Observing Nitrogen Bubbles in Liquid Zinc in a Vertical Hele-Shaw Cell
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INTRODUCTION
MANY pyrometallurgical processes are carried out in bubble column reactors that rely on specific interactions between gas bubbles and a metal melt. Yet, the understanding of the behavior of such bubbles is still limited.[1] This can mainly be attributed to the opaqueness of metals, which prevents direct visual observations of the flow phenomena. Therefore, most experiments on the hydrodynamics of gas injection in metallic systems rely on observations in equivalent water models.[2] Unfortunately, because of physical and chemical differences between aqueous systems and liquid metals, this type of experiments cannot always provide highly detailed descriptions of individual bubbles.[3,4] Nevertheless such descriptions are needed to study the BART KLAASEN, formerly Researcher with the Research Group for High Temperature Processes and Industrial Ecology, Department of Metallurgy and Materials Engineering, KU Leuven, Kasteelpark Arenberg 44, 3001 Leuven, Belgium, is now Project Leader with the Umicore Group Research & Development, Umicore, Watertorenstraat 33, 2250 Olen, Belgium. Contact e-mail: [email protected] FREDERIK VERHAEGHE, Professor with the Research Group for High Temperature Processes and Industrial Ecology, Department of Metallurgy and Materials Engineering, KU Leuven, is also Project Leader with the Umicore Group Research & Development, Umicore. BART BLANPAIN, Professor, is with the Research Group for High Temperature Processes and Industrial Ecology, Department of Metallurgy and Materials Engineering, KU Leuven. JAN FRANSAER, Professor, is with the Research Group for Materials with Novel Functionality, Department of Metallurgy and Materials Engineering, KU Leuven, Kasteelpark Arenberg 44, 3001 Leuven, Belgium. Manuscript submitted December 21, 2013. METALLURGICAL AND MATERIALS TRANSACTIONS B
complex interactions between hydrodynamic and thermokinetic phenomena at a mesoscopic scale. After all, these interactions determine the behavior of individual bubbles in particular and the mass and energy transfer between the phases in general. Therefore, experimental efforts to quantify the mesoscopic properties of bubbles directly in liquid metals should not be abandoned, if only to validate modeling efforts.[5] To overcome the limitations imposed by the opaqueness of metals, various techniques have been applied in the past. An overview can be found in Reference 6. However, to the knowledge of the authors, only two studies report a visualization of the overall shape of a gas bubble in a bulk metal melt. Firstly, there is the work of Saito et al. on a low melting Bi-Pb-Sn alloy using high-frame-rate neutron radiography.[7] Secondly, Iguchi et al. observed vertical bubble shapes in a similar alloy using a multineedle intrusive electroresistivity probe.[8] Unfortunately, the resolution of these approaches is limited, and no applications at high temperatures are reported. Therefore, as an alternative approach, the current authors recently suggested to study gas injection in liquid metals under quasi-2D flow cond
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