Modélisation numérique des processus physico-chimiques dans les milieux à haute température.

Abstract

The interior of an operating light source is a very hostile environment. In the familiar gas-filled incandescent lamps, large temperature gradients are present. The greatly different gas/solid boundary temperatures give rise to large temperature gradients in the near atmospheric pressure gas filling which, in turn, result in complex, buoyancy driven, recirculating flow patterns in the working gases. In this work a modeling investigation of an operating halogen lamp is described the halogen lamp was chosen to be the focus of the studies because it provided ready optical access to its axial, intra-coil regions, it allowed simple, accurate control of gas temperatures over a very wide range (300 K to more than 3,000 K) and the composition of its 5% HBr and 95% N2 cold-fill chemical dose responds in a significant and reversible manner to the changing conditions which result from changes in the filament temperature. High fidelity, Fluent 6 computational fluid dynamics (CFD) model of the lamp is created which included a sub-model to implement local Gibbs Energy minimization within the operating lamp. The finite volume method has been used to solve the equations of continuity, momentum (the Navier Stokes equations) and energy. The spatially precise knowledge of both physical conditions, and multispecies chemical composition, over a wide range of lamp operating conditions creates a unique and important opportunity to test and validate understanding of such complex systems through the use of computer based models. The model predictions were critically compared with the experimental measurements providing thereby many insights to lamp operation and guiding further modeling work. Amongst several important outcomes of the work is the observation of the effect of thermal diffusion on the relative concentration of Br atoms in the high temperature, intra-coil region.