Andrea Mentrelli

Three-dimensional modeling of inductively coupled plasma torches*

A 3D model for the simulation of inductively coupled plasma torches (ICPTs) working at atmospheric pressure is presented, using a customized version of the computational fluid dynamics (CFD) commercial code FLUENT®. The induction coil is taken into account in its actual 3D shape, showing the effects on the plasma discharge of removing the axisymmetric hypothesis of simplification, which characterizes 2D approaches. Steady flow and energy equations are solved for optically thin argon plasmas under the assumptions of local thermodynamic equilibrium (LTE) and laminar flow. The electromagnetic field equations are solved on an extended grid in the vector potential form. In order to evaluate the importance of various 3D effects on calculated plasma temperature and velocity fields, comparisons of our new results with the ones obtainable from 2D models and from an improved 2D model that includes 3D coil effects are presented. 3D results are shown for torches working under various geometric and operating conditions and with different coil shapes, including conventional helicoidal, as well as planar, elliptical, and double-stage configurations.

3-D numerical analysis of powder injection in inductively coupled plasma torches

Numerical simulations of the trajectory and thermal history of spherical particles injected into inductively coupled plasma torches working at atmospheric pressure have been performed taking into account the effects of coupling between particles and plasma and the turbulent dispersion of the particles, in the frame of a stochastic approach. The computational domain includes the torch region, as well as a region downstream the torch representing a reaction chamber.

3-D turbulent modeling of an ICPT with detailed gas injection section

A three-dimensional FLUENT-based turbulent model is developed to simulate the physical behavior of an inductively coupled plasma torch working at atmospheric pressure and reproducing the actual geometry of the commercial Tekna Plasma Systems Inc. PL-35. Particular attention has been focused on the detailed modeling of the inlet gas section region, showing its effects on the predicted argon plasma temperature and velocity fields.

Three-dimensional time-dependent modeling of magnetically deflected transferred arc

A numerical FLUENT-based model has been developed for the three-dimensional and time-dependent simulation of a magnetically deflected transferred arc. Results are presented for a case in which an argon arc is deflected with a 150-A current flowing in a wire parallel to the axis of the arc.

Turbulence and fire-spotting effects into wild-land fire simulators

Abstract This paper presents a mathematical approach to model the effects and the role of phenomena with random nature such as turbulence and fire-spotting into the existing wildfire simulators. The formulation proposes that the propagation of the fire-front is the sum of a drifting component (obtained from an existing wildfire simulator without turbulence and fire-spotting) and a random fluctuating component. The modelling of the random effects is embodied in a probability density function accounting for the fluctuations around the fire perimeter which is given by the drifting component. In past, this formulation has been applied to include these random effects into a wildfire simulator based on an Eulerian moving interface method, namely the Level Set Method (LSM), but in this paper the same formulation is adapted for a wildfire simulator based on a Lagrangian front tracking technique, namely the Discrete Event System Specification (DEVS). The main highlight of the present study is the comparison of the performance of a Lagrangian and an Eulerian moving interface method when applied to wild-land fire propagation. Simple idealised numerical experiments are used to investigate the potential applicability of the proposed formulation to DEVS and to compare its behaviour with respect to the LSM. The results show that DEVS based wildfire propagation model qualitatively improves its performance (e.g., reproducing flank and back fire, increase in fire spread due to pre-heating of the fuel by hot air and firebrands, fire propagation across no fuel zones, secondary fire generation, ...) when random effects are included according to the present formulation. The performance of DEVS and LSM based wildfire models is comparable and the only differences which arise among the two are due to the differences in the geometrical construction of the direction of propagation. Though the results presented here are devoid of any validation exercise and provide only a proof of concept, they show a strong inclination towards an intended operational use. The existing LSM or DEVS based operational simulators like WRF-SFIRE and ForeFire respectively can serve as an ideal basis for the same.

Three dimensional modelling of inductively coupled plasma torches: comparison with experiments and applications

A three-dimensional model for the simulation of inductively coupled plasma torches working at atmospheric pressure has been developed, using the customized computational fluid dynamic (CFD) commercial code FLUENT. The helicoidal coil is taken into account in its actual 3-D shape, showing its effects on the plasma discharge for various geometric, electric and operating conditions without axisymmetric hypotheses of simplification. The electromagnetic equations are solved in their vector potential form, while the steady flow and energy equations are solved for optically thin argon plasmas under the assumptions of LTE and laminar flow. In order to evaluate the importance of various 3-D effects on calculated plasma temperature and flow fields, comparisons of our results with the ones obtainable from 2-D models and from an improved 2-D model that includes 3-D coil effects are presented. The effects of changing inlet gas flow rates, direction of the swirl velocity component, axial length and number of turns of the coil and the net amount of power dissipated in the discharge are evidenced, in order to give useful hints for avoiding the formation of a hot temperature spot in the confinement tube wall due to the axial displacement of the plasma fireball. Three-dimensional results concerning different coil shapes are presented. Calculations have also been carried out for some real torches specifically designed for particular applications, with the aim of validating the code. In addition, an improved version of the 3-D model has been used to simulate thermal history and trajectory of metallic and ceramic powders injected in the discharge through a carrier gas, taking into account the plasma-particle interaction. Moreover, comparisons of calculated side-on emission intensity profiles obtained from 3-D temperature results with experimental data coming from optical emission spectroscopy measurements have been carried out, for a 300 W, 40 MHz argon radio frequency inductively coupled plasma operated at atmospheric pressure, for some characteristic Ar-I wavelengths.

The Randomized Level Set Method and an Associated Reaction-Diffusion Equation to Model Wildland Fire Propagation

Front propagation can be studied by two alternative approaches: the level set method and the reaction-diffusion equation. When a front propagates in a random environment it gets a random character and these two approaches can indeed be considered complementary and reconciled. In fact, if the level set contour is randomized accordingly to the probability density function of the front particle displacement, the resulting averaged process emerges to be governed by an evolution equation of the reaction-diffusion type. This approach turns out to be useful to simulate random effects in wildland fire propagation as those due to turbulent heat convection and fire spotting phenomena.

Shock and rarefaction waves in a hyperbolic model of incompressible materials

The aim of the present paper is to investigate shock and rarefaction waves in a hyperbolic model of incompressible materials. To this aim, we use the so-called extended quasi-thermal-incompressible (EQTI) model, recently proposed by Gouin & Ruggeri (H. Gouin, T. Ruggeri, Internat. J. Non-Linear Mech. 47 688–693 (2012)). In particular, we use as constitutive equation a variant of the well-known Bousinnesq approximation in which the specific volume depends not only on the temperature but also on the pressure. The limit case of ideal incompressibility, namely when the thermal expansion coefficient and the compressibility factor vanish, is also considered.

3-D Modeling of DC Transferred Arc Twin Torch for Asbestos Inertization

Summary form only given. The aim of this work is to investigate by means of a 3-D numerical model the fluid flow and temperature distribution of a plasma transferred electric arc discharge generated between two suspended metallic electrodes. This twin torch device is used inside a plasma furnace for hazardous waste incineration and asbestos inertization. Flow and energy equations are solved for an optically thin Ar plasma under conditions of LTE, while the electromagnetic field equations are solved in their scalar and vector potential form. Electrodes interfaces are taken into account using a simplified approach, imposing a current density distribution on the cathode surface. The anode and cathode regions are discretized in their detailed design, in order to better understand the effects of their geometries on the discharge behavior. Turbulence effects are taken into account into the model using a RANS approach, as well as the effect on the discharge characteristics of using different types of plasma gas (air and Ar/H2 mixtures), for various geometric and operating conditions. Results are presented in order to characterize the fluid flow and the temperature field of this kind of device. Unsteady effects that may arise under particular operating conditions in the zone of attachment of the two plasma columns are investigated by means of a time dependent approach, in order to select operating conditions and the relative geometric configuration of the two metallic electrodes that induce a stable plasma configuration in the downstream zone of attachment of the two plasma columns. Simulations can also give important information on non-axisymmetric anode attachment under particular operating conditions. Simulations are performed using a customized CFD commercial code FLUENTcopy, parallelized over a network cluster of double processor calculators in order to use the full capabilities of the 3-D modelling code. Conclusions will be drawn concerning the possibility of using this modelling tool to predict the plasma discharge behaviour when anode disruption occurs under critical operating conditions as an effect of gas entrainment in the anode region

3-D Turbulent Modeling of an ICPT with Detailed Gas Injection Section

A three-dimensional FLUENT-based turbulent model is developed to simulate the physical behavior of an inductively coupled plasma torch working at atmospheric pressure and reproducing the actual geometry of the commercial Tekna Plasma Systems Inc. PL-35. Particular attention has been focused on the detailed modeling of the inlet gas section region, showing its effects on the predicted argon plasma temperature and velocity fields.