Fluid Flow, Thermal Stratification, and Inclusion Motion During Holding Period in Steel Ladles
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as many of the inclusions as possible from liquid steel is a principal steelmaking objective. Holding period is routinely required in the practice of steelmaking in order to improve the cleanliness of the liquid steel. Meanwhile, the superheat of the liquid steel in the tundish is one of the critical factors determining the quality of the steel product. Maintaining the temperature of the liquid steel supplied to a continuous caster via a tundish within a narrow band of the superheat target is necessary. The temperature of ladle stream has a significant effect on the bulk tundish temperature during casting. However, inevitable heat loss from the liquid steel to the ladle refractory not only results in continuous decrease of the melt temperature but also leads to natural convection and thermal stratification in the melt during the ladle holding period, which strongly influences the ladle stream temperature. Thus, it is necessary to understand the thermal state of the melt in the ladle during the holding period. The melt stratification was numerically simulated by Ilegbusi and Szekeley[1] and in their study, the stratification could be reduced through the use of magnetic stirring to promote bulk mixing. Austin et al.[2] conducted a transient analysis of the temperature and velocity distributions of steel during ladle standing and
HAOJIAN DUAN, YING REN, and LIFENG ZHANG are with the School of Metallurgical and Ecological Engineering, University of Science and Technology Beijing (USTB), Beijing 100083, China. Contact e-mails: [email protected]; [email protected] Manuscript submitted October 18, 2018.
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draining using a mathematical model based on the PHOENICS package. The effects of stand time, ladle cooling rate, draining rate, and ladle geometry on the ladle stream temperature had been investigated. A mathematical model on the transient fluid flow and heat transfer was built by Chakraborty and Sahai[3] to investigate the effect of slag cover on heat loss and liquid steel flow in ladles before and during teeming to a continuous casting tundish. Two different heat loss conditions had been assumed at the free surface of the melt to simulate the insulating effect of slags of varying thicknesses. Interestingly, a significant temperature stratification was observed in the melt for the case of insulated top free surface after 20 minutes of holding, while the temperature of the teem stream maintained at a near-uniform value over the casting period. Grip et al.[4] measured the thermal stratification in the ladle by thermocouples penetrating into the melt at different levels. After that, a three-dimensional computational fluid dynamics (CFD) model was developed to simulate the natural convection flow in ladles and verified the model with the measurements of temperature in 107and 7-ton ladles.[5] Using the PHOENICS package, Olika et al.[6] studied the ladle melt stratification phenomena by numerical simulations. The transient thermal boundary condition was obtained from a temperature simulation mode
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