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A STUDY ON THE FLOW CHARACTERISTICS OF AIR-KNIFE USING A CONSTANT EXPANSION RATE NOZZLE  

Lee, Dong-Won ((주)STX엔진 엔지기술연구소)
Kang, Nam-Cheol (경북대학교 기계공학부)
Kim, Guen-Young (POSCO 기술연구소)
Kwon, Young-Doo (경북대학교 기계공학부)
Kwon, Soon-Bum (경북대학교 기계공학부)
Publication Information
Journal of computational fluids engineering / v.13, no.4, 2008 , pp. 1-7 More about this Journal
Abstract
In the process of continuous hot-dip galvanizing, it is well known that the gas wiping through an air knife system is most effective because of its uniformity in coating thickness, possibility of thin coating, workability in high speed, and simplicity of control. However, gas wiping used in the galvanizing process brings about a problem of splashing at the strip edge above a certain high speed of process. It is also known that the problem of edge splashing is more harmful than that at the mid strip surface. For a given liquid(of a certain viscosity and surface tension), the onset of splashing mainly depends upon the strip velocity, the gas-jet pressure, and the nozzle's stand-off distance. In these connections in the present study, we proposed three kinds of air knife system having nozzles of constant expansion rate, and compared the jet structures issuing from newly proposed nozzle systems with the result by a conventional one. In numerical analysis, the governing equations are consisted of two-dimensional time dependent Navier-Stokes equations, and the standard k-${\varepsilon}$ turbulence model is employed to solve turbulence stress and so on. As the result, it is found that we had better use the constant expansion-rate nozzle which can be interpreted from the point view of the energy saving for the same coating thickness. Also, we better reduce the size of separation bubble and enhance the cutting ability at the strip surface, by using an air-knife having constant expansion-rate nozzle.
Keywords
Gas Wiping; Air-knife; Hot-dip Galvanizing; Impinging Jet;
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