This paper deals with a two-temperature, two-dimensional modelling of a mercury high-pressure plasma stabilized by walls. We consider here a plasma composed of neutral particles, singly ionized positive ions and electrons. Both electron and heavy particle energies are supposed to follow Maxwell distribution functions at different temperatures. Moreover, the electrons were supposed to be carried by the heavy particles in their laminar convection movement. Hydrodynamic conservation equations are then solved by using a 2D semi-implicit finite element scheme. After validation the model is used to discuss deviations from thermal equilibrium due to external arc parameters such as arc current and pressure. These deviations are expressed as differences between electron and heavy particle temperatures. Our results confirm quantitatively for the first time the existence of thermal equilibrium deviations in such types of discharge. These deviations could be significant in many cases, especially when current or pressure is relatively low. Furthermore, we show that, in such types of discharge, the hot core is always closer to thermal equilibrium than the outer discharge jacket.
This paper deals with the modelling of the convection processes in high-pressure mercury arcs. Temperature and velocity fields have been calculated by using a 2D semi-implicit finite-element scheme for the solution of conservation equations relative to mass, momentum and energy. After validation, this model was applied to the study of the influence of arc external parameters such as mercury charge and tube diameter on the convective processes. It was found that stable laminar mono-cellular convection flow occurs at low values of tube diameter for a cylindrical burner and/or a low mercury charge. Finally, we considered in detail the region behind the electrodes, where an accumulation of mercury is observed. The evaluation of this amount of mercury `trapped' in these regions is of prime importance for a good description of the distribution of mercury in the burner and for a correct evaluation of the total discharge pressure.
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