Characteristics of eccentric bubble plumes in liquids
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I.
INTRODUCTION
IN a recent article,[u we investigated the hydrodynamics of air/water plumes in a large scale model of a metallurgical ladle. The vessel was cylindrical and the air was injected at the center. In the steel ladles, however, the stirring gas is usually introduced eccentrically. Whereas there are many studies of the center-injected bubble plumes (literature cited, in Reference 1), only a few investigations have been carried out on the eccentric-injected system, t:,~] In the eccentric bubble plume, there is the nonsymmetrical influence of the wall. Hence, its hydrodynamic characteristics may differ from those of the centric system. In the present work, we investigated the gas concentration, liquid velociLy, and gas velocity in an eccentric air/water plume of pilot scale. The results are reported in the following sections.
II.
EXPERIMENTAL TECHNIQUE
The experimental setup and procedure are the same as in the previous study of the centric plume.[U A schematic of the experimental setup is shown in Figure 1. The size of the polypropylene vessel approximates that of a 30 t ladle for steel. It has a 1600 mm i.d. and a 2250 mm height. The nozzle is located midway between the center and the wall (400 mm away from both), and its upper end is flush with the vessel bottom. The probe is attached to an x-y traversing table which is mounted at the top of the basin. The height of the water was 1800 ram, and the atmospheric pressure was 0.942 bar. The air temperature was taken as ambient room temperature, 20 ~ Gas fraction, bubble frequency, and gas velocity were measured with resistivity probes, and the liquid velocity was measured with a propeller flowmeter. The measuring procedure and the data processing have been described in detail in the previous publication.m The experimental conditions are listed in Table I.
III.
EXPERIMENTAL RESULTS OBTAINED ON THE LARGE SCALE MODEL
A fundamental feature of bubble plumes in liquids is the fluctuating character, both in time and space, of the plume properties. Figure 2 shows two examples of time records of gas fraction measurements. The method of spectral analysis was applied for the analysis. The procedure is explained in detail elsewhereY] It consists of several steps, namely, normalization of the signal-time relationship, autoeorrelation, and filtering for removal of noise and finally results in the power spectrum. In Figure 2(a), there is a si~al with unambiguous periodicity which was found in all the measurements up to a height of 600 ram. The peak in the power spectrum (lower diagram) is at 0.043 Hz. In other spectra for z < 600 ram, sometimes a second peak existed at about 0.090 Hz. With increasing height above 600 ram, the periodical oscillations of the gas fraction gradually disappeared. At z = 1600 ram, the spectra were as shown in Figure 2(b), indicating a tendency toward stochastic behavior. The very fast fluctuations are caused by the nonuniformity of gas discharge at the no~le and the slow fluctuations by the lateral wandering of the plume, respectively. A
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