شبيه سازي عددي انتقال حرارت در فرآيند پوشش دهي ورق گالوانيزه

چكيده انگليسي :

Numerical Simulation of Heat Transfer in Jet wiping process Asghar Sadeghi a sadeghi@me iut ac ir May 10th 2010 Department of Mechanical Engineering Isfahan University of Technology Isfahan 84156 83111 Iran Degree M Sc Language Farsi Mohsen Saghafian saghafian@cc iut ac ir Abstract One of methods of galvanizing strip production is continuous hot dip coating In hot dip coating process a continuous steel strip is passing from bath of coating fluid zinc in result one or both of the steel sides are wetted The moving steel is located between a pair of plan air knife jets and consequently the excessive zinc returning to the bath by impinging air jets Gas jet wiping is a preferred method for controlling the final film thickness because it avoids physical contact between the coating film and the air jets The main parameters that control this process are the pressure distributions and shear stress distributions induced by the jet on the liquid surface Others depend on the process parameters such as standoff distance nozzle slot opening nozzle pressure and strip velocity and on the liquid properties The aim of this study is simulating the heat transfer in the jet wiping at galvanization process including the following steps 1 Computational study of impingement heat transfer under a turbulent slot jet Jet impingement is simulated via FLUENT The compressible air flow steady two dimensional ideal 2 gas and v f turbulence model are options used to simulate impingement air jet Jet impingement has two regions namely near jet region and far jet region In near jet region the air jet is more effective 2 Calculating thickness of coating molten zinc A Finite Difference CFD code is developed to predict coating thickness In this code one dimensional steady and laminar zinc fluid flow is solved Distribution of shear stress and pressure of air jet along the strip are necessary for prediction coating thickness also geometrical air jet details and molten zinc properties are needed In this stage velocity distribution and coating thickness of molten zinc are calculated 3 Calculating temperature distribution in steel and zinc metal and the prediction of the onset of solidification of molten zinc A Finite Volume CFD code is developed to solve energy equation The heat transfer includes three parts convection forced convection and free convection radiation and conduction In far jet region radiation heat transfer is the dominant mechanism In this stage the heat transfer coefficient velocity distribution and coating thickness of molten zinc strip velocity and molten zinc properties are necessary It s important that the solidification process is simulated as well in order to find the place where the solidification is started and the length of solidification completion In this stage effect of parameters such as strip thickness velocity distribution and coating thickness distribution the heat transfer coefficient etc are investigated The nucleation and growth of zinc grains during the solidification process depending on the rate of the heat transfer loss The solidification process is a critical step in the hot dip galvanization processes because of the heat transfer rate affects the size of grains Note also that the size of grains increases with decreasing heat transfer rate Key Words Heat transfer Jet wiping Solidification Galvanization

صادقي، اصغر

شبيه سازي عددي انتقال حرارت در فرآيند پوشش دهي ورق گالوانيزه

جت شويي , انجماد , گالوانيزه كردن