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An appropriate coupling of an arc plasma column in the state of local thermodynamic equilibrium to a refractory cathode necessarily involves the non-equilibrium boundary layer between them. A model has been developed that combines a model of an equilibrium direct current arc plasma in atmospheric pressure argon with the assembly of a cathode made of tungsten and the boundary layer. A bidirectional coupling has been realized that allows us to consider a variable voltage drop across the boundary layer for different positions on the cathode. The results are obtained for arc currents between 10 and 150 A in the cases of both a unidirectional and a bidirectional coupling. The results show differences in the distributions of the temperature and the normal current density on the cathode surface and the radial and axial distributions of the plasma temperature. Comparison with the results of a fully non-equilibrium model of the arc plasma and experimental findings from optical emission spectroscopy shows a fair agreement for currents, where the deviations from equilibrium in the arc column can be ignored. For arc currents beyond 100 A, the arc attachment on the cathode appears in two forms, which differ from each other in the distributions of the temperature and the normal current density on the cathode surface, whereas the values of the total arc voltage are close to each other. [ABSTRACT FROM AUTHOR]

Focuses on a study which investigated the start-up phase of a mercury high-pressure discharge. Findings from the electrical and spectroscopic measurements of a steady-state discharge; Description of the evolution of the electric field and the voltage drop at the electrodes; Implications of the excitation temperature results for mercury and argon.

This paper deals with the modelling of the convection processes in metal-halide lamp discharges (HgDyI3). For this, we realized a 3D model, a steady, direct current powered and time-depending model for the solution of conservation equations relative to mass, momentum, and energy. After validation, this model was applied to the study of the effect of some parameters that have appeared on major transport phenomena of mass and energy in studying the lamp. Indeed, the electric current, the atomic ratio (Hg/Dy), and the effect of the convective transport have been studied. [ABSTRACT FROM AUTHOR]

This work is devoted to the calculation of the chemical composition and transport coefficients of HgDyI3 plasmas in thermal equilibrium. These calculations are performed for pressures equal to 2MP and for temperatures varying from 1000 to 10 000 K. The thermal and electrical conductivity as well as viscosity have been computed as a function of temperature at different atomic ratios. The computational method proposed by Devoto from the classical formalism described by Hirschfelder et al. [Molecular Theory of Gases and Liquids (John Wiley and Sons, New York, 1954)] is used. [ABSTRACT FROM AUTHOR]

This article presents the results of a numerical study on natural convection in a square enclosure filled with ethylene glycol–copper nanofluid in the presence of magnetic fields. Two opposite horizontal walls of the enclosure are insulated and the two vertical walls are kept constant at different temperatures. A uniform horizontal magnetic field is externally imposed. The governing equations (mass, momentum, and energy) are formulated and solved numerically with a finite element using COMSOL Multiphysics. The effects of pertinent parameters such as Rayleigh number (103 ≤ Ra ≤ 107), Hartmann number (0 ≤ Ha ≤ 120), and solid volume fraction (0 ≤ φ ≤ 0.06) on the flow and the heat transfer performance of the enclosure are examined when the Prandtl number is assumed to bePr = 151. [ABSTRACT FROM AUTHOR]

An optimization method based on a physical analysis of the temperature profile and different terms in the radiative transfer equation is developed to reduce the time computation of the net emission. This method has been applied for the cylindrical discharge in sodium vapor. Numerical results show a relative error of spectral flux density values lower than 5% with an exact solution, whereas the computation time is about 10 orders of magnitude less. This method is followed by a spectral method based on the rearrangement of the lines profile. Results are shown for Lorentzian profile and they demonstrated a relative error lower than 10% with the reference method and gain in computation time about 20 orders of magnitude. [ABSTRACT FROM AUTHOR]

This paper is devoted to study the dynamics of a discharge lamp with high intensity in a horizontal position. As an example of application, we chose the high-pressure mercury lamp. For this, we realized a three-dimensional model, a stable and powered DC. After the validation of this model, we used it to reproduce the influence of some parameters that have appeared on major transport phenomena of mass and energy in studying the lamp operating in a horizontal position. Indeed, the mass of mercury and the electric current are modified and the effect of convective transport is studied. [ABSTRACT FROM AUTHOR]

We present in this paper a comparison between results obtained with a laminar and turbulent models for high-pressure mercury arc. The two models are based on the resolution of bidimensional time-dependent equations by a semi-implicit finite-element code. The numerical computation of turbulent model is solved with large eddy simulation model; this approach takes into account the various scales of turbulence by a filtering method on each scale. The results show the quantitative influence of turbulence on the flow fields and also the difference between laminar and turbulent effects on the dynamic thermal behaviour and on the characteristics of the discharge. [ABSTRACT FROM AUTHOR]

This paper discusses the thermal behavior of a high pressure mercury lamp in a horizontal position, compared with that of a vertical lamp. The model adopted is three-dimensional, steady, and powered DC. After the model validation, we analyzed temperature fields and velocities for the case of the lamp in a horizontal position by comparing it with those of a lamp in vertical position. This setting initially fixed the wall temperature equal to 1000 K. However, the morphology of the temperature profile in the case of the horizontal lamp indicates that the temperature of the wall cannot be uniform. Thus, we have, in a second time, performed an energy balance at the wall to calculate its temperature. This aims to understand the influence of convection on the thermal properties of the source. [ABSTRACT FROM AUTHOR]

In this article we will discuss, in detail, the results obtained for a simple geometry of discharge (two-dimensional stationary or one-dimensional non stationary). It aims to give an idea about the discharge properties that emerge from the interaction of various physical processes. By using a variation of the fundamental parameters, we can show the capacity of the model to reproduce all the macroscopic properties of plasma discharge in sodium vapor. The validation of the model will be discussed and some comparisons with the existing experimental data will be presented. [ABSTRACT FROM AUTHOR]

Modern high-pressure discharge lamps are forced to provide instant light and hot relight capabilities-if possible at lower power units. A detailed understanding of the warm-up of high-pressure discharge lamps is therefore required. Complex fluid model codes were developed for the past years including more and more processes like two-dimensional treatment of convection trying to provide a more comprehensive and consistent description of high-pressure discharge lamps. However, there is a lack of experimental data to examine the performance of these models. This work provides a very complete set of geometrical, electrical, spectroscopic, and thermographic data according to the warm-up of a high-pressure mercury discharge lamp that is compared to the results of a state of the art fluid code. Quantitative agreement is achieved for single parameters like wall temperatures. But the paper also reveals the need for further investigations and improvements of the code. [ABSTRACT FROM AUTHOR]

The main objective of this work is to provide a better understanding of the warm-up phase of high-intensity discharge lamps. As an example of application, we chose the high-pressure mercury lamp. Based on two-dimensional fluid model parameters, such as the electric current, the length and the diameter of the burner are modified and the effect of the convective transport is studied. This allows us to obtain a thorough understanding of the physics of these lamps in their transitory phase. The simulation of the warm-up phase is a must for the proper predictions of the lamp behavior and can be conducted by solving the energy balance, momentum, and Laplace’s equations for the plasma, using the frame of the local thermodynamic equilibrium coupled with the energy balance of the wall. [ABSTRACT FROM AUTHOR]

A time-dependent two-dimensional computational fluid model has been adopted to investigate the dynamic behavior of the high-pressure mercury lamp during the last phase of the warm-up period. The model solves the combined momentum, continuity, energy, and electric field equations for the plasma and the energy equation for the wall. Two models have been compared. The first takes convection into account and is called “convection model.” The second, which neglects this term, is termed “convectionless model.” Good agreement between the predictions and experimental data from literature has been obtained. It is found that the convection affects the lamp performance by increasing the mercury losses behind the electrodes and the mercury-evaporation time. [ABSTRACT FROM AUTHOR]

In this paper, a second-order continuum model for radio-frequency glow discharge plasma between parallel-plate electrodes is presented. Simulations have been performed for discharges in argon and O 2 . The basic data needed for different collision processes are explicitly given with a high degree of accuracy. These data are rigorously calculated by using a multiterm Boltzmann equation solution for electrons and a Monte Carlo simulation technique for ions. The specificity of the present work is the use of a second-order fluid model solved by using a powerful finite-element scheme associated with basic data rigorously calculated. Detailed results for two types of discharge are presented and contrasted. The phenomena associated with the transition of the discharge into different operating regimes at relatively low and high pressures are demonstrated and discussed. [ABSTRACT FROM AUTHOR]

The main purpose of the present work consists in the study of supply frequency and sodium vapor pressure effects on the sodium lamp properties. The retained model is a two-temperature channel type that reproduces quite well the electrical and thermal behaviors as well as the main radiative characteristics of mercury-sodium discharge plasma and can be easily coupled with the lamp circuitry software. [ABSTRACT FROM AUTHOR]

This paper presents a numerical study of the dynamic behavior of high-pressure mercury discharge lamp as a function of supply mode. Bidimensional time-dependent equations have been solved by using a semi-implicit finite-element code. The model has been developed in the frame of the local thermodynamic equilibrium hypothesis. After validation by using experimental data from the literature, this model was applied to analyze the effects of some key parameters such as frequency for an ac arc current and the ratio cycle parameter for square arc-current wave form on the convective process. The results obtained have been used to analyze the dynamic thermal behavior of high-pressure mercury plasma (pressure equal to 0.3 MPa) working under currents widely different in frequency and wave form. [ABSTRACT FROM AUTHOR]

A LTE chemical model is developed to determine the plasma composition and transport coefficients of a thallium iodide discharge. Collision integrals, diffusion coefficients, thermal and electrical conductivity as well as conductance have been computed as functions of temperature at different atomic ratios using the Chapman Enskog theory. This chemical model is then coupled with a one-dimensional time-dependent fluid model to describe the temperature variation and electrical behaviour of the lamp. [ABSTRACT FROM AUTHOR]

Thermography is an established experimental method to measure wall temperatures of high-pressure discharge lamps resulting in 2-D images. However, theoretical models, including the heat balance of the tube wall, are usually based on a cylinder symmetric 2-D model, where the tube wall surface is represented by a 1-D line. In this paper, a comparison between experimental and theoretical results are presented, where a 2-D thermographic image is reconstructed from the model calculations. This allows visualizing and discussing of some capabilities and limitations of the theoretical model. [ABSTRACT FROM AUTHOR]

The aim of this work is to study the local thermodynamic equilibrium (LTE) deviations in arc discharges plasma generated in high-intensity discharge lamps operating under an ac (50 Hz) power supply. To achieve this goal, we elaborate a two-temperature, two-dimensional, and time-depending model. We have found numerical results almost reproducing the experimental data, which allows us to validate this model. After validation, we have discussed different energy term effects on the LTE deviations. [ABSTRACT FROM AUTHOR]

This paper deals with the modelling of the convection processes in metal-halide lamp discharges (HgDyI3). For this, we realized a 3D model, a steady, direct current powered and time-depending model for the solution of conservation equations relative to mass, momentum, and energy. After validation, this model was applied to the study of the effect of some parameters that have appeared on major transport phenomena of mass and energy in studying the lamp. Indeed, the electric current, the atomic ratio (Hg/Dy), and the effect of the convective transport have been studied. [ABSTRACT FROM AUTHOR]

Abstract: The current study presents a numerical computation of combined gas radiation and forced convection through two parallel plates. A laminar flow of a temperature-dependent and non-grey gas in the entrance region of the channel was investigated. Over-heated water vapor was chosen as a gas because of its large absorption bands. Some special attention was given to entropy generation and its dependence on geometrical and thermodynamic parameters. The radiative part of the study was solved using the “Ray Tracing” method through S 4 directions, associated with the “statistical narrow band correlated-k” (SNBCK) model. The temperature fields were used to calculate the distributions of local and global entropy generation. [Copyright &y& Elsevier]

In this research, we studied the performance analysis of inductively coupled radiofrequency plasma "RF-ICP" torch used in multi-material processing. A 2D numerical model built with COMSOL Multiphysics was used to study the discharge behavior and evaluate the overall efficiency transmitted into the plasma system. The temperature and velocity flow of the plasma were investigated. The numerical results are consistent with previous experimental studies. The temperature and velocity profiles are represented under a wide range of RF power and for different sheath gas flow rates. With increasing power, the radial peak temperature typically shifts towards the wall. The resistance of the torch rises whereas the inductance diminishes with increasing RF power. The overall dependency of the coupling efficiency to the RF power is also estimated. The stabilization of the plasma flow dependency to the sheath swirl flow was investigated. The incorporation of Helium (0.02%) into an Argon gas was established to minimize the energy lost in the sidewall. The number and spacing of induction coil numbers affects the temperature and flow field distribution. A valuable approach to designing and optimizing the induction plasma system is presented in the proposed study. The obtained results are fundamental to specify ICP torch design criteria needed for multi-material processing.

A three-dimensional numerical modelling of a time-dependent, turbulent thermal plasma jet was developed to synthetize silicon nanopowder. Computational fluid dynamics and particle models were employed via COMSOL Multiphysics ® v. 5.4 (COMSOL AB, Stockholm, Sweden) to simulate fluid and particle motion in the plasma jet, as well as the heat dependency. Plasma flow and particle interactions were exemplified in terms of momentum, energy, and turbulence flow. The transport of nanoparticles through convection, diffusion, and thermophoresis were also considered. The trajectories and heat transfer of both plasma jet fields, and particles are represented. The swirling flow controls the plasma jet and highly affects the dispersion of the nanoparticles. We demonstrate a decrease in both particles' velocity and temperature distribution at a higher carrier gas injection velocity. The increase in the particle size and number affects the momentum transfer, turbulence modulation, and energy of particles, and also reduces plasma jet parameters. On the other hand, the upstream flame significantly impacts the particle's behavior under velocity and heat transfer variation. Our findings open the door for examining thermal plasma impact in nanoparticle synthesis, where it plays a major role in optimizing the growth parameters, ensuring high quality with a low-cost technique.