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Optimization of the heat flux distribution in cold hearth electron beam refining process
A Cold Hearth Electron Beam (EB) Refining process is used for refining of high-performance alloys used in aerospace
applications. A cold hearth is a water-cooled copper crucible through which the molten metal is made to flow for removal of any impurities and for dissolution of inclusions. An electron beam is used as a
heat source to both melt the incoming material and to keep it molten as it flows through the hearth. The low temperature of the crucible wall gives rise to a protective skull of solidified material to
form on the crucible wall. The size of the pool formed and the flow induced in the pool is controlled by various design and operating parameters such as the design of the crucible, the mass flow rate of
the alloy, and the amount of heat flux provided by the EB gun.
In this study, we have developed a model for prediction of the transport phenomena in the EB cold hearth and validated the model
using the data from a production hearth. The model involves efficient analysis of fluid flow, heat transfer, and phase change using a fixed-grid method. The flow is strongly influenced by the buoyancy
and Marangoni forces and typically, the pool is shallow. The shape of the pool is not known a priori. It is determined from the temperature field, which is a result of the energy supplied to the hearth
and the radiative heat losses to the cooling water and the surrounding gas. A Lagrangian method is used for the prediction of the motion and dissolution of inclusions. The size and shape of the pool is
strongly controlled by the amount and the distribution of the heat flux on the pool surface. The shape of the pool, in turn, governs the flow field, and the fate of the inclusions.
This model was
applied for the optimization of the heat flux distribution in a production hearth. Model-based parametric analysis allowed determination of the EB gun pattern that maximized the probability of the
removal of inclusions.
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