Discussion About Model of Residual Time Distribution for Tundish

摘要

Tundish metallurgy is critical in continuous casting process, and it has much to do with the clean steel technology. And the most effective and convenient way to evaluate the tundish designing or tundish metallurgy is to calculate different regions' volume fraction in the tundish, such as plug flow region, backmix flow region, bypass flow region and dead region. Till now this can only be solved through some calculation models based on the analysis of residual time distribution (RTD) curve, and RTD is referred from chemical reaction engineering. But RTD is far away from metallurgy field because complicated mathematical calculation and analysis are covered. Few metallurgists do further research about its applicability and correctness since modified mixed model and combined model are proposed and widely used in tundish metallurgy. In this paper, the short-coming of these two calculation models are pointed out and explained. Then it finds to irrationally define the dead region's volume fraction equals to 1-θav, the reason is that this equation doesn't definitely describe the definition of dead region, which is defined the region where tracers spend more than twice mean residual time, so this equation does not characterize the property of dead region. In some case, minus value of the dead region's volume fraction are obtained if this equation is adopted;and it is also not reasonable to define plug flow's volume fraction equals to 1/2(θmin + θmax) or θmin, because θmin is also influenced by backmix flow. Even when θmin and θmax have the same value, the plug flow volume fraction is different according to variance σ2. Then in this paper, these two models are further proved based on mathematical simulation, it suggests to calculate the different regions' volume fraction in tundish inadequately through the present models available, and to trustless use the results to guide the tundish designing and tundish metallurgy process. At last it suggests that another new calculation model should be attempted to calculate the different regions' volume fraction in the tundish.