Bernard Pateyron

Numerical simulation of hydroxyapatite powder behaviour in plasma jet

The paper deals with numerical simulation of hydroxyapatite (HA) coating deposition by plasma spraying. The velocity and temperature fields of ArqN plasma generated by a commercial plasma torch of given power at atmospheric pressure are 2 calculated in three-dimensional with the use of GENMIX numerical code. The HA powder particles granulometry and internal morphology were characterized with the use of laser sizer and scanning electron microscope, respectively. The image analysis enabled to determine the internal porosity of powder particles manufactured by the spray-drying method. The physical and thermophysical data of HA as a function of temperature were collected from literature sources. The HA particles injection velocity into the plasma jet was calculated analytically. The trajectories and temperatures fields inside these particles were calculated numerically using Plasma 2000 code. These fields determined at experimental spray distance, were used to predict the crystal phases composition of the sprayed coating. � 2003 Elsevier B.V. All rights reserved.

Thermodynamic and transport properties of Ar-H2 and Ar-He plasma gases used for spraying at atmospheric pressure. I: Properties of the mixtures

AbstractThe transport properties of argon/ helium and argon/hydrogen mixtures used (or] plasma spraying were calculated according to the Chapman-Enskog theory with the following approximations: third for electrical conductivity and for electron translational thermal conductivity, second for heavy species translational thermal conductivity and internal thermal conductivity, and first for reactional thermal conductivity and viscosity.The results are as follows:- for electrical conductivity for T < 14,000 K, that of ArIH2 is almost unaffected by the mole percent H2, while that of ArlHe is almost that of Ar up to 80 mole % He.- for viscosity, that of Ar-H2 is between those of pure Ar and pure H2, while for Ar-He mixtures an “anomalous” behavior is observed with higher values of the mixture viscosity compared to those of the components, in the temperature range 6000–10,000 K. Such behavior is due to the value of the Ar-He interaction potential proposed and experimentally verified by Aziz et al.nThe simplified mixing rule of Wilke must be used very cautiously especially for Ar-He where it predicts higher values for the mixture.The addition of hydrogen or helium to argon increases its thermal conductivity drastically. When considering the mean integrated thermal conductivity, the addition of hydrogen results in a step variation when dissociation occurs, while the increase is more regular when adding He.

Study of the dynamic and static behavior of de vortex plasma torches: Part II: Well-tye cathode

This work was devoted to the study of the dynamic and static behavior of de vortex plasma torch with a well-type cathode (power level below 100 kW). The dynamic behavior of the torch was characterized by the fulctuations of arc voltage and current, plasma jet radiation, and acoustic pressure. Characteristic frequencies of the arc root movement inside the torch were observed. By numerical simulation (with the numerical codeMelodie, it was shown that the position of the erosion diameter) of the axial velocity along the cathode channel near the wall. The static behavior of the torch was inverstigated for different cathode designs. The variations of voltage U with arc current I, gas flow rate G nature of the gas and cathode design were represented by semiempirical relationships established between dimensionless numbers. By dimensional analysis, the behavior of this torch was compared with that of two powerful torches: the Aerospatiale and the Plasma Energy Corporation torches.

SOUND VELOCITY IN DIFFERENT REACTING THERMAL PLASMA SYSTEMS

In most cases the energy dissipated in plasma jets used either,for heating or spraying is varied by changing the are current, the total gas floc+rate, and composition. However, when doing so, conditions are reached where the plasma jet may become supersonic. To predict such conditions or to characterize supersonic plasma jets the knowledge of the sound velocitya is mandatory The goal of this paper is to calculatea versus plasma forming gas composition, temperature, and pressure. Rigorous calculation would imply the knowledge of the chemical reaction kinetics, sound velocity depending strongly on this. Unfortunately such kinetics are generally lolknown for plasma jet floras and the only possibility is to determine the equilibrium sound velocitya calculated through the isentropic coefficient T. This coefficient has been calculated taking into account the dissociation and ionization reactions at equilibrium for temperatures ranging from 300 to 25,000 K and pressures between 0.1 and 1 Mpa for Ar, H2, He, Ar-He, Ar-H2, O2, N2, air, .steam, and methane.aγ often called the “frozen” sound velocity, was also calculated using γ (ratio of specific heats) instead of Γ.

La production des plasmas thermiques

Resume Cet article fait suite a une journee detudes organisee par la section Convection de la Societe Francaise des Thermiciens (SFT) sur le theme Transferts convectifs par les jets (Paris, 15 mars 1995).

A lattice Boltzmann-based investigation of powder in-flight characteristics during APS process, part I: modelling and validation

This study aims to investigate turbulent plasma flow over spheroidal particles using the lattice Boltzmann (LB) method. A double population model D2Q9-D2Q4 is employed to calculate the plasma velocity and temperature fields. Along with the calculation process a conversion procedure is made between the LB and the physical unit systems, so that thermo-physical properties variation is fully accounted for and the convergence is checked in physical space. The configuration domain and the boundary condition treatment are selected based on the most cited studies in order to illustrate a realistic situation. The jet morphology analysis gives credible results by comparison with commonly published works. A second Lagrangian model has been developed to investigate the plasma-particles exchange during its in-flight. The tracking of the μ-sized particles allows concluding that our results are in sufficient agreement with those of the Jets&Poudres code and that the LB method account well for plasma jet physics which affects directly the particles in-flights.

Simulation and Modeling of Turbulent Plasma Jet Based on Axisymetric LBGK Model

The coating of surfaces by plasma spraying is an important manufacturing process with many industrial applications. In the last several decades, numerical modeling of plasma spraying processes has met with considerable attention [1,2,3]. That is in order to well understand the complex phenomena the plasma spray involves, for economic constraints and to well predict the plasma-inflight-particles exchanges since this affects directly the coating formability and microstructure. This study deals with the investigation of plasma jets using an axisymmetric LB thermal model. Plasma jets have been very successful in many applications (such as spraying, cutting, welding,…). The excellent choice of high performance plasma gases and spraying materials has been the subject of several experimental and numerical efforts. An excellent choice will be the response of efficient numerical studies and the results of experimental tests. Plasma jets are high temperature flows (>8000K). Therefore, all diffusion parameters involved in conservation equations are temperature dependent. In the following, we present a plasma jet investigation in an axisymmetric LBM (Jian’s model [4]). In the context of our knowledge, it is the first attempt to tackle this field by using the LBM. Further reading on solution procedure, the model implementation and assumptions may be found in [5,6].

NUMERICAL SIMULATION OF THE MELTING OF PARTICLES INJECTED IN A PLASMA JET

This work presents the numerical simulation of the melting process of a particle injected in a plasma jet. The plasma process is nowadays applied to produce thin coatings on metal mechanical components with the aim of improving the surface resistance to different phenomena such as corrosion, temperature or wear. In this work we studied the heat transfer including phase-change of a bi-layer particle composed of a metallic iron core coated with ceramic alumina, inside a plasma jet. The model accounted for the environmental conditions along the particle path. The numerical simulation of this problem was performed via a temperature-based phase-change finite element formulation. The results obtained with this methodology satisfactorily described the melting process of the particle. Particularly, the results of the present work illustrate the phase change evolution in a bi-layer particle during its motion in the plasma jet. Moreover, the numerical trends agreed with those previously reported in the literature and computed with a finite volume enthalpy based formulation.

Numerical Study of Melting/Solidification by a Hybrid Method Coupling a Lattice Boltzmann and a Finite Volumes Approaches

In this paper, we propose a hybrid method coupling a Lattice Boltzmann Method (LBM) and a Finite Volume Method (FVM), to study melting and solidification problems. The LBM is used to determine the dynamics field while the FVM is applied to discretize the energy equation. This model is validated by comparison to available literature results concerning a square cavity heated without phase change then for the melting of Gallium in an enclosure commonly used as benchmark test case.

Lattice Boltzmann Simulations for Thermal Conductivity Estimation in Heterogeneous Materials

For simulating flows in a porous medium, a numerical tool based on the Lattice Boltzmann Method (LBM) is developed with regards to the classical D2Q9 model. A short description of this model is presented. This technique, applied to two-dimensional configurations, indicates its ability to simulate phenomena of heat and mass transfer. The numerical study is extended to estimate physical parameters that characterize porous materials, like the so-called Effective Thermal Conductivity (ETC) which is of our interest in this paper. Obtained results are compared with those which could be found analytically and by theoretical models. Finally, a porous medium is considered to find its ETC.