A study on the air knife flow with Coanda effect

The coating thickness in hot-dip zinc galvanizing process is of practical importance in determining the quality of products and its control is often done using the gas wiping through an air knife system. Such a gas wiping method causes a technical problem of splashing from the strip edge to have a harmful effect on the performance of the galvanizing process and the product quality. The present study aims at investigating the effectiveness of Coanda nozzle to reduce the strip splashing problem. A blow-down wind tunnel has been used to experimentally investigate the detailed flow field near the exit of Coanda nozzle and on the strip edge. A computational work has been performed with the help of a computational fluid dynamics method. The three-dimensional, compressible Navier-Stokes equations have been solved using a fully implicit finite volume scheme. The results obtained show that Coanda nozzle effectively reduces the splashing problem, leading to improvement of the whole galvanizing process.