Effect of Top Slag

Swirl motion of a bubbling jet occurs even in the presence of a thin slag layer on a molten metal layer. The bath surface oscillations, however, are strongly modulated compared with those in the absence of the slag layer. This section presents the effects of the top slag layer on the first kind of swirl motion of a bubbling jet and the behavior of the slag layer. 

The motions of the slag layer were classified into three categories, as shown in Figs. 5.47a-c. When the gas flow rate gg was lower than a certain critical value, the first kind of swirl motion was not observed (Fig. 5.47a). When gg exceeded the critical value, the slag layer disintegrated into small droplets (reverse emulsification). On average, the droplets did not rotate around the vessel axis, i.e., they remained at their initial position, but the bubbling jet rotated in the plume eye (Fig. 5.47b). 

As Qg increased further, the disintegrated slag layer clustered and rotated in the direction opposite to the direction of the bubbling jet (Fig. 5.47c). This result may be explained as follows. 

As gas is injected vertically upward into a still water bath, the initial angular momentum of liquid in the bath is zero. If a bubbling jet rotates, for example, counter clockwise, the water and silicone oil outside the bubbling jet rotate clockwise in order to satisfy the conservation law of angular momentum [35,37]. 

The three types of motions of the silicone oil layer can be mapped as a function of gas flow rate as shown in Fig. 5.48. It should be stressed that reverse emulsification, i.e., the formation of silicone oil droplets in the lower water layer occurs in the motions of Types 2 and 3. 

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