NUMERICAL INVESTIGATION OF AIR-MIST SPRAY COOLING AND SOLIDIFICATION IN SECONDARY ZONE DURING CONTINUOUS CASTING
thesisposted on 20.12.2021, 18:35 authored by Vitalis Ebuka AnisiubaVitalis Ebuka Anisiuba
As a result of the intense air-water interaction in the spray nozzle, air-mist spray is one of the most promising technologies for attaining high heat transfer. CFD simulations and multivariable linear regression were used in the first part of this study to analyze the air-mist spray produced by a flat-fan atomizer and to predict the heat transfer coefficient using the casting operating conditions such as air pressure, water flow rate, cast speed and standoff distance. For the air-mist spray cooling simulation, a four-step simulation method was utilized to capture the turbulent flow and mixing of the two fluids in the nozzle, as well as the generation, transport, and heat transfer of droplets. Analysis of the casting parameters showed that an increase in air pressure results in efficient atomization, increases the kinetic energy of the droplets and produces smaller droplet size thus, the cooling of the slab increases significantly. Also, a decrease in water flow rate, standoff distance and casting speed would result in more efficient cooling of the steel slab. The second part of the study investigated the solidification of steel in the secondary cooling region. Caster geometry and casting parameters were studied to evaluate their impact on the solidification of steel. The parameters studied include roll gap, roll diameter, casting speed and superheat. It was found that a smaller ratio of roll gap to roll diameter is more efficient for adequate solidification of steel without any defect. Casting speed was found to have a significant effect on the solidification of steel while superheat was found to be insignificant in the secondary zone solidification. The result from the air-mist spray cooling was integrated into the solidification model to investigate the solidification of steel in the entire caster and predict the surface temperature, shell growth and metallurgical length. To replicate real casting process, temperature dependent material properties of the steel were evaluated using a thermodynamic software, JMatPro. The air-mist spray model was majorly investigated using ANSYS Fluent 2020R1 CFD tool while the solidification of steel was studied using STARCCM+ CFD software. Using the findings from this study, continuous casting processes and optimization can be improved.