Lateral Boundary Conditions for Heat Transfer and Electrical Current Flow during Vacuum Arc Remelting of a Zirconium Alloy

Abstract

Some aspects of the boundary conditions for heat transfer and electrical current along the walls of a vacuum arc remelting (VAR) crucible were investigated experimentally and numerically. Experimental measurements of the temperature and current in the crucible during the remelting of a Zircaloy2 electrode were performed in an industrial VAR furnace. In order to interpret the experimental data obtained, a detailed model of heat conduction in the crucible, including a partially new set of boundary conditions, was then developed. This model avoids some traditional simplifying assumptions. It accounts for both longitudinal and transverse heat transfers in the crucible and does not neglect transient effects. Regarding the boundary conditions, an important new feature of the model is to allow for the possibility of water boiling effects at the crucible-water interface The second improvement of the boundary conditions concerns the inner wall of the crucible, where a more refined description of the power input to the crucible has been developed to account for the energy transferred by the electric arc and the power associated to radiation losses of the electrode side surface. The proposed model provides a fair reproduction of the temperature distribution measured during the experimental melt. According to the numerical results, the peak of the temperature distribution along the crucible occurs slightly below the ingot top. An estimate of the fraction of the melting current transferred effectively to the ingot is derived from the experimental curves.