Dynamics of the Jet Wiping Process via Integral Models

The jet wiping process is a cost-effective coating technique that uses impinging gas jets to control the thickness of a liquid layer dragged along a moving strip. This process is fundamental in various coating industries (mainly in hot-dip galvanizing) and is characterized by an unstable interaction between the gas jet and the liquid film. This interaction is of significant interest to industry and academia alike and results in wavy final coating films. To understand the dynamics of the wave formation, this work investigates the response of the liquid film to a prescribed set of disturbances in the impinging gas jet flow. In particular, we extend classic laminar boundary layer models for falling films to the jet wiping configuration, including the self-similar integral boundary layer (IBL) and the weighted integral boundary layer (WIBL) models. Moreover, we propose a transition and turbulence model (TTBL) to explore modeling extensions to larger Reynolds numbers and to analyze the impact of the modeling strategy on the liquid film response. These models were validated on a simple test case using Volume of Fluid simulations and are used to study the response of the liquid coat to harmonic and non-harmonic oscillations and pulsations in the impinging jet. The impact on these disturbances on the average coating thickness and wave amplitude is analyzed, and the range of frequencies yielding maximum disturbance amplification is presented.