronic excitation temperature and the N2 molecule-rotational excitation temperature intensively decreased downstream in the nozzle although the NH molecule-rotational excitation temperature did not show an axial decrease. As approaching the titanium plate, the thermodynamical nonequilibrium Plasma came to be a temperature-equilibrium one. Both the electron number density near the plate and the heat flux increased with H2 mole fraction for mixtures gases. In cases with mixtures of N2 and H2, a radical of NH with a radially wide distribution is considered to contribute to the better nitriding as a chemically active and non heating process.

Min Suk Cha - One of the best experts on this subject based on the ideXlab platform.

  • Microwave Plasma Jet in Water: Effect of Water Electrical Conductivity on Plasma Characteristics
    Plasma Chemistry and Plasma Processing, 2019
    Co-Authors: Ahmad Hamdan, Jacopo Profili, Min Suk Cha
    Abstract:

    Plasma-induced water treatment is a novel water treatment technique that has shown high efficiency and flexibility. Although the electrical conductivity of impure water varies depending on the degree of pollution, its influence on Plasma treatment efficiency is not well understood. In this study, we investigate the fundamentals of a microwave Plasma jet submerged in water with electrical conductivities (σw) ranging from 10 to 10,000 µS/cm. The Plasma Characteristics, namely composition, electron density, and temperature, and their variations as a function of σw, are derived using optical emission spectroscopy. The Plasma-bubble dynamics is investigated using space- and time-resolved high-speed imaging. The results show that the Plasma fills the bubble volume at relatively low flow rate (typically,   1000 µS/cm). The influence of σw on the degradation of methylene blue, a standard water pollutant, is also assessed, and the obtained results indicate that the Plasma becomes extremely inefficient at high σw. These findings are of great importance for the community of Plasma-induced liquid processing, particularly wastewater treatment.