A new decarburization model for the RH system was constructed to calculate the decarburization reaction using a three-dimensional fluid dynamics program. The behavior of Ar gas and the entire fluid flow in the RH process were considered. On the basis of this fluid flow, the decarburization reaction could be calculated by establishing the decarburization reaction model, which considers thermodynamics, reaction kinetics, and the decarburization sites (Ar bubble surface, bath surface, and the CO bubble formation at inner sites). The model showed good agreement with two RH operation results. Using this numerical model, the contributions of each reaction were investigated.KEY WORDS: decarburization; reaction model; reaction site; reaction area; reaction rate.where g is the acceleration due to gravity (m/s 2 ), r l and r g are the densities of the Ar gas and the melt (kg/m 3 ), V p is the volume of the plume (m 3 ) and a is the average volume fraction of the gas. The plume volume was calculated from the plume shape, which is affected by the pressure of the vacuum vessel, nozzle number and position, gas flow rate etc.. The average volume fraction is the total volume ratio of gas in the plume realm. In addition, gas bubble expansion due to the pressure drop and heat transfer from melt during rising was calculated and this effect was considered when calculating the total buoyancy force. In the Ref. 9), the bubble expansion due to only pressure drop was considered. In this study, the numerical model was modified to consider both the thermal expansion and pressure drop, Szekely's model 11) is modified as In Eq. (2), r l is the density of the melt, R b is the radius of the bubble, T is temperature in the bubble, R b and T 0 are radius and temperature at the nozzle respectively, P V is the pressure of the vacuum vessel and H is the height of the melt. To solve Eq. (2), the temperature should be known. ) and C is the heat capacity (J/kg · K). h is the heat transfer coefficient (J/m 2 · s · K) and the value can be derived from the penetration theory with the assumption of gas phase control. Komarove et al. derived heat transfer coefficient from experiments.12) Because the analysis in the Ref. 12) was based on spherical and constant size bubble, there should be some difference in the value of h and further study should be necessary to derive more realistic h value.The buoyancy force calculated by Eq. (1) was inserted as the external force for the velocity components (u, v, w) in the three dimensional Navier-Stokes equation to calculate fluid flow. The numerical model can predict the effects of the operational conditions and shapes of the RH system on fluid flow.
13)
Calculation of Decarburization ReactionIn this study, the decarburization reaction was simulated by calculating the dissolved carbon concentration during the RH process. The numerical model included mass transport of dissolved carbon and oxygen due to convection and diffusion and the reaction rate at the reaction sites. The reaction rate was calculated respectively...
