Investigation of Spray Cooling Heat Transfer for Continuous Slab Casting

The spray cooling technology is a key technology in the continuous casting process, which has a significant influence on the product quality. In order to ensure high quality standards at different operating conditions, modern continuous casting machines provide the possibility to vary the cooling with respect to intensity, width, stand off distances, etc. For design purposes, numerical simulation is used to calculate the feasible operating range of the caster. During casting operation, an online thermal tracking model, e.g., Dynacs, computes the set points of the cooling intensity depending on the actual casting conditions. Both tools use mathematical models which require precise information about the cooling characteristics of spray nozzles. The subject of the present work is the modeling of the convective heat transfer due to spray cooling using flat spray air-mist nozzles, which are widely used in slab casting machines. Measurements of the spray pattern and air/water flows were carried out on a spray test stand in order to investigate the profiles of the water flux at different air/water pressures and different distances from the nozzle tip to the surface. The air-to-water ratio was chosen according to the well-proven Siemens VAI air pressure control curve. The heat transfer coefficients due to spray cooling were measured using an experimental stand which allows spray cooling experiments up to a surface temperature of 1250 degrees C. Based on the obtained experimental data a heat transfer correlation for air-mist sprays is developed to describe the effect of the different operating conditions on the spray cooling heat transfer coefficient. The correlation shows good agreement between the heat transfer coefficient profiles from prediction and experiment.