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Experimental

Similarity Considerations

In the gas-stirred system, the fluid flow and mixing of the bathe are caused by momentum transfer between blown gas and liquid. The flow rate of injected gas in the model can be determined by the modified Froude number which was defined by

where H is the height of the ladle.

For N tuyeres with equal inner diameter d, the superficial velocity u was given by

where Q is the flowrate.

Substitute Eq. (2) into Eq. (1), we obtain

If we assume both of the full scale ladle and water model using the same number tuyeres the following equation can be used to determine the gas flowrate in the model.

where the subscripts 1 and 2 stand for model and full scale ladle, respectively.

Experimental Apparatus

Figure 1 showed a schematic of the experimental apparatus. Experimental work was carried out in a one-third scale water model of typical 40-tonne ladle. The main variables involved in the present consideration were listed in Table 1. Based on Miao Yong Zhu and Takeo Inomoto’s research [4], we focused the effect of single tuyere or double tuyeres on mixing time combined with the design of the domestic ladle bottom. Eight kinds of bottom blowing arrangements with universal representation were designed in this study. Figure 2 showed different configurations of

Experimental apparatus

Fig. 1 Experimental apparatus

Table 1 The main variable associated with present studies

Full scale ladle (40t)

Water model (M:3)

Bottom diameter (mm)

2065

596

Top surface diameter (mm)

2289

662

Height (mm)

2482

730

Diameter of tuyere (mm)

80

27

Density of liquid (kg/m3)

7000

1000

Eight types of tuyeres arrangement in the ladle

Fig. 2 Eight types of tuyeres arrangement in the ladle

the tuyeres used in experiment. The ladle was filled with tap water with the help of a pump and compressed gas was purged at a definite scaled down rate into the vessel through the bottom tuyeres. The gas flowrate was maintained constant for a particular experiment was with the help of rotameters. In the Fig. 2, tuyere 1 was at the radius of 1/3; tuyeres 2, 5 and 7 were at the half radii in the ladle (±R/2); tuyeres 3, 4, 6 and 8 were at the radius of 2/3.

In this research, nitrogen and hydrogen were used. The gas purging rate in the actual ladle in the plant ranges between 0.4 and 4 m3/h which corresponds to 12120 L/h of nitrogen and hydrogen flowrates for one-third scale water scale water model experiments. KCl solution of 1 N strength was used as the tracer and 50 ml of tracer solution was added for each experiments. An electrical conductivity probe was placed at 200 mm above the bottom and at 3R/4 from the center of the ladle. Another one was placed at 200 mm below the liquid level and also at 3/4R from the center of the ladle. The two probes were fixed on a straight line. The conductivity of the water was detected by the electrical conductivity meter which was connected to a personal computer through a pico log data acquisition system.

Before starting the experiments the probes were calibrated. The mixing time was defined as the time required from the instant of tracer addition until the conductivity meter displayed consistent. Mixing times were measured three times for a given set of experimental conditions, the mean value then being reported as the measured mixing time.

 
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