Transient flow and heat transfer in a steelmaking ladle during the holding period
- PDF / 400,511 Bytes
- 9 Pages / 612 x 792 pts (letter) Page_size
- 85 Downloads / 188 Views
I. INTRODUCTION
IN metallurgical industry, the temperature of liquid steel supplied to a continuous caster via a tundish has to be controlled to a tight limit in order to obtain good quality steel. The temperature of steel emerging from the ladle has significant effect on the bulk tundish temperature during casting. Natural circulation within the molten steel appears due to heat loss from steel into the refractory, and thermal stratification in the melt will be formed during the ladle holding period. The mean steel temperature in the ladle can be predicted with reasonable accuracy by taking the sources and mechanisms of heat loss into consideration.[1,2] However, the temperature stratification in the ladle may strongly influence the ladle stream temperature. It is desirable that the change of the ladle stream temperature with time should not be great in order to obtain a small variation of the tundish temperature during the ladle casting. A good understanding of the flow and heat transfer occurring in this process is therefore essential for industrial operations. A few studies on this issue have been conducted. Hlinka and Miller[3] showed that the ladle pouring temperature varies due to heat losses from molten steel into the surrounding refractory layers. The process is transient and leads to turbulent natural convection flow in the molten steel. This phenomenon was numerically simulated by Ilegbusi and Szekeley,[4] who focused on reducing the effect of stratification by using magnetic stirring to promote bulk mixing. They showed that gentle stirring could be enough to minimize stratification. Austin et al.[5] carried out a transient analysis of the temperature and velocity distributions of steel during ladle standing and draining, using the PHOENICS code. Effects of ladle cooling rate, stand time, draining rate, and ladle geometry on the ladle stream temperature were calculated. Based on their numerical prediction, they suggested a simple empirical correlation to represent the dependence of the rate of increase in temperature difference between the central top and central J.L. XIA, Senior Researcher, and T. AHOKAINEN, Research Manager, are with the Laboratory of Materials Processing and Powder Metallurgy, Helsinki University of Technology, FIN-02015 HUT, Espoo, Finland. Manuscript submitted August 16, 2000. METALLURGICAL AND MATERIALS TRANSACTIONS B
bottom of steel, , and the average cooling rate of the steel into the refractory, c:
⫽ 2.0c This relation can be used to estimate the extent of thermal stratification (defined as the temperature difference between the central top and bottom of liquid steel), but, because the average cooling rate is still unknown, the previous relation is not practical to use. It was shown that the stratification increases with time, and the outflow rate has a great effect on both the flow pattern and the temperature profile of the outlet stream. Rapid tundish filling can reduce the influence of ladle stratification. It should be noted that a uniform and constant heat flux over th
Data Loading...
