Thermal analysis of twin-channel induction furnaces
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8/28/03
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Thermal Analysis of Twin-Channel Induction Furnaces J.I. GHOJEL Twin-channel induction furnaces (TCIFs) are used extensively in many processing industries due, mainly, to their relatively low operating costs. However, thermal stresses in the refractory lining caused by high temperatures during the loading cycle can cause erosion of the lining and premature inductor failure. Prevention of premature failure by close monitoring of the thermal regime of the inductor is very important to operators and relatively simple and reliable tools need to be developed to this end. The present work is an attempt to develop such a tool using thermal modeling software and unidirectional axial channel flow estimation from analysis based on the first law of thermodynamics. This avoids the complications and uncertainties associated with the coupled multiple field analysis approach. The results of the analysis show plausible agreement with the reported flow data and a comprehensive set of scenarios can be devised on the basis of the developed approach to simulate start-up, transient operation, and steady-state operation of TCIFs.
I. INTRODUCTION
TWIN-CHANNEL induction furnaces (TCIFs) are used extensively for melting and holding metals and alloys in many processing industries. This is due to their high overall efficiency, good degassing, and homogenization of the melt, low oxide, and slag formation and low energy cost (as a result of the potential to use preferential electricity rates). Figure 1 is the vertical cross section of a TCIF (adopted from Reference 1 and modified) showing the inductor (highlighted by the dashed box) with the two side channels and central channel, main pot, electric field, and molten metal flow. The flow shown by the arrows is the typical pattern observed in the jetflow type TCIF. Multi-inductor furnaces with two or more inductors are usually designed with the inductors mounted on the sides of the pot, as shown in Figure 2. Alternating current in the primary coil wound around two sides of a continuous iron core induces large current densities in the molten metal in the channels, which form single-turn secondary coils (Figure 1). The currents induced in the channels heat the metal in the inductor, which mixes via the side channels with the metal held in the melting or holding pot. The relatively colder metal flows back to the inductor through the central channel. Large pots are normally designed with several channel induction heaters in order to meet their high melt rates. It is generally accepted that the function of the primary coil is to induce large electric current densities in the channels and heat the metal (Joule heating). The electromagnetic field in the system acts primarily in the planes perpendicular to the axes of the channels and no axial flows, resulting from electromagnetic forces, along the channels axes are detected. [1,2] The flow in the crosssectional areas of the channels exhibit a double-vortex flow pattern resulting from the interaction of the stray pri-
J.I.
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