Model study of turbulence structure in a bottom blown bath with top slag using conditional sampling

Water model experiments were carried out to study the effect of top slag on the turbulence structure in a molten steel bath agitated by bottom gas injection. Water and silicone oil were used as models of molten steel and slag, respectively. Air was injected through a single-hole bottom nozzle so that the reverse emulsification of the silicone oil occurred at the silicone oil-water interface. Silicone oil droplets thus generated were carried deeply into the lower water layer. Turbulence measurements were made using a two-channel laser Doppler velocimeter (LDV) in the presence and absence of the top oil layer. A conditional sampling method called the four-quadrant classification method was applied to detect large scale coherent motions in the vertical bubbling jet as well as in the recirculation region. The structure and intensity of turbulence inside the bubbling jet were strongly affected by bubbles. In the absence of the top oil layer, higher momentum fluid motions directed from the centerline of the bubbling jet to the sidewall of the vessel were mainly responsible for the turbulence production in the bubbling jet, while lower momentum fluid motions directed from the sidewall toward the centerline governed the turbulence production in the recirculation region. On the other hand, in the presence of the top oil layer, the coherent motion in the bubbling jet was also affected slightly by the top layer except for the center of the bubbling jet, whereas any distinguished coherent motion was not observed in the recirculation region, and hence, turbulence production was weak there.