Mathematical modeling of a direct current electric arc: Part I. Analysis of the characteristics of a direct current arc
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3/4/04
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Mathematical Modeling of a Direct Current Electric Arc: Part I. Analysis of the Characteristics of a Direct Current Arc MARCO RAMÍREZ and GERARDO TRAPAGA A mathematical model is used to describe fluid-flow, heat-transfer, and electromagnetic phenomena in the arc region of a direct current electric arc furnace (DC EAF). Based on those model results, a detailed physical analysis of the arc was performed, where the numerical computations help to explain the arc structure, its behavior, and the highly coupled relationship among their main physical variables. This analysis leads to the conclusion that the arc behaves in such a way that all the arc characteristics are controlled by the expansion of the arc, which is the main feature used to physically describe the arc behavior. The arc expansion is evident from the arc shape, which is defined as the region where conduction of electricity takes place. The arc shape is clearly seen in several contour fields presented in this work, such as the current density, the magnetic flux density, the electric conductivity, the electric potential, and the temperature fields. The results of this article focus on process analysis, to provide insight into the inter-relationship among the arc variables, and to establish physical grounds to subsequently explore dimensionless analytical representations to describe the arc behavior.
I. INTRODUCTION
NOWADAYS the electric arc furnace (EAF) process represents almost 40 pct of the total crude steel production in the world.[1] From the two available technologies of this process (alternating current (AC) and direct current (DC) systems), the DC technology currently covers approximately 70 pct of the new EAF being commissioned around the world due to several advantages this technology has in comparison to the AC furnace.[2] The main purpose of the EAF process is to produce molten steel from scrap, direct reduced iron (DRI), pig iron, and other raw materials, to minimize the consumption of energy (in particular electric energy), and to increase productivity. Also, refractory and electrode consumption are still important issues for the steelmaking industry. All improvements associated with the EAF process have been related to reductions in operational costs or increases in productivity.[3] Many of these technological improvements have been successfully implemented, but all of them have something in common: an apparent empiric approach. The most recent trends in the industry show that the efficiency of the process is reaching a plateau where no further impact in the operation is being achieved. Therefore, it is our primary premise that a fundamental and rigorous understanding of the process will be the only ways to further improve the EAF operation. One of the most important areas of research in the EAF regards energy consumption, in which the arc region represents an important area. Modeling of the electric arc has been an academic challenge to many authors in the past due to the complex phenomena occurring inside this r
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