Analysis of the Plasma Discharge Phenomena for Ceramic Metal Halide Lamps Using Finite Element Method

Abstract

Metal halide (MH) lamps comes under the category of high intensity discharge (HID) lamps, which involves high intensity thermal plasma discharge phenomenon. In this paper we have considered ceramic MH lamps. The plasma discharge in MH lamps is different from other plasma discharge by the velocity of all the discharge obeys Maxwellian distribution, the excited energy states are occupied by Boltzmann distribution, and composition of the plasma can be derived from local chemical equilibrium. This paper explores the temperature distribution and the immediate effects towards the life of MH lamp. The temperature profile for the MH lamp is numerically investigated using WELSIM 2.0, considering the lamp plasma model mathematical equations. Since electrode plays a significant role, influencing MH lamp life, it becomes imperative to understand the electrodes. In this context, the energy balance equation is taken into consideration. The equations are solved using finite element method. The necessary boundary condition for solution of the equation is the plasma boundary layer for the cathode heat conduction. The analysis provides the temperature distribution inside the lamp for different electrode geometry. The solutions to the equations have been pictorially investigated for the lamp starting phenomena and E/N ratio. For HID lamps in general, the improvements in HID technology are all linked to the performance of the arc tube, and within that tube, the chemical reaction, the pressure, and the temperature of the reaction. Another feature in the case of MH lamps that is worth mentioning in the determination of lamp life is the ratio between electric field to gas number density. From the above, we can draw the following conclusion that the radiation transport mechanism of the HID lamps plays a pivotal role apart from other parameters influencing the lifetime of HID lamps. The paper envisages all these aspects using PDEs, the solutions of which provide an insightful understanding of the phenomena substantially.