Bubbling Behaviour in Molten Metals

Abstract

Recent cineradiographic observations of gas injection into liquid metals plus bubble frequency measurements are used to develop a sequential mechanism for bubble growth and release from non-wetted nozzles at low gas flow rates. The bubble volumes at release are consistent with results in iron-carbon alloys over a wide range of variables, and are much larger than would be expected on the basis of aqueous systems. This is because all previous work in aqueous systems has been conducted with wetted nozzles. Paraffin was used as a non-wetting nozzle to simulate pyrometallurgical situations and the bubbles then spread across the nozzles in a similar manner to that for liquid metals. However, bubbles were still much smaller than those found in metallic systems. The implications of these findings on water modelling of pyrometallurgical gas injection operations are discussed.Resume-Des observations cineradiographiques recentes de l'injection de gaz dans les metaux liquides ainsi que des mesures de frequence des bulles sont utilisees pour developper un mecanisme sequentiel de la croissance et du detachement des bulles a partir de l'extremite de lances non-mouillees et pour de faibles debits de gaz. Lors du detachement, les volumes des bulles sont consist ants avec ceux obtenus pour des alliages fer-carbone dans un vaste domaine de variables, et sont beaucoup plus importants que ceux auxquels on pourrait s'attendre en se fondant sur les systemes aqueux. Ceci parce que tous les travaux precedents faits sur les systemes aqueux ont ete conduits avec des extremites de lances mouillees. Pour simuler les conditions pyrometallurgiques, la paraffine fut utilisee comme lance non-mouillante et les bulles s'etendaient alors d'une maniere semblable a celIe observee pour les metaux liquides. Cependant, les bulles etaient encore beaucoup plus petites que celles trouvees dans les systemes metalliques. Les implications de ces resultats sur les modeles a. eau des operations pyrometallurgiques d'injection de gaz sont discutees.Over the past 20 years, a considerable number of studies have been made concerning the formation and release of gas bubbles from nozzles submerged in aqueous and other low temperature liquids. As a result, at least twenty-five models [1] have been developed to account for the phenomena observed. These models have generally included such parameters as inside nozzle diameter, liquid density, viscosity, surface tension, gas velocity and density, on bubble size and frequency.While process metallurgists are also keenly interested in submerged gas bubble/jetting systems because of their importance in pyrometallurgical reactors, the opacity of their melts and the generally high temperature environments have tended to preclude many of the visual observations possible with aqueous systems. As a consequence, and since low temperature aqueous models are so much more convenient and accessible to experimentation, many metallurgical process studies have been made using low temperature analogues.In the present work, mechanisms for bu...

A Study of Spouts on Bath Surfaces from Gas Bubbling: Part II. Elucidation of Plume Dynamics

“…In the following discussion, it will be shown that the correlations for void fraction that other workers have developed using the modified Froude number are very similar to Eq. [29]. Therefore, this equation is preferred because it is based on Q * , which is related to Fr 0 L .…”

“…[13]). Equation [29] suggests that, in the buoyancy region of the plume, the void fraction is solely a function of the gas flow rate, Q, and the distance, z, and is not influenced by parameters such as the orifice diameter and the physical properties of the gas-liquid system. In order to verify the adequacy of Eq.…”

“…The present work has shown that the area-averaged void fraction is simply a function of Q * , Eq. [29]. As discussed previously, the Froude number based on the ladle height is related to Q * , as outlined in the Appendix.…”

“…A further problem with the modified Froude number is that, for porous plug injection, the nozzle diameter is difficult to define, because small bubbles are formed at each pore and may coalesce into larger bubbles before release from the plug surface. [29] The void fraction in the plume has been widely correlated with the modified Froude number. The present work has shown that the area-averaged void fraction is simply a function of Q * , Eq.…”

“…In order to verify the adequacy of Eq. [29], a comprehensive analysis of the available literature data have been carried out, and the results are plotted in Figure 6. These data represent an extremely wide range of experimental conditions, and it is clear that they are unified in an acceptable manner.…”