A Water Model Study of Impinging Gas Jets on Liquid Surfaces
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CTION
THE
basic oxygen furnace (BOF) process uses supersonic oxygen jets that impinge on the metal bath surface, and the impingement process promotes the refining reactions and slag formation. The BOF has an extremely high refining rate partly because of the large amount of interfacial area created among the metal, slag, and gas phases by the high jet momentum; the metal and gas phases are considered to be emulsified in the slag layer.[1] The contribution of the extra area to the overall reaction rate is estimated to be less than 50 pct.[2] The other site for the high reaction rate is the hot spot at the jet impingement or impact point. The temperature measured by optical pyrometry around that impingement point is 2273 K to 2673 K (2000 °C to 2400 °C), which is 773 K to 1073 K (500 °C to 800 °C) higher than bulk bath temperature, and it is estimated that 75 to 80 pct of the carbon is removed in the jet impact zone.[2] Therefore, the effects of the oxygen jet are important for the determination of the following:
The liquid cavity shape and area at the impingement point.
Droplet formation and the subsequent droplet trajectory and residence time in the slag.[3]
HO YONG HWANG, formerly Graduate Student, Steel Research Centre, McMaster University, Hamilton, ON L8S 4L7, Canada, is now Research Engineer, ArcelorMittal Global R&D, East Chicago, IN 46312. GORDON A. IRONS, Dofasco Professor of Ferrous Metallurgy and Director, is with the Steel Research Centre, McMaster University. Contact e-mail: [email protected] Manuscript submitted December 19, 2010. Article published online December 1, 2011. 302—VOLUME 43B, APRIL 2012
The transfer of momentum to provide stirring in the metal bath. The current state of knowledge for each of these aspects will be reviewed briefly. A. Cavity Shape In principle, the cavity shape and area are a result of the combined effects of the dynamic pressure from the jet, gravity, and the capillary forces. Molloy[4] classified the response of the liquid surface to an impinging jet into dimpling, splashing, and penetrating stages; the classification criteria were based mainly the surface stability as a function of the gas impingement velocity. Banks and Chandrasekhara[5] were the first investigators to develop a fundamental relationship between the momentum of a turbulent jet and the depth of penetration no. They combined a turbulent jet centerline velocity relationship[6] with a balance between gas dynamic pressure and buoyancy at the impact point to obtain the following dimensionless relationship: _ M p n0 n0 2 1 þ ¼ ½1 ql gh3 2K2 h h An equivalent relationship was developed by Turkdogan.[7] Koria and Lange[8] extended the analysis to jetting from multiple holes. Qian et al.[9] modified Eq. [1] slightly and _ l gn0 d2 with quadratic polynomials of fitted Fq ¼ M=q 0 h þ n0 =d0 to experimental data. Recently, Nordquist et al.[10] reviewed the cavity depression depth data and concluded that Eq. [1] is not accurate for nozzle diameters less than 2 mm. They derived a new relationship based on a macros
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