and Shun-HuaXIANG Taken the~efining process in an 18t AOD vessel for example. the "back-attack" phenomena of the horizontal rotating and non-rotating gas jets and their effects on the erosion and wear of the refractory lining were investigated in a water model. For this refining process, the two-tuyere (

The flow and mixing characteristics of molten steel during the vacuum circulation refining, including RH(Ruhrstahl-Heraeus) and RH-KTB(RuhrstahI-Heraeus-Kawasaki top blowing) processes, were investigated on a 1/5 linear scale water model of a 90 t multifunction RH degasser. The circulation rate was directly and more accurately determined, using a new method by which the more reliable results can be obtained. The fluid flow pattern and flow field in the ladle were demonstrated, observed and analyzed. The mixing time of liquid in the ladle was measured using electrical conductivity method. The residence time distribution in the RH model was obtained by tracer response technique. The influence of the main technological and geometric factors, including the gas top blowing (KTB) operation, was examined. The results indicated that the circulation rate of molten steel in the RH degasser can be fairly precisely calculated by the formula : Qip : "-"~""'~a aq~ no. 26.~un0.69 ~dn~ 80 (t/min) , where Q~ -the lifting gas flow rate (NL/min) ; D, and Dd-the inner diameters of the up and down-snorkels (cm), respectively. The maximum value of circulation rate of molten steel in the case of the 30 cm diameters either of the up-and down-snorkels for the RH degasser (the "saturated" rate) is approximately 31 t/min. The corresponding gas flow rate is 900 NL/min. Blowing gas into the vacuum chamber through the top lance like KTB operation does not markedly influence the circulatory flow and mixing characteristics of the RH process under the conditions of the present work. There exist a major loop and a large number of small vortices and eddies in the ladle during the RH refining process. A liquidliquid two-phase flow is formed between the descending stream from the down-snorkel and the liquid around the stream. All of these flow situation and pattern will strongly influence and determine the mixing and mass transfer in the ladle during the refining. The correlation between the mixing time and the stirring energy density is rm oC ¢ -o.50 for the RH degasser. The mixing time rapidly shortens with an increase in the lifting gas flowrate. At a same gas flow rate. the mixing times with the up-and down-snorkel diameters either of 6 and 7 cm are essentially same. The 30 cm diameters either of the up-and down-snorkels for the RH degasser would be reasonable. The concentration-time curve showed that three circulation cycles are at least needed for complete mixing of the liquid steel in the RH degasser.

Based on fundamentals of the dynamics and thermodynamics of compressible fluid flow as well as heat transfer, the basic equations and formulae for characterizing and calculating the gas flow properties in tubular and annular type tuyères (constant cross‐sectional area lances) under the influence of a heat source are derived. The calculation procedures of the properties at different discharge states through a tuyère are given. For the case of an annular‐tube type tuyère used for an AOD (argon‐oxygen decarburization) vessel of 18 t capacity, the distributions of the inner wall temperatures of the tuyère and the gas stagnation temperatures along its length have been more reasonably determined. The friction coefficients of its main tuyère and subtuyère to the gas flows during injection refining have been fixed by comparison of the pressure‐flowrate (P‐Q) experimentally measured in relationship to the results of trial calculations.

The flow properties of the gases in an annular‐tube type tuyère used for an 18 t AOD vessel were analyzed using the equations and calculation formulas presented in Part I of this work. The influence of the heating and friction effects, the gas supply pressure, and the gas type and composition, on the properties were examined. The results showed that the properties in a tuyère are significantly changed due to the presence of a heat source. This has a similar effectiveness as increasing the friction action and obviously reduces the gas flowrate at the tuyère outlet. When designing a tuyère used in a practical process of metallurgy and calculating the flow properties of gas in the tuyère, the heating effect from the high temperature melt and refractory lining should be taken into account. The gas supply pressure has a decisive effect on the properties. The type and composition of the blowing gas will also influence the properties. For a given tuyère and blowing system, appropriate blowing pressures for different gases, particularly for subtuyère gases, should be used according to the technological requirements of the different refining periods.