Thermal and transport modeling of high pressure discharge lamps

Summary form only given, as follows. A thermal model of plasma and bulb/electrodes of HID burners has been developed. It is based on the finite element CFD package FIDAP. The simulations presented are three-dimensional for horizontal burning position. The plasma model computes self-consistently the flow and pressure fields, the electrical field including operating voltage and the temperature field. The ohmic heat sources are computed from the electric field, the are shape is a result of the simulation. Optically thin radiation is treated as local energy sink. Optically thick radiation is simulated as a contribution to the effective thermal conductivity. The plasma is assumed to be in local thermodynamic equilibrium. The software has been successfully applied to Philips UHP-lamps, short are burners with pure mercury discharges at very high operating pressures. In these lamps natural convection is the dominating heat transfer mechanism. The temperature field shows a strong asymmetry between top and bottom. Consequently the heat flux onto the inner wall is strongly peaked to the top. The bulb/electrode models use this heat flux as boundary condition to compute the temperatures of all solid parts including the temperature at the top and bottom inner wall. The heat flux to the electrode tip is assumed to be proportional the operating current as computed by the plasma model. Outer wall temperatures and operating voltage are compared with experiments to calibrate the model.