Mixing and Residence Time Distribution in an Inert Gas-Shrouded Tundish
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tundish was initially conceptualized as a mere vessel to continuously supply liquid steel to the continuous casting mold, researchers have started to realize its full potential. It is now a well-proven fact that the steel cleanliness can be enhanced by controlling melt flow patterns. Controlling melt flows in the tundish is a topic of interest to most steel makers. Melt flow characterization has been performed through computational fluid dynamics (CFD) simulations, particle image velocimetry (PIV), as well as residence time distribution (RTD) experiments. Residence time is defined as the time a single fluid element spends in the reactor vessel.[1] RTD is a quick and relatively inexpensive technique to characterize melt flow patterns that can provide us with valuable insights. Significant amount of research has been done on RTD in various types of tundishes using a variety of on-line measurement techniques such as
SAIKAT CHATTERJEE and KINNOR CHATTOPADHYAY are with the Process Metallurgy and Modelling Group, Department of Materials Science and Engineering, University of Toronto, 184 College Street, Toronto, ON, M5S 3E4 Canada. Contact e-mail: [email protected] AMJAD ASAD, CHRISTOPH KRATZSCH, and RU¨DIGER SCHWARZE are with the Institut fu¨r Mechanik und Fluiddynamik, Technische Universita¨t Bergakademie Freiberg, Lampadiusstrasse 4, 09599 Freberg, Germany. Manuscript submitted August 8, 2016. Article published online December 1, 2016. METALLURGICAL AND MATERIALS TRANSACTIONS B
colorimetry, conductimetry, and spectrophotometry.[1–4] Interestingly, the amount of work done on analyzing the effect of gas injection on fluid flow characteristics is rather scarce. Sahai and Ahuja[1] and Chang et al.[5] studied the effects of submerged gas injection and gas bubbling curtains on fluid flow and homogenization, whereas Srivastava and Koria[6] analyzed the effect of air flow through the shroud on fluid flow patterns. During inert gas-shrouding, there is some inherent entrainment of argon gas into the melt and it forms a bubble plume inside the tundish.[7–9] The authors believe that this type of bubble plume inside the tundish has a significant effect on the RTD and mixing behavior of the tundish. To prove this point, a simple water model experiment was devised where a 1 (N) NaCl solution was injected, and the total mixing time and change in water conductivity were recorded. The conductivity values were converted into dimensionless concentration and subsequently, the dimensionless concentration versus dimensionless time curves, known as C-curves were derived. A schematic diagram showing the experimental setup for measurement of tracer dispersion is shown in Figure 1. It consisted of a one-third scale tundish, water supply, compressed air supply, syringe for tracer injection, and data acquisition devices. Compressed air was used to simulate argon injections at 0 to 10 pct of steel entry flows. Data from the conductivity meters for all the cases were processed to obtain normalized C-curves. The dimensionless concentration C(h) was plott
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