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A coupled numerical model based on computational fluid dynamics (CFD), termed a CFD-based nucleation-growth-removal model, has been proposed to investigate the nucleation, growth and removal of inclusions in a bottom-blown gas-stirred ladle during molten steel deoxidation.In order to account for the turbulent circulating flow induced by gas bubbling through the bottom, the k-e turbulence model was employed to evaluate time-averaged Reynolds stress while the fluctuation of the free surface of the melt was traced by means of the VOF technique. This model enables to couple transient flow fields, and temperature fields with concentration fields of elements and inclusions in melt so that it can meet the requirements of evolution of time-and space-dependent particle size distributions (PSD) without any given initial PSD of inclusions but directly from chemical reaction.The model was applied to the simulation of the molten steel deoxidation process in Fe-Al-O system in an argon gas-stirred ladle. The model successfully predicted important phenomena including turbulent recirculation flow patterns, streamline structure of steel melt, turbulence energy variation and its dissipation rate, transient temperature fields and particle size distributions of alumina inclusion. Comparison with some industrial data showed that the predicted PSDs were reasonable in time-dependent variation of inclusion size distribution.KEY WORDS: numerical modeling; inclusion; particle size distribution (PSD); nucleation; growth; removal; CFD; gas bubbling. 891© Miki et al.,25) and Sinha et al. 26) (tundish metallurgical processes), and more recent work by Sheng et al. 27) and Söder et al. 28) (ladle refining). To activate the models, one need to input an initial size distribution of inclusions, which comes from either experimental measurements or assumptions, to provide a starting point for numerical calculations. Therefore, the results predicted by a model for inclusion growth and removal are dependent to some extent on the validity of the initial particle size distribution (PSD) selected.• Theoretical models for the nucleation and growth of inclusions: Christian 29) gave a comprehensive review and summarization of the classical nucleation theories. Turpin and Elliott, 30) Turkdogan, 31,32) and Mukai et al. 33) applied the classical nucleation theories to steelmaking processes and analyzed inclusion formation and growth during molten steel deoxidation under a hypothesis of homogeneous nucleation. These theoretical models laid the foundation for the subsequent investigations.• Static numerical models for nucleation, growth and removal of inclusion: Attempts to develop general nucleation-growth models for molten steel deoxidation were marked by the work of Zhang and Pluschkell, 34) Doo et al.,35) and others. Although the model from the latter should virtually be a growth model rather than a real nucleation-growth model, Zhang and Pluschkell 34) borrowed ideas from Kampmann and Kahlweit,36) and put forward a static numerical model, w...

A water model study was undertaken to investigate bubble dispersion and inclusions removal by bubble adhesion in continuous casting mold. The water flow rate was varied in the range of 37-74 L/min, which is equivalent to 1.0-2.0 m/min of the casting speed in continuous casting process. The gas flow rate was varied in the range of 0-2.5 L/min. Silver coated hollow glass beads (SCHG) and plastic particles were used to imitate the inclusions and to investigate the effect of wettability, i.e., contact angle of the inclusions with liquid, on inclusion removal by bubble adhesion. Effect of gas and water flow rates on bubble dispersion in the mold was systematically determined. Inclusion removal at different gas and water flow rates was quantitatively determined. It was identified that the wettability of inclusions with liquid was a decisive factor in inclusion removal: with low wettability, i.e., high contact angle, removal efficiency increased with increasing gas and liquid flow rates, whereas removal efficiency was hardly affected by gas flow rate with high wettability, i.e., low contact angle.To interpret the results of the water model experiments, various computational fluid dynamics (CFD) models which had been reported were applied. None of them was able to represent the experimental results within an acceptable discrepancy. Two new CFD models, which employed a modified Reynolds number and force field theory around the bubble, were developed to simulate bubble dispersion and inclusion removal, respectively.The results indicated that these models could simulate bubbles dispersion and inclusion removal and showed reasonable agreement with results of water model in continuous casting mold.KEY WORDS: bubble; inclusion removal; water model; CFD; turbulence; continuous casting mold. desired level. (b) After fluid and bubble flow reached a steady state, the bubble flow pattern was investigated and recorded by a high speed camera with 1 000 frames per second through the observation window (10). (c) Through image analysis method, effects of the water and gas flow rates on the bubble size and bubble flow pattern were investigated. Three different gas flow rates were employed in the present study; that is, 0, 1.7 and 2.5 L/min, and also three different water circulation rates were used, i.e., 37, 56 and 74 L/min to simulate the steel casting speed of 1.0, 1.5 and 2.0 m/min, respectively. Inclusion RemovalThe apparatus and operation condition are the same as that for the bubble dispersion experiment. The apparatus was operated according to the following sequence: (a) First, the water tank (1) is filled with water, and the water valve (4) and the gas valve (5) are adjusted to a desired level. (b) To realize an overflow condition to help floated particles be removed from the top free surface, a small amount of water (225 mL/min) is kept flowing through the water valve (7). (c) Then a predetermined amount (4 g) of silver coated hollow glass beads (SCHG) or plastic particles were mixed with 50 mL water in a syringe and stirred u...