Investigation on the Surface Vortex Formation During Mechanical Stirring with an Axial-Flow Impeller Used in an Aluminum
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NICAL stirring of aluminum melt is used in various processes. In melting or holding furnaces, the main goal of melt stirring is to homogenize the molten bath in content and temperature after adding scrap and master alloys, and to eliminate undesirable impurities and inclusions from it. It is a common practice to use chloride and/or fluoride fluxes during stirring operations.[1] Also, aluminum melt must be degassed before casting, and a rotor or impeller type facility is commonly used to inject inert and/or chlorine gas in the molten bath.[1] Therefore, in aluminum industry, the efficient control of mechanical stirring is of vital importance in stabilizing the plant operation and saving the process time. In the context of this background, mechanical stirring of aluminum melt has been studied so far. The recent studies can be categorized into two groups: (1) fluxing and gas bubbling in melting or holding furnaces, and (2) online degassing. The main results of these recent studies are reviewed below.
TAKUYA YAMAMOTO, WATARU KATO, and SERGEY V. KOMAROV are with the Graduate School of Environmental Studies, Tohoku University, Miyagi 980-8579, Japan. Contact e-mail: [email protected] YASUO ISHIWATA is with the Nippon Light Metal Co. Ltd., Shizuoka 421-3297, Japan. Manuscript submitted April 18, 2019.
METALLURGICAL AND MATERIALS TRANSACTIONS B
Bilodeau et al. (2001) evaluated the efficiency of flux treatment in an actual melting furnace experimentally and also conducted numerical simulation to predict the removal of impurities from the molten metal bath.[2] In their study, the experimental results were compared with numerical predictions, and a noticeable discrepancy between them was reported. Kiss and Bilodeau (2001) investigated the flow and bubble structure near an axial-flow rotor using water model experiments.[3] They found that the injected bubbles are fragmented and aligned in chains at the rear surface of rotor blades. Kerdouss et al. (2005) also investigated the flow and bubbles structure near the same rotor using a water model experiment and numerical simulation.[4] They found that the direction of discharge flow is varied due to the gas bubble movement. Flow patterns generated by different impellers were investigated in a water model of an aluminum melting furnace by Song et al. (2003), Chiti et al. (2004), and Bujalski et al. (2004).[5–7] Song et al. (2003) conducted Particle Image Velocimetry (PIV) measurement and multiphase flow simulation to investigate the flow pattern generated by a 30-degree pitched paddle impeller.[5] The experimental and simulated flow patterns were in a qualitative agreement with each other. Bujalski et al. (2004) investigated the effect of impeller shape on the mixing time using a water model experiment.[7] They found the optimal dimension of impeller shape and the relationship between the impeller rotational speed and mixing time. Later, the authors of the present study investigated the mixing time using a
scaled-down water model and numerical simulation,[8] the turbulent flow structure arou
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