IRIS Università degli Studi di Bolognahttps://cris.unibo.itIl sistema di repository digitale IRIS acquisisce, archivia, indicizza, conserva e rende accessibili prodotti digitali della ricerca.Sun, 01 Aug 2021 01:25:50 GMT2021-08-01T01:25:50Z10671- Three-Dimensional Modeling of Thermal Plasmas (RF and Transferred Arc) for the Design of Sources and Industrial Processeshttp://hdl.handle.net/11585/52241Titolo: Three-Dimensional Modeling of Thermal Plasmas (RF and Transferred Arc) for the Design of Sources and Industrial Processes
Abstract: A three-dimensional model for the simulation of inductively coupled plasma torches (ICPTs) working at
atmospheric pressure has been developed at the University of Bologna, using customized CFD
commercial code FLUENT [1-3]. 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 plasmas
under the assumptions of LTE and laminar flow [3-4]. Simulations have been performed for Ar and
Ar/H2 plasmas, treating, in the latter case, diffusion as suggested in [5] and making use of transport and
thermodynamic coefficient published in [6]. In order to evaluate the importance of various 3-D effects
on calculated plasma temperature and flow fields, comparisons of our new results with the ones
obtainable from 2-D models and from an improved 2-D model that includes 3-D coil effects [4] are
presented. In addition, the gas injection section of an industrial TEKNA PL-35 plasma torch is included
in the model without geometry simplifications, refining the mesh at the injection points, in order to
perform a more realistic simulation of the inlet region of the discharge, taking into account turbulence
effects using the Reynolds Stress Model [7]. 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 including planar coil configuration are also
presented. Metallic and ceramic particle axial injection in the discharge through a carrier gas by means
of a probe is simulated as well, taking into account the energy and momentum transfer between the
continuous and the discrete phase [8] and the effect of particle turbulent dispersion [9, 10]. In order to
test the numerical codes, 3-D simulation results for an existing torch [11] designed for applications in
atmospheric plasma spraying of materials, are compared with the experimental measurements carried
out in [11] by means of an enthalpy probe technique. Moreover, results coming from 3-D modeling
concerning a torch configuration designed and realized for plasma assisted chemical synthesis and
deposition of pure silica [12, 13], are presented. In addition, temperature results from 3-D numerical
simulation of a 0.3 kW, 40 MHz argon radio frequency inductively coupled plasma operated at
atmospheric pressure are used to reconstruct side-on emission intensity profiles for some characteristic
Ar-I wavelengths, and than compared with the ones obtained from direct emission spectroscopy
measurements [14].
The behavior transferred arc thermal plasma sources operating at atmospheric pressure for the treatment
of a substrate material (for waste treatment purposes and for metallic substrate cutting or hardening)
[15-19] is also investigated by means of a 3-D time-dependent numerical model, using a customized
version of the CFD commercial code FLUENT©. Unsteady flow and heat transfer equations are solved
with coupled electromagnetic ones, for an Ar optically thin plasma under conditions of laminar flow and
LTE. The transient effects of an imposed external magnetic field [16, 17] on the shape of the single
torch arc are investigated. The importance of fully investigating plasma velocity and temperature fields
in high power twin torch transferred arc systems designed for waste treatment purposes is outlined with
reference to a plasma source designed and operated by Centro Sviluppo Materiali (CSM S.p.A.) in
C...
Mon, 01 Jan 2007 00:00:00 GMThttp://hdl.handle.net/11585/522412007-01-01T00:00:00Z
- Three-Dimensional Time-Dependent Modeling of Magnetically Deflected Transferred Archttp://hdl.handle.net/11585/19316Titolo: Three-Dimensional Time-Dependent Modeling of Magnetically Deflected Transferred Arc
Abstract: 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.
Sat, 01 Jan 2005 00:00:00 GMThttp://hdl.handle.net/11585/193162005-01-01T00:00:00Z
- Molecular extended thermodynamics of rarefied polyatomic gases and wave velocities for increasing number of momentshttp://hdl.handle.net/11585/302515Titolo: Molecular extended thermodynamics of rarefied polyatomic gases and wave velocities for increasing number of moments
Abstract: Molecular extended thermodynamics of rarefied polyatomic gases is characterized by two hierarchies of equations for moments of a suitable distribution function in which the internal degrees of freedom of a molecule is taken into account. On the basis of physical relevance the truncation orders of the two hierarchies are proven to be not independent on each other, and the closure procedures based on the maximum entropy principle (MEP) and on the entropy principle (EP) are proven to be equivalent. The characteristic velocities of the emerging hyperbolic system of differential equations are compared to those obtained for monatomic gases and the lower bound estimate for the maximum equilibrium characteristic velocity established for monatomic gases (characterized by only one hierarchy for moments with truncation order of moments N) by Boillat and Ruggeri (1997)
$\frac{\lambda^{E, max}_{(N)}}{c_0} \geq \sqrt{\frac{6}{5}\left(N-\frac{1}{2}\right)}$, ($c_0 = \sqrt{\frac{5kT}{3m}}$)
is proven to hold also for rarefied polyatomic gases independently from the degrees of freedom of a molecule.
Wed, 01 Jan 2014 00:00:00 GMThttp://hdl.handle.net/11585/3025152014-01-01T00:00:00Z
- The Propagation of Shock Waves in Incompressible Fluids: The Case of Freshwaterhttp://hdl.handle.net/11585/305164Titolo: The Propagation of Shock Waves in Incompressible Fluids: The Case of Freshwater
Abstract: In this paper we investigate the basic features of shock waves propagation in freshwater in the framework of a hyperbolic model consisting of the one-dimensional Euler equations closed by means of polynomial equations of state extracted from experimental tabulated data available in the literature (Sun et al. in Deep-Sea Res. I 55:1304-1310, 2008). The Rankine-Hugoniot equations are numerically solved in order to determine the Hugoniot locus representing the set of perturbed states that can be connected through a k-shock to an unperturbed state.
The results are found to be consistent with those previously obtained in the framework of the EQTI model by means of a modified Boussinesq equation of state.
Wed, 01 Jan 2014 00:00:00 GMThttp://hdl.handle.net/11585/3051642014-01-01T00:00:00Z
- Modelling wildland fire propagation by tracking random frontshttp://hdl.handle.net/11585/302514Titolo: Modelling wildland fire propagation by tracking random fronts
Abstract: Wildland fire propagation is studied in literature by two alternative approaches, namely the reaction-diffusion equation and the level-set method. These two approaches are considered alternative each other because the solution of the reaction-diffusion equation is generally a~continuous smooth function that has an exponential decay and an infinite support, while the level-set method, which is a front tracking technique, generates a sharp function with a finite support. However, these two approaches can indeed be considered complementary and reconciled. Turbulent hot-air transport and fire spotting are phenomena with a random character that are extremely important in wildland fire propagation. As a consequence the fire front gets a random character, too. Hence a tracking method for random fronts is needed. In particular, the level-set contourn is here randomized accordingly to the probability density function of the interface particle displacement. Actually, when the level-set method is developed for tracking afront interface with a random motion, the resulting averaged process emerges to be governed by an
evolution equation of the reaction-diffusion type. In this reconciled approach, the rate of spread of the fire keeps the same key and characterizing role proper to the level-set approach. The resulting model emerges to be suitable to simulate effects due to turbulent convection as fire flank and backing fire, the faster fire spread because of the actions by hot air pre-heating and by ember landing, and also the fire overcoming a firebreak zone that is a~case not resolved by models based on the level-set method. Moreover, from the proposed formulation it follows a correction for the rate of spread formula due to the mean jump-length of firebrands in the downwind direction for the leeward sector of the fireline contour.
Tue, 01 Jan 2013 00:00:00 GMThttp://hdl.handle.net/11585/3025142013-01-01T00:00:00Z
- Numerical simulation for the characterization of operating conditions of RF–RF hybrid plasma torcheshttp://hdl.handle.net/11585/19275Titolo: Numerical simulation for the characterization of operating conditions of RF–RF hybrid plasma torches
Abstract: A two-dimensional (r, z) numerical code has been developed to investigate the prominent features of RF–RF hybrid plasma torches with two stages of different diameter. Flow and temperature fields have been calculated within the assumptions of laminar flow and local thermodynamic equilibrium for the optically thin argon plasma operated at atmospheric pressure, taking into full account the electromagnetic interaction between the primary and the secondary stage of the hybrid device. Results from a detailed parametric study for various geometric, gas flow and electric configurations aim at putting into evidence the wide range of operating conditions that can characterize the use of RF–RF hybrid plasma torches for industrial applications, showing also their possibility to give high enthalpy plasma jets with high torch efficiencies. The magnetofluidynamic modelling described in this work can be an effective tool for providing the theoretical framework for a deep understanding of RF–RF hybrid plasma torches and for designing them as suitable sources for chemical processing of materials, when utilized within an integrated approach that would match the induction plasma torch simulation with the RF generator operating conditions to evaluate the total source efficiency for each particular hybrid configuration.
Thu, 01 Jan 2004 00:00:00 GMThttp://hdl.handle.net/11585/192752004-01-01T00:00:00Z
- 3-D Modelling of DC Transferred Arc Twin Torch for Asbestos Inertizationhttp://hdl.handle.net/11585/20047Titolo: 3-D Modelling of DC Transferred Arc Twin Torch for Asbestos Inertization
Abstract: 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 nonaxisymmetric anode attachment under particular operating conditions. Simulations are performed using a customized CFD commercial code FLUENT©, 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.
Sat, 01 Jan 2005 00:00:00 GMThttp://hdl.handle.net/11585/200472005-01-01T00:00:00Z
- Shock structure in extended thermodynamics with second-order maximum entropy principle closurehttp://hdl.handle.net/11585/786063Titolo: Shock structure in extended thermodynamics with second-order maximum entropy principle closure
Fri, 01 Jan 2021 00:00:00 GMThttp://hdl.handle.net/11585/7860632021-01-01T00:00:00Z
- Shock structure in the 14 moment system of extended thermodynamics with high order closure based on the maximum entropy principlehttp://hdl.handle.net/11585/785495Titolo: Shock structure in the 14 moment system of extended thermodynamics with high order closure based on the maximum entropy principle
Wed, 01 Jan 2020 00:00:00 GMThttp://hdl.handle.net/11585/7854952020-01-01T00:00:00Z
- On two-Pulse and Shock Evolution in a Class of Ideally Hard Elastic Materialshttp://hdl.handle.net/11585/36117Titolo: On two-Pulse and Shock Evolution in a Class of Ideally Hard Elastic Materials
Abstract: Pulse and shock interaction is investigated for a class of ideally hard elastic materials. The latter admit the soliton-like property that disturbances emerge asymptotically unaltered in shape and speed following the interaction process.
Mon, 01 Jan 2007 00:00:00 GMThttp://hdl.handle.net/11585/361172007-01-01T00:00:00Z