In this work, heat trials (14 heats made on two sequences) were conducted to identify the minimum Ca addition possible for preventing submerged entry nozzle clogging and for improving the steel Cleanness. These trials were conducted on two sequences, the first one aimed at reaching the minimum Ca addition practically possible and the second aimed at stabilising this addition level. Evaluation of the results was carried out using metallographic microscope observation and SEM/EDX analysis. It was found that submerged entry nozzle clogging was successfully prevented by decreasing the amount of Ca addition from 0?095 to 0?06 kg Ca/ton steel. Moreover, it was possible to identify the effect of such addition level on converting alumina inclusions to globular Ca-aluminate and reducing the CaS inclusion formation range from 4-41 to 0?05-7?61%.

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3D computational fluid dynamics models using Fluent were developed to investigate the steel melt flow during waiting and arcing time. Both models were transient that analyzed 60 seconds to investigate the flow characteristics considering variation in steel melt thermo-physical parameters and operating conditions. The velocity of melt movement was high enough to make a turbulent flow (solved with realize k-ε turbulence model). It was found that the steel melt flow velocity increases by a combined effect of the steel melt temperature and composition, and slag pressure. The slag pressure increases by a double effect of slag density and height, and the steel melt fluid flow velocity changes with the slag pressure. The effect of the slag thickness is more significant than the effect of thermo-physical properties of steel melt. Although, the maximum steel melt velocity "during arcing time" may be as large as 0.67 m/s located at steel met outlet, the melt exhibits completely dead zones with minimum flow velocity distribution especially at the bottom and circumference areas. This indicates the importance of combined stirring and large reaction rates to achieve a complete homogeneous melt especially at bottom and circumference areas.

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