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.
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.
This paper deals with radiation transfer in a cylindrical high pressure HgTℓI discharge for which local thermodynamic equilibrium can be assumed. The discrete ordinates method (DOM) is used to solve the radiative transfer equation. Calculations of concentration profiles of all species have been performed using a parabolic temperature profile and a constant mercury/thallium ratio throughout the discharge tube. The influence of thallium in HgTℓI discharges on the spectroscopic parameters such as the spectral intensity, the radiative flux and the net emission coefficient is studied. A comparison of the calculated thallium line shapes with the measured ones shows good agreement.
Net emission coefficients were calculated for a two-dimensional HID light source in accordance with the composition, the local temperature, and the radiation relative to the rest of the discharge which can be absorbed in the same volume of an element. All important line-broadening mechanisms were included, and the effects of emission and absorption on the net emission coefficient were accounted for on a line-by-line basis. Particular attention has been paid to the effect of pressure on the net emission of the 253.7 nm resonance line and the visible lines.
This paper shows the implementation of the Discrete Ordinates Method for handling radiation problems in High Intensity Discharge (HID) lamps. Therefore, we start with presenting this rigorous method for treatment of radiation transfer in a two-dimensional, axisymmetric HID lamp. Furthermore, the finite volume method is used for the spatial discretization of the Radiative Transfer Equation. The atom and electron densities were calculated using temperature profiles established by a 2D semi-implicit finite-element scheme for the solution of conservation equations relative to energy, momentum, and mass. Spectral intensities as a function of position and direction are first calculated, and then axial and radial radiative fluxes are evaluated as well as the net emission coefficient. The results are given for a HID mercury lamp on a line-by-line basis. A particular attention is paid on the 253.7 nm resonance and 546.1 nm green lines.
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