A STUDY OF THE CONVECTIVE FLOW AS A FUNCTION OF EXTERNAL PARAMETERS IN HIGH-PRESSURE MERCURY LAMPS

This paper deals with the modelling of the convection processes in hig h-pressure mercury arcs. Temperature and velocity fields have been cal culated by using a 2D semi-implicit finite-element scheme for the solu tion of conservation equations relative to mass, momentum and energy. After validation, this model was applied to the study of the influence of are external parameters such as mercury charge and tube diameter o n the convective processes. It was found that stable laminar mono-cell ular convection flow occurs at low values of tube diameter for a cylin drical burner and/or a low mercury charge. Finally, we considered in d etail the region behind the electrodes, where an accumulation of mercu ry is observed. The evaluation of this amount of mercury 'trapped' in these regions is of prime importance fora good description of the dist ribution of mercury in the burner and for a correct evaluation of the total discharge pressure.