A. Maslani

Characteristics of atmospheric pressure air discharges with a liquid cathode and a metal anode

Electrical and optical emission properties of a burning plasma between a liquid cathode and a metal anode are presented in this paper. The plasma has constricted contact points at the liquid cathode and is clearly filamentary in nature near the water surface.The cathode voltage drop depends on conductivity rather than pH and is significantly different for distilled water and electrolyte solutions. An acidification of the liquid due to the plasma is always observed.The rotational temperature of OH and N2 in the bulk of the plasma is, respectively, in the range 3200?3750?K and 2500?2750?K. The rotational temperature of nitrogen near the metal anode is typically two times smaller. Electron densities near the cathode measured by Stark broadening of H? are in the range (5.5?8.0) ? 1014?cm?3, the atomic excitation temperatures in the range 5750?7250?K. Differences in electrical and optical emission properties between the cases when distilled water and electrolyte solutions are used as cathode are discussed in detail.

Integrated parametric study of a hybrid-stabilized argon?water arc under subsonic, transonic and supersonic plasma flow regimes

This paper presents a numerical investigation of characteristics and processes in the worldwide unique type of thermal plasma generator with combined stabilization of arc by argon flow and water vortex, the so-called hybrid-stabilized arc. The arc has been used for spraying of ceramic or metallic particles and for pyrolysis of biomass. The net emission coefficients as well as the partial characteristics methods for radiation losses from the argon?water arc are employed. Calculations for 300?600?A with 22.5?40 standard litres per minute (slm) of argon reveal transition from a transonic plasma flow for 400?A to a supersonic one for 600?A with a maximum Mach number of 1.6 near the exit nozzle of the plasma torch. A comparison with available experimental data near the exit nozzle shows very good agreement for the radial temperature profiles. Radial velocity profiles calculated 2?mm downstream of the nozzle exit show good agreement with the profiles determined from the combination of calculation and experiment (the so-called integrated approach). A recent evaluation of the Mach number from the experimental data for 500 and 600?A confirmed the existence of the supersonic flow regime.

Experimental study of the effect of gas nature on plasma arc cutting of mild steel

This paper is devoted to the experimental investigation of arc cutting of mild steel using plasmas generated in gas and liquid media. Due to different chemical compositions, the examined media have different thermophysical properties, which affect the properties of the generated plasma and cutting performance. The experiments are performed on 15mm mild steel plates using commercial equipment at 60A to approach real operation conditions in application areas. The studied gases are chosen according to recommendations of the world’s leading manufacturers of arc cutting equipment for mild steel. Specific differences between plasma gases are discussed from the point of view of properties of the gas and the generated plasma, amount of removed material, kerf shape and overall energy balance of the cutting process. The paper describes the role of exothermic reaction of iron oxidation for oxygen cutting and explains its neglect for liquid cutting. This paper explains the potential of facilitating the cutting process by modification of the plasma gas chemical composition and flow rate. (Some figures may appear in colour only in the online journal)

Steam Plasma Treatment of Organic Substances for Hydrogen and Syngas Production

Gasification of several organic materials in steam plasma generated in a special plasma torch with a water-stabilized arc was investigated. Thermal plasma with very high enthalpy and low mass flow rate is produced in an arc discharge which is in direct contact with water. Biomass and several types of solid and liquid organic waste were gasified by plasma aided reactions of materials with water, carbon dioxide and oxygen. Composition of produced gas, energy balance of gasification process and gasification efficiency were determined from measured data. Synthesis gas with high content of hydrogen and carbon monoxide and very low content of carbon dioxide, light hydrocarbons and tar was obtained for all tested materials. Comparison of measured data with results of theoretical computations confirmed that steam plasma gasification produces syngas with composition which is close to the one obtained from thermodynamic equilibrium calculations.

Emission Spectroscopy of OH Radical in Water-Argon Arc Plasma Jet

Emission spectra of OH radical are studied in the plasma jet generated by a plasma torch with hybrid water-argon stabilization. Plasma jet is located in a chamber with pressures 4 kPa and 10 kPa. In spite of high temperatures of produced plasma, OH spectra are observed in a large area of the jet. OH spectra are used to obtain rotational temperatures from the Boltzmann plots of resolved rotational lines. Due to line-of-sight integration of radiation, interpretation of the temperatures is not straightforward. It seems that excited OH molecules can be formed by various mechanisms, mainly in the outer parts of the jet, where thermal processes are not as dominant as in the hot central region.

Degradation of Verapamil hydrochloride in water by gliding arc discharge

This study investigated the influence of gliding arc plasma discharge on the degradation of Verapamil hydrochloride in water. The plasma discharge was characterized by means of optical emission spectroscopy. Spectra of various atomic and molecular species were observed. Aqueous solution of Verapamil hydrochloride was exposed to gliding arc discharge operated in continuous discharge at atmospheric pressure and room temperature. The identification of Verapamil, the degradation mechanisms of Verapamil and its transformation products were performed using liquid chromatography - mass spectrometry (HPLC-MS). Experimental results indicate that the atmospheric pressure gliding arc plasma treatment has noticeable effects on Verapamil with satisfactory degradation efficiency. Plausible mechanisms of the degradation were discussed.

Experimental investigation of energy balance in plasma arc cutting process

The present paper describes the power balance of the arc cutting process provided by a plasma torch with steam working medium. The work was concentrated on definition of different power terms including power input as well as effective power utilization and losses as a function of plasma gas flow rate. The work was mostly experimental. The results have shown around 20% of total available power is utilized for material cutting and removing for the studied conditions.

Numerical Investigation of Hybrid-Stabilized Argon-Water Electric Arc Used for Biomass Gasification

Plasma generators with arc discharge stabilization by water vortex exhibit special performance characteristics; such as high outlet plasma velocities (up to 7 000 m ⋅ s-1), temperatures (~ 30 000 K), plasma enthalpy and, namely, high powder throughput, compared to commonly used gas-stabilized (Ar, He) torches (Hrabovský et al., 1997). In a water-stabilized arc, the stabilizing wall is formed by the inner surface of water vortex which is created by tangential water injection under high pressure (~ 10 atm.) into the arc chamber. Evaporation of water is induced by the absorption of a fraction of Joule power dissipated within the conducting arc core. Further heating and ionization of the steam are the principal processes which produce water plasma. The continuous inflow and heating lead to an overpressure and plasma is accelerated towards the nozzle exit. The arc properties are thus controlled by the radial energy transport from the arc core to the walls and by the processes influencing evaporation of the liquid wall. A combination of gas and vortex stabilization has been utilized in the so-called hybridstabilized electric arc, its principle is shown in Fig.1. In the hybrid H2O-Ar plasma arc the discharge chamber is divided into the short cathode part where the arc is stabilized by tangential argon flow in the axial direction, and the longer part which is water-vortexstabilized. This arrangement not only provides additional stabilization of the cathode region and protection of the cathode tip, but also offers the possibility of controlling plasma jet characteristics in wider range than that of pure gas or liquid-stabilized torches (Březina et al., 2001; Hrabovský et al., 2003). The arc is attached to the external water-cooled rotating disc anode a few mm downstream of the torch orifice. The characteristics of the hybridstabilized electric arc were measured and the effect of gas properties and flow rate on plasma properties and gas-dynamic flow characteristics of the plasma jet were studied. Experiments (Březina et al., 2001; Hrabovský et al., 2006) proved that plasma mass flow rate,

A comparative numerical study of hybrid-stabilized argon–water electric arc

Abstract The paper presents numerical simulations of the discharge and the near-outlet regions of the hybrid-stabilized argon–water electric arc. Two different numerical methods for solving the set of conservative equations for the continuity, momentum and energy have been applied. The major difference between the results using the two methods occurs in the temperature distribution in arc fringes within the discharge chamber. This fact influences the potential drop, overpressure, reabsorption of radiation and arc efficiency. It is shown that the radial profiles of temperature at the exit nozzle are less influenced by different temperature distribution within the discharge chamber. Comparison with chosen experimental temperature profiles shows very good agreement.

Time-Resolved Emission Spectroscopy Measurements during the Restrike Period in Arc Plasma Torch

Simultaneous optical, spectroscopic, and electrical measurements in the region of the arc anode attachment of the water-argon plasma torch are presented. A movement of the arc attachment along the anode surface together with its restrike mode is monitored. Temporal evolution of temperature during one cycle of the restrike mode is obtained in three different axial positions in the plasma column. Resulting temperature profiles show how the position of the arc attachment influences the plasma properties.