A heat transfer study for a partially immersed refractory rod in a plasma

The thermal behavior of a tungsten rod partially immersed in a plasma flame is analyzed. The longitudinal temperature profiles are obtained by numerical solution of the heat balance equation. Results show that a heat transfer model consisting of pure natural convection up to the plasma outer edge and forced convection inside the plasma, fails to predict temperatures at the hot tip of the rod. In order to make the experimental and calculated profiles to converge, one has to consider modifications in the mechanical and thermal conditions of the surrounding medium due to the presence of the rod in the plasma. This leads to the use, in the “cold” gas zone, of particular values of heat transfer coefficient h and of a parameter T_x which is defined only at the immediate boundary of the rod. The latter are given in the form of variations along the axis of the rod. This perturbation effect decreases with the rod diameter. Allowance is made for the variation of the thermal properties of the solid.