Scaling Physical Model Study on Dynamic Accumulation of Bottom Dross in a Molten Zinc Pot

Abstract

A theoretical framework of similarity and its related experimental methods concerning scaling physical model are presented to investigate dynamic behavior of bottom dross in a zinc pot during the continuous hot-dip galvanizing process. Based on the similarity criteria of Froude number, turbulent Reynolds number, Shields number and particle Reynolds number, an analytical framework is developed to describe similarity of dross dispersion, transport and deposition in a stirred molten zinc tank. A complete set of experimental methods are suggested correspondingly. A 1/5 reduced scale model is adopted to study steady flow field, dynamic accumulation rules and stable shape of bottom dross. NaCl aqueous solutions and black particles of acrylonitrile butadiene styrene are employed as model fluid and bottom dross, respectively. The results show that two impact flows are the key factors in the formation of dross deposition morphology in the bottom of zinc bath. The first impact flow strikes bottom drosses located in the floor of tank and near the front wall and results in three impact craters for symmetric distribution. The other impact flow hits bottom drosses deposited blow the sink roll. A pair of pits with curved edges and a ridge between them are formed. The dispersed bottom drosses under impact are carried by the main circular flow and heaped up toward the back wall similar to a mobile dune. The greater the difference between current shape and steady state morphology of bottom dross, the more dross particles are scattered.