What is a Tundish?
In the continuous casting process, an intermediate vessel called the tundish is installed between the molten steel ladle and the mold. Traditionally, the tundish has the following roles: distributor of molten steel to molds, buffer to ensure uninterrupted molten steel feed during a ladle change, and vessel to facilitate the flotation and removal of inclusions.
A residence time distribution (RTD) analysis is one of the ways to quantify the mixing characteristics in a reactor. The characteristics of flow and reaction can be quantified and evaluated by obtaining an F-curve (Fractional Curve, F), C-curve (Concentration Curve, C), and by analyzing the patterns of those curves. Also, the RTD analysis can help to design an efficient flow reactor.
Residence Time Distribution (RTD)
The RTD is a probability distribution function that describes the amount of time that a fluid element could spend inside the reactor. Chemical engineers normally use the RTD in order to characterize the mixing and flow phenomena in a reactor or to compare the behaviors in a real reactor to their ideal model. This is useful not only for troubleshooting in a real reactor but also for estimating the yield of a reaction or for a new reactor design.
The theory of residence time distributions generally begins with three assumptions:
- The reactor is at the steady state.
- The transfer at the inlet and the outlet take place only by advection.
- The flow is incompressible.
An application of RTD analysis is in the steelmaking process. Let’s take an example of using RTD analysis for designing a tundish for metal casting.
The method of measuring the residence time in the tundish can be obtained by injecting a tracer into the inlet at a certain time (t = 0) and measuring the concentration of the tracer at the outlet over time.
The calculated minimum residence time, the average residence time, and the size of the stagnation zone can help design a highly efficient tundish. In this case, it can be considered that the long residence time can reduce the inclusions remaining in a melt, but the large stagnation zone can cause temperature drop of the melt.
The simulation results show that a CFD analysis can help analyze and make changes to the tundish design and enable more efficient flow reactors. If you’d like to give it a try for other metal casting simulations, SimScale is offering the possibility to use Computational Fluid Dynamics completely in the web browser. Start a 14-day free trial here.
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