Kamel Charrada

Thermalization of the high pressure mercury lamp positive column during the warm-up phase

This work deals with the modeling of high pressure mercury lamp positive column thermalization. Because of the important pressure variation during the start-up phase, the discharge properties change fundamentally before the steady state is reached. For this reason the corresponding pressure range is split into three phases, namely the low pressure, intermediate and high pressure phases, in which interesting simplifications of the simulation can be obtained. A self-consistent collisional-radiative model is used to simulate the first phase. In the second, the model has been modified in order to include the significant reactions of this phase. Finally a LTE model describes the high pressure phase. Partial validation of the models are obtained from the study of the warm-up of a mercury lamp supplied under DC conditions. The results obtained are in good agreement with literature experimental data and, furthermore, allow the discussion of the validity limits for each model. >

Dynamic thermal and radiative behaviors of a high pressure sodium lamp plasma

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.

Effect of a pulsed power supply on the spectral and electrical characteristics of HID lamps

Results of spectral and photometric measurements are presented for pulsed power operated high intensity discharges (HIDs). This investigation is related to the application of a pulsed power supply for pile driving of HID lamps. Specifically, we are interested in controlling the spectral response radiation of visible and ultraviolet (UV) lines for tertiary treatment of water using UV radiation. Simulations based on a physical model of the lamps were conducted. These results relate to the radial temperature, line intensity and electrical properties (voltage, power and conductivity). Good agreement has been found between the results of the simulations and the experimental findings.

Spatio-temporal study of the deviations from thermal equilibrium in a high-pressure mercury plasma working under an ac power supply

This work deals with the study of deviations from thermal equilibrium in high-pressure mercury discharges operating in ac mode. A one-dimensional time-dependent fluid model assuming a non-equilibrium plasma (two-temperature code) has been developed. This code solves, self-consistently, the set of hydrodynamic equations describing the discharge plasma, coupled with an equation describing the power supply circuit. This code is based on a finite-element method and it has been optimized in order to keep CPU times realistic. Our calculations at an industrial 50 Hz frequency, validated by using experimental data from the literature, allow us the possibility to better understand the mechanisms that are responsible for deviations from thermal equilibrium within an ac cycle. Furthermore, a parametric study allows us to study in detail the influence of some key parameters, such as frequency and mercury load on those deviations.

Modeling the warm-up phase of a high-pressure-lamps lighting network

This work presents a study of the dynamic regime of a lamp-network interaction corresponding to the warm-up phase of a high-pressure mercury discharge lamp. The lamps behavior is described by a variable pressure model using the local thermodynamic equilibrium (LTE) concept. Indeed, this model covers the most interesting phase of the network dynamic regime, where discharge lamps appreciably impose their nonlinearity. We first analyze the electrical behavior of the discharge lamp in a single phase circuit, taking into account the ballast saturation. Then a micronetwork is studied and are show the influence of the discharges evolution on currents in phases and neutral conductors. Finally, from the results of the physical model, we set up a simple parametric modeling which reproduces the electrical behavior of the lamp during its warm-up phase. Such an approach can be useful for electrical engineers working on the discharge supply circuits at industrial frequency (50-60 Hz).

Numerical modelling of a HgTlI discharge lamp: transport coefficients and thermodynamic properties

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.

Simulation of Expansion of Thermal Shock and Pressure Waves Inducaed by a Streamer Dynamics in Positive DC Corona Discharges

This paper is devoted to the simulation of the thermal shock and the induced pressure-waves expansion, generated by a dc pin-to-plan corona discharge in the air at ambient temperatures and under atmospheric pressure. The positive dc voltage applied to the tip generates a monofilamentary streamer that crosses the gap from the tip toward the plan. The simulation models are based on the coupling of a 2-D dynamics streamer model with the hydrodynamics conservation equations of a compressible gas. The source term for the gas dynamics equations takes into account the fast-energy relaxation from excited molecules to the random thermal energy. The simulation shows that the streamers generate a thermal shock near the anodic tip, which induces high pressure gradients and finally the gas expansion. The thermal shock is located just in front of the anodic tip, where the injected energy density is the highest. After 0.3 μs, the mean gas temperature increases up to around 800 K in a small volume just in front of the anodic tip while the maximum temperature reaches 1200 K. In addition, two pressure waves, a spherical and a cylindrical one, are induced with a propagation velocity of 370 m s-1 i.e., close to the speed of sound in air.

A dynamic study of the warm-up phase of a high-pressure mercury lamp

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.

Discrete ordinates method in the analysis of the radiative transfer in high intensity discharge lamps

This paper deals with radiation transfer in cylindrical high pressure discharges for which local thermodynamic equilibrium can be assumed. An S?N approximation (a set of N discrete directions) of the discrete ordinates method is used to solve the radiative transfer equation. A summary of the basic equations and numerical formulations is given in order to calculate the spectral intensities and then to evaluate radiative flux and net emission coefficient. Also, the net emission coefficient is described by a semi-empirical formula which contains terms representing the generation and absorption of radiation. The results are presented for a typical high pressure mercury discharge commonly used as a light source.

A two-dimensional modeling of the warm-up phase of a high-pressure mercury discharge lamp

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 Laplaces equations for the plasma, using the frame of the local thermodynamic equilibrium coupled with the energy balance of the wall.