The breakup of bubbles into jets during submerged gas injection
- PDF / 1,167,141 Bytes
- 7 Pages / 603.28 x 783.28 pts Page_size
- 95 Downloads / 199 Views
I.
INTRODUCTION
GAS injection is an integral feature of metallurgical processes, such as steelmaking, copper converting, and aluminum refining, to name a few. In most cases, the gases are injected at high velocities to carry out the refming reactions quickly. Accurate knowledge of the flow regime is important for several reasons: (1) the contacting pattern controls the interfacial area for reaction and, hence, the refining rate; (2) the flow regime governs the pattern of refractory erosion adjacent to the tuyere; (3) the penetration of liquid metal back into the tuyere is determined by the flow pattern; and finally (4) there is great interest in the intensification of metallurgical reactors, that is, to carry out reactions faster in smaller reactors; thus, fluid flow issues become dominant in design. As will be discussed in the next section, the most important transition is the one from bubbling to jetting. Following this review of the literature, a new criterion based on instability, which results in the formation of small droplets and bubbles to make a jet, is presented. Previous work is re-evaluated in light of the newly proposed criterion, and it appears to provide a reasonably consistent explanation for most observations.
Y.-F. Z H A O , Graduate Student, and G.A. IRONS, Professor, are with the Department of Materials Science and Engineering, McMaster University, Hamilton, ON L8S 4L7, Canada. Manuscript submitted December 11, 1989. METALLURGICAL TRANSACTIONS B
II.
REVIEW OF THE LITERATURE
At very low gas flow rates, the volume of bubbles formed at nozzles is governed by a force balance between surface tension holding the bubble to the circumference of the nozzle and buoyancy forces acting on the bubble at release: Vb -(pg -
pg)g
[1]
For wetting systems, such as water, the bubbles are seen to form at the inner nozzle diameter, whereas for nonwetting systems, such as liquid metals, the bubbles spread to the outer diameter, t1'2] Except for some porous plug applications, the flow rates are well below commercial flow rates. This regime is mentioned because it is the only one in which surface tension has been recognized to play a significant role. At higher flow rates, the inertia of the liquid is the principal restraining force preventing the bubble from lifting from the nozzle. Davidson and Schuler t3j were the first to apply the concept of "added" or "virtual" mass to quantify the amount of liquid which must be accelerated. From their analysis, the volume of the bubble in an inviscid liquid is given by V b =
1.378Q12g
-0'6
[2]
There have been many investigations of bubble formation; for reviews, see Kumar and Kuloor [41 and Clift e t a l . m Several investigators have developed two-stage models of bubble growth to better simulate the observed behavior in which the bubbles are initially spherical and then become elongated before release. These models VOLUME 21 B, DECEMBER 1990 - - 997
provide only marginal improvements in the prediction of bubble volume compared to Eq. [2], particularly considering
Data Loading...
