An experimental analysis of the stability of the jet wiping process: Part I – Characterization of the coating uniformity

•Scaling laws for the Jet Wiping Process are derived in a one-way coupling framework.•The non-uniformities on the final film after wiping are characterized experimentally.•The wave characteristics are highly dependent on the jet to substrate standoff distance.•The results suggest a fundamental role of the jet confinement and a two-way coupling between the gas jet and the liquid. The jet wiping process is a continuous coating method that uses impinging gas jets to control the thickness of a liquid layer dragged by a moving substrate. This first part of a two-part article on the analysis of the process stability presents an experimental characterization of the achievable coating uniformity as a function of various design and operating parameters, including the nozzle opening width, stand-off distance, tilt angle and stagnation pressure, substrate speed and liquid properties. The process is reproduced on a dedicated laboratory model, instrumented with a Light Absorption (LAbs) test section for the 3D time-dependent reconstruction of the final coating film thickness. Several types of wave patterns are observed on the final coating film and characterized in terms of peak to peak wave amplitude and dominant frequency. The results are nondimensionalized following the scaling laws derived from the classical ‘one-way coupling’ analysis of the process. This approach, which assumes that the wiping capabilities of the jet flow are not influenced by the dynamics of the impinged liquid, is proven successful for the prediction of the average film thickness but inadequate for the scaling of the coating non-uniformity. This suggests that the dynamics of the final coat is mostly governed by the interaction of the liquid with the gas jet, investigated in the second part of the article.