Effects of Salt Tracer Volume and Concentration on Residence Time Distribution Curves for Characterization of Liquid Steel Behavior in Metallurgical Tundish

Abstract

The residence time distribution (RTD) curve is widely applied to describe the fluid flow in a tundish, different tracer mass concentrations and different tracer volumes give different residence time distribution curves for the same flow field. Thus, it is necessary to have a deep insight into the effects of the mass concentration and the volume of tracer solution on the residence time distribution curve. In order to describe the interaction between the tracer and the fluid, solute buoyancy is considered in the Navier–Stokes equation. Numerical results show that, with the increase of the mass concen-tration and the volume of the tracer, the shape of the residence time distribution curve changes from single flat peak to single sharp peak and then to double peaks. This change comes from the stratified flow of the tracer. Furthermore, the velocity difference number is introduced to demonstrate the importance of the density difference between the tracer and the fluid.

Challenge of Residence Time Distribution Curve in Tundish for Continuous Casting of Steel

“…In order to investigate the effect of the tracer on the fluid flow in the tundish, Ding et al [ 19,20 ] developed two dimensionless numbers, δ (velocity difference number) and Tr (tracer dimensionless number), to reveal the effect of the solute buoyancy on the flow behavior. As the tracer moves toward the outlet, the greater the tracer concentration is, the stronger the effect of the tracer on flow behavior is. where u , v , and w are the velocity at x , y , and z direction in the case of actual tracer (); , , and are the velocity at x , y , and z direction in the case of ideal tracer (). where β is the solute expansion coefficient of the tracer (−); g is the gravitational acceleration (); l is the height of liquid level (m); C is the tracer mass concentration (−); and U is the velocity of fluid ().…”

“…But in the current case, the double peaks of the RTD curves come from the stratified flow in Figure 6 , which is caused by the density difference between the water and the tracer. [ 19 ] Therefore, the short‐circuit flow may be not the only reason for the double peaks of the RTD curve in the water model.…”

“…Reproduced under the terms of the CC‐BY license. [ 19 ] Copyright 2021, The Authors. Published by Multidisciplinary Digital Publishing Institute.…”

“…This is the short‐circuit flow; 2) There are density difference between the tracer and the water. The strong solute buoyancy can lead to stratified flow, so the RTD curve will have two peaks [ 19 ] ; and 3) If there is a multihole baffle in the tundish, multipeak also appears on the RTD curve. Theoretically, the number of holes in the baffle is the number of peaks on the RTD curves.…”

“…The ideal RTD curve obtained by mathematical model is usually different from the actual RTD curve obtained by water model. In order to highlight the effect of the tracer on the RTD curve, Chen et al [ 17,18 ] introduced the mixed composition fluid model into the traditional mathematical model to predict the tracer flow and Ding et al [ 19,20 ] considered the solute buoyancy into the momentum equations based on the Boussinesq approximation.…”