3D static and time-dependent modelling of a dc transferred arc twin torch system

International audienceThe transferred arc plasma torch device consists of two electrodes generating a plasma arc sustained by means of an electric current flowing through the body of the discharge. Modeling works investigating of transferred electric arc discharges generated between two suspended metallic electrodes, in the so called twin torch configuration, are scarce. The discharge generated by this particular plasma source configuration is characterized by a complex shape and fluid dynamics and needs a 3D description in order to be realistically predicted. The extended discharge length that goes from the tungsten pencil cathode to the flat copper anode without any particular confinement wall and the fluid dynamics and magnetic forces acting on the arc may induce an unsteady behavior. In order to capture the dynamic behavior of a twin torch discharge, a 3D time dependent plasma arc model has been developed using a customized commercial code FLUENT form in both Local Thermodynamic Equilibrium (LTE) and non-LTE. A two temperature (2T) model has been developed taking into account only the thermal non-equilibrium effects in argon plasma. The main differences between LTE and 2T models results concern the increased extension of the horizontal section of the discharge and the predicted reduced (of about 60-80V) voltage drop between the electrodes when using a 2T model

Modelling of induction thermal plasma synthesis of iron nanoparticles in oxygen-contaminated gas mixtures

The synthesis of iron nanoparticles in a radio-frequency induction thermal plasma (RF-ITP) system working in a mixture of argon contaminated with oxygen (10-100 ppm) has been modelled considering the iron oxidation reactions both in gaseous and condensed phases. The results show that oxidation occurs mainly in the gas phase where Fe is converted to FeO. As the concentration of oxygen impurities increases, the nucleation region is shifted towards higher temperatures and the resulting nanoparticles are characterized by larger diameters

Quench rate affects oxidation reactions in the formation of arc welding fumes

The formation process of fumes in gas metal arc welding (GMAW) has been modelled considering the iron oxidation reactions both in gaseous and condensed phases. The results show that fumes are composed of aggregates of primary particles that are nucleated from gas-phase FeO and further oxidized to Fe 3 O 4 or Fe 2 O 3 , depending on the quench rate. Increasing the latter results in two effects: on one side, it induces the formation of smaller primary particles, which are more easily oxidised, but at the same time it reduces the time for solid-state diffusion of oxygen, resulting in lower particle oxidation

3-D Static and time-depending modelling of DC and RF thermal plasmas for industrial applications

Thermal plasma processes play nowadays a key role in many industrial applications, such as powder densification and spheroidization, synthesis of nano-powders, treatment of waste materials and spraying of thin coatings. Although many of these applications have been fully implemented industrially for many decades, modelling plays an important factor in their continued development and improvement. 3-D simulation of the behaviour of commercial inductively coupled (RF) plasma can be useful tool to predict the main features of plasma assisted treating and processing of injected raw materials. The effects of changing coil current frequency, the hydrogen mixing in argon primary gas and the flow patterns and temperature distributions have been investigated. 3-D time-dependent modelling DC non-transferred arc plasma torch for plasma spraying operating at atmospheric pressure can allow the prediction of particle trajectories and thermal history, the analysis of the influence of the plasma jet cold gas entrained eddies on particle behaviour and the mechanisms that can lead to a fluctuating and non homogeneous heating of the particle stream. All computations have been performed using a customized version of the CFD commercial code FLUENT\ua9

Two-temperature thermodynamic and transport properties of carbon-oxygen plasmas

Thermodynamic and transport properties of different carbon-oxygen plasmas mixtures are presented for both thermal equilibrium and non-equilibrium conditions: to the knowledge of the authors, the latter data have not been reported in the literature. The calculations of transport properties are carried out using the Chapman-Enskog method up to the third order; properties for plasmas out of equilibrium have been obtained using both the two-temperature theory developed by Rat et al and a simplified theory by Devoto, that neglects the coupling between electrons and heavy particles; it is shown that for carbon-oxygen mixtures no differences between results obtained using these two theories can be appreciated for thermal and electrical conductivities; some discrepancies have been found for ordinary diffusion coefficients of the type electron-heavy particle. Moreover, local thermodynamic equilibrium results for transport properties obtained using Lennard-Jones potentials have been compared with results obtained using more recent potential data and with available results reported in the literature. Results for composition, mass density, specific heat, thermal conductivity, electrical conductivity and viscosity of atmospheric pressure plasmas in the electron temperature range 300-30 000 K are reported

Two-temperature thermodynamic and transport properties of argon\u2013hydrogen and nitrogen\u2013hydrogen plasmas

Two-temperature thermodynamic and transport properties of argon\u2013hydrogen and nitrogen\u2013hydrogen plasma mixtures are presented, chemical equilibrium being achieved. The calculations of transport properties are carried out using the Chapman\u2013Enskog method up to the third order; when electron temperature differs from that of heavy particles, calculations are performed following both a recent two-temperature theory by Rat et al that retains the coupling between electrons and heavy particles and a simplified decoupling theory proposed by Devoto. No relevant discrepancies between results obtained using these two approaches have been found, allowing the simplified method of Devoto to be still used in the computation of non-equilibrium transport properties like thermal conductivity, electrical conductivity and viscosity, with the exception of some diffusion coefficients. Results for composition, mass density, specific heat, thermal conductivity, electrical conductivity and viscosity of atmospheric pressure plasmas in the electron temperature range 300\u201340 000 K are reported

A three-dimensional investigation of the effects of excitation frequency and sheath gas mixing in an atmospheric-pressure inductively coupled plasma system

A three-dimensional numerical model for the simulation of the behaviour of a commercial inductively coupled plasma torch with non-axisymmetric reaction chamber has been developed, taking into account turbulence and gas mixing through RNG k\u2013epsilon theory and the combined diffusion approach of Murphy, respectively. The effects of changing coil current frequency, the hydrogen mixing in an argon primary gas and the flow patterns and temperature distributions which take place in a reaction chamber with a lateral gas outlet system and two observation windows have been investigated, with the final aim of setting up a computational tool able to predict the main features of plasma assisted treating and processing of injected raw materials. Three-dimensional shapes of the temperature, velocity and mass fraction fields have been obtained and analysed for an Ar\u2013H2 mixture at atmospheric pressure. Computations have been performed with two different coil current frequencies, i.e. 3 and 13.56 MHz, showing that for the lower value the 3D effects in the discharge are enhanced. Accurate mixing and demixing mechanisms have been investigated in both cases, including considerations on the relative importance of different thermal diffusion contributions due to mole fraction and temperature gradients. Temperature distributions in the reaction chamber for different cases have been correlated with different flow patterns and recirculation flows which take place as a consequence of the non-axisymmetry of the reaction chamber

Thermodynamic and transport pro­perties of Argon, Oxygen and Nitrogen atmospheric pressure thermal pla­smas in non-equilibrium

Thermal plasma processes and devices have been extensively studied and designed using modeling approach in the last two decades. Still, knowledge of thermodynamic and transport properties is one of the major needs in the modeling of thermal plasma processes. Computation of these properties is usually carried out through the approximated solution of the Boltzmann’s equation using the Chapman–Enskog’s method. While local thermodynamic equilibrium (LTE) was assumed in the past calculations, the development and use of more sophisticated plasma diagnostics have shown that this assumption often fails in thermal plasmas: for thermal non-equilibrium plasmas, the kinetic electron temperature Te is then assumed to be different from that of heavy species Th, chemical equilibrium being achieved. Nonequilibrium thermodynamic and transport property calculations of argon, nitrogen and oxygen plasmas at atmospheric pressure for electron temperature up to 45,000 K are here presented. Transport properties have been obtained using numerical codes developed by the authors which implement the Devoto’s electron and heavy particles decoupling approach. Variation of composition, specific volume, specific enthalpy, specific heat, thermal conductivity, electrical conductivity and viscosity as a function of electron temperature and different degrees of non-equilibrium are reported. Results are compared with available data from published reports to check the accuracy of the developed codes