Hydrodynamics of fluid flow approaching a moving boundary
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I. INTRODUCTION
MANY iron- and steelmaking-related industrial processes involve the passing of a wire, strip, or roller through the free surface of a liquid. One such example is the coating of a steel plate with an aluminum zinc alloy in a continuous strip-coating bath. In these processes, the steel plate is typically drawn through the bath at speeds between 0.5 and 2.0 m s21. The nature of the chemical bonding of the plate to the overlay ultimately determines the quality of the product, and, therefore, it is essential to understand all the factors influencing its formation. These include mass transfer, heat transfer, wettability, and flow patterns within the molten bath. Previous studies have shown that the thickness, nature, and uniformity of the intermetallic alloy layer are dependent on the process conditions present when the initial contact occurs between the steel strip and the molten coating.[1,2] A large body of work has been conducted for long contact times (i.e., 5 seconds); however, recent high-speed dip-coating experiments[3] have suggested that the wetting of the strip by the molten metal and the subsequent growth of the intermetallic layer are determined prior to the first 20 ms of contact. Therefore, an understanding of the flow in the immediate vicinity of the entry of the plate into the bath is important. This entry point corresponds to a moving contact line at which the gas, liquid, and solid phases meet. There have been many attempts at modeling the flow near a moving contact line under conditions of creeping flow. The original solution of Moffat[4] demonstrates the difficulties in these models, with classical assumptions resulting in unbounded stresses near the contact line. Various assumpGREG D. RIGBY, Research Engineer, and LES STREZOV, Research Leader, are with the Centre for Metallurgy and Resource Processing, BHP Minerals Development, Wallsend NSW 2287, Australia. CHRIS D. RIELLY, Professor, is with the Department of Chemical Engineering, Loughborough University, Loughborough, Leics LE11 3TU, United Kingdom. SCOTT D. SCIFFER, Research Associate, JOHN A. LUCAS, Senior Lecturer, and GEOFFREY M. EVANS, Associate Professor, are with the Department of Chemical Engineering, University of Newcastle, Callaghan NSW 2308, Australia. This article is based on a presentation made in the “Geoffrey Belton Memorial Symposium,” held in January 2000, in Sydney, Australia, under the joint sponsorship of ISS and TMS. METALLURGICAL AND MATERIALS TRANSACTIONS B
tions, including slip against the solid surface on a microscopic scale,[5,6] have been introduced to relieve this anomaly. Physical and computational modeling of overall stripcoating processes have also been conducted using smallscale water models[7,8] (with flow measurement using hotwire anemometry and laser doppler velocimetry techniques) and commercial computational fluid dynamics (CFD) codes[8,9,10] to produce three-dimensional representations of flows in a coating bath. However, these studies have not considered in detail the flow in the crucial re
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