An Experimental and Mathematical Work on Single Bubble Behavior under Reduced Pressure

• During secondary steelmaking, argon bubbles are often passed through molten steel to ensure a clean and homogeneous product. The behavior of the bubbles and the capacity of the bubbles to stir the melt and remove impurities depends on their size, shape, and velocity. These factors depend on the ambient pressure of the melt, the temperature and flow rate of the gas and the geometry of the gas nozzles. There have been many studies that investigate the behavior of bubbles when the melt is under atmospheric pressure, but few when the melt is held under vacuum. This makes it difficult to optimize the argon blowing process. The current study addresses this lack of knowledge by studying bubble behavior when the melt is under vacuum. Physical modeling was used to analyze the effects of the reduced pressure and nozzle diameter on the bubbles’ initial diameter and ascent behavior in a molten steel. Moreover, a multiphase fluid dynamics solver for compressible fluids called ‘compressibleInterFoam’ was validated and used. Increasing the flow rate leads to larger initial bubble diameters and more frequent bubble formation, and increasing the nozzle diameter leads to larger initial bubble diameters and less frequent bubble formation. Decreasing the subjected pressure causes the bubble diameter to increase substantially but bubbles to form less frequently. For flow rates in the range of 5.0(mL·min-1)STP to 2000(mL·min-1)STP, the bubble diameter ranges from 6.0mm to 20.0mm. The frequency of bubble generation initially increases with flow rate before reaching a constant value. During the ascent, a bubble will shed several small bubbles at the bottom to reach a constant shape. In the steel-argon system, under laminar flow conditions, the maximum bubble width under a pressure of 0.2bar is 65mm and is 58mm under a pressure of 2.0bar. As the surrounding pressure increases, the maximum size of the bubble under the steady condition will decrease. These findings can be used to determine the bubble behaviors and to optimize the conditions of argon blowing to produce steel that is sufficiently clean, while minimizing argon usage.

Ämnesord

TEKNIK OCH TEKNOLOGIER  -- Materialteknik -- Metallurgi och metalliska material (hsv//swe)

ENGINEERING AND TECHNOLOGY  -- Materials Engineering -- Metallurgy and Metallic Materials (hsv//eng)

Nyckelord

ladle

single bubble

reduced pressure condition

physical modeling

mathematical modeling

Metallurgical process science

Metallurgisk processvetenskap

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