A 1-D fluid model for homogeneous dielectric barrier discharge (DBD) in helium is presented, aimed at unraveling the spatial-temporal characteristics of two basic discharge regimes: single-breakdown and multi-breakdown discharges. Discharge currents, gap voltages, charge densities, electron temperature and electric field profiles of the two regimes make it clear that these two regimes are qualitatively different. It is found that the multi-breakdown discharge has a more homogeneous flux on dielectrics compared to the single-breakdown discharge.

Wang Xiaohua;Yang Aijun;Rong Mingzhe;Liu Dingxing

Plasma Science and Technology

2011

This paper is devoted to the calculation of the chemical equilibrium composition and thermodynamic properties of reacting mixtures of carbon and water at high temperature. Equilibrium particle concentrations and thermodynamic properties including mass density, molar weight, entropy, enthalpy and specific heat at constant pressure, sonic velocity, and heat capacity ratio are determined by the method of Gibbs free energy minimization, using species data from standard thermodynamic tables. The calculations, which assume local thermodynamic equilibrium, are performed in the temperature range from 400 to 30,000 K for pressures of 0.10, 1.0, 3.0, 5.0 and 10.0 atm. The properties of the reacting mixture are affected by the possible occurrence of solid carbon formation at low temperature, and therefore attention is paid to the influence of the carbon phase transition by comparing the results obtained with and without considering solid carbon formation. The results presented here clarify some basic chemical process and are reliable reference data for use in the simulation of plasmas in reacting carbon and water mixtures together with the need of transport coefficients computation. © Springer Science+Business Media, LLC 2011.

Wang Wei Zong;Rong Ming Zhe;Yan J. D.;Spencer J. W.;Fang M. T.C.;Murphy A. B.

Plasma Chemistry and Plasma Processing

2012

This study focuses on the generation and loss of reactive oxygen species (ROS) in low-temperature atmospheric-pressure RF (13.56MHz) He+O 2+H 2O plasmas, which are of interest for many biomedical applications. These plasmas create cocktails of ROS containing ozone, singlet oxygen, atomic oxygen, hydroxyl radicals, hydrogen peroxide and hydroperoxyl radicals, i.e. ROS of great significance as recognized by the free-radical biology community. By means of one-dimensional fluid simulations (61 species, 878 reactions), the key ROS and their generation and loss mechanisms are identified as a function of the oxygen and water content in the feed gas. Identification of the main chemical pathways can guide the optimization of He+O 2+H 2O plasmas for the production of particular ROS. It is found that for a given oxygen concentration, the presence of water in the feed gas decreases the net production of oxygen-derived ROS, while for a given water concentration, the presence of oxygen enhances the net production of water-derived ROS. Although most ROS can be generated in a wide range of oxygen and water admixtures, the chemical pathways leading to their generation change significantly as a function of the feed gas composition. Therefore, care must be taken when selecting reduced chemical sets to study these plasmas. © 2012 IOP Publishing Ltd.

McKay K.;Iza F.;Kong M. G.;Liu D. X.;Rong M. Z.

Journal of Physics D Applied Physics

2012

The accuracy of numerical simulation on plasma behavior depends strongly on the reliability of thermophysical property data. Large number of studies for thermal plasma properties in the local thermodynamic equilibrium (LTE) exist; however, the database for thermal nonequilibrium plasmas is still far from completeness. This paper derives a general expression of total reactive thermal conductivity (TRTC) with great applicability to monatomic, diatomic, and polyatomic gases in terms of a two-temperature model. The derived formula is applied to nitrogen plasmas under thermal equilibrium and nonequilibrium conditions, considering its wide use in plasma systems and switching devices. Typical calculated results of TRTC with two different Saha equations and Guldberg-Waage equations in the temperature range of 300 K-40000 K under different degrees of nonequilibrium are given and compared with those computed according to Brokaw and Butler's derivation for the special case of LTE plasmas, which shows excellent agreement. The influence of different expressions for Saha equations and Guldberg-Waage equations, together with different pressures of 0.1, 1, 3, 5, and 10 atm, on the TRTC evaluated by this newly developed expression is presented as well. These provide reliable reference data for use in the simulation of plasmas. © 2012 IEEE.

Wang Weizong;Rong Mingzhe;Wu Yi;Yan Jiu Dun

IEEE Transactions on Plasma Science

2012

The present contribution is continuation of Part 1: Equilibrium composition and thermodynamic properties. This paper is devoted to the calculation of transport properties of mixtures of water and carbon at high temperature. The transport properties, including electron diffusion coefficient, viscosity, thermal conductivity, and electrical conductivity are obtained by using the Chapman-Enskog method expanded to the thirdorder approximation (second-order for viscosity), taking only elastic processes into account. The calculations, which assume local thermodynamic equilibrium, are performed for atmospheric pressure plasmas in the temperature range from 400 to 30,000 K for pressures of 0. 10, 1.0, 3.0, 5.0 and 10.0 atm. with the results obtained are compared to those of previously published studies, and the reasons for discrepancies are analyzed. The results provide reliable reference data for simulation of plasmas in mixtures of carbon and water. © Springer Science+Business Media, LLC 2011.

Wang WeiZong;Rong Ming Zhe;Yan J. D.;Spencer J. W.;Murphy A. B.

Plasma Chemistry and Plasma Processing

2012

The transport properties including electron diffusion coefficient, viscosity, thermal conductivity, and electrical conductivity of CF 4 , C 2 F 6 , and C 3 F 8 plasmas are obtained by using the Chapman-Enskog method expanded up to the third-order approximation (second-order for viscosity). The most recent data on potential interactions and elastic differential cross sections for interacting particles were utilized. The calculations, which assume local thermodynamic equilibrium, are performed at atmospheric pressure in the temperature range from 300 to 30 000 K. Our results can provide reliable reference data for the further simulation to study the relevant plasmas behavior. © 2011 IEEE.

Wang WeiZong;Rong MingZhe;Wu Yi;Spencer J. W.;Yan J. D.

2011 1st International Conference on Electric Power Equipment Switching Technology Icepe2011 Proceedings

2011

For monitoring temperature, insulation and mechanism of medium voltage switchgear, an on-line monitoring system was developed. Based on the low power electronic devices and infrared communication, a contact-type temperature sensor with high precision was designed for the system to solve the problem of high voltage isolation. An angular displacement sensor was used to measure the travel-time curve of the movable contacts indirectly, leading to the solutions of the problems in sensor assembling and high voltage isolation. Furthermore, combining with the vibration signal and the current curve of tripping coils during operation, the monitoring of mechanism condition of medium voltage switchgear could be achieved. The insulation could be characterized by measuring the leakage current of bushing. The test indicates that the on-line monitoring system is stable and reliable.

Wang Xiao-Hua;Su Biao;Rong Ming-Zhe;Liu Ding-Xin;Qiu Juan;Wang Cong-Gang

Gaoya Dianqi High Voltage Apparatus

2009

The calculated values of thermodynamic and transport properties of pure F 2 and fluorocarbon compounds CF 4, C 2F 2, C 2F 4, C 2F 6, C 3F 6 and C 3F 8 at high temperatures are presented in this paper. The thermodynamic properties are determined by the method of Gibbs free energy minimization, using standard thermodynamic tables. The transport properties, including electron diffusion coefficients, viscosity, thermal conductivity and electrical conductivity, are evaluated using the Chapman-Enskog method expanded up to the third-order approximation (second order for viscosity). The most accurate cross-section data that could be located are used to evaluate collision integrals. The calculations based on the assumption of local thermodynamic equilibrium are performed for atmospheric-pressure plasmas in the temperature range from 300 to 30000K for different pressures between 0.1 and 10atm. The results of F 2, CF 4, C 2F 2, C 2F 4 and C 2F 6 are compared with those of previously published studies. Larger discrepancies occur for transport coefficients; these are explained in terms of the different values of the collision integrals that were used. The results presented here are expected to be more accurate because of the improved collision integrals employed. © 2012 IOP Publishing Ltd.

Wang Weizong;Wu Yi;Rong Mingzhe;\u00c9hn L\u00e1szl\u00f3;\u010cernu\u0161\u00e1k Ivan

Journal of Physics D Applied Physics

2012

A radio-frequency (rf) atmospheric-pressure discharge in He-O 2 mixture is studied using a fluid model for its wall fluxes and their dependence on electron and chemical kinetics in the sheath region. It is shown that ground-state O, and ^O are the dominant wall fluxes of neutral species, cations and anions, respectively. Detailed analysis of particle transport shows that wall fluxes are supplied from a boundary layer of 3-300m immediately next to an electrode, a fraction of the thickness of the sheath region. The width of the boundary layer mirrors the effective excursion distance during lifetime of plasma species, and is a result of much reduced length scale of particle transport at elevated gas pressures. As a result, plasma species supplying their wall fluxes are produced locally within the boundary layer and the chemical composition of the overall wall flux depends critically on spatio-temporal characteristics of electron temperature and density within the sheath. Wall fluxes of cations and ions are found to consist of a train of nanosecond pulses, whereas wall fluxes of neutral species are largely time-invariant. © 2012 IOP Publishing Ltd.

Liu D. X.;Yang A. J.;Wang X. H.;Rong M. Z.;Kong M. G.;Iza F.

Journal of Physics D Applied Physics

2012

This paper deals with thermodynamic and transport properties of SF 6 plasmas in a two-temperature model for both thermal equilibrium and non-equilibrium conditions. The species composition and thermodynamic properties are numerically determined using the two-temperature Saha equation and Guldberg-Waage equation according to deviation of van de Sanden Transport properties including diffusion coefficient, viscosity, thermal conductivity, and electrical conductivity are calculated with most recent collision interaction potentials by adopting Devoto's electron and heavy particle decoupling approach but expanded to the third-order approximation (second-order for viscosity) in the frame of Chapman-Enskog method. The results are computed for various values of pressures from 0.1 atm to 10 atm and ratios of the electron temperature to the heavy particle temperature from 1 to 20 with electron temperature range from 300 to 40 000 K. In the local thermodynamic equilibrium regime, results are compared with available results of previously published studies. © 2012 American Institute of Physics.

Wang Weizong;Rong Mingzhe;Wu Yi;Spencer Joseph W.;Yan Joseph D.;Mei Danhua

Physics of Plasmas

2012