Numerical modelling and experimental analysis of surface cleaning with rotating impinging jets

Impinging jets are widely used in the surface processing industry due to their high mass transfer capabilities in the near wall region. The current work concerns with numerical modelling of thin film removal from surfaces, both moving and stationary. The process of film removal from impinging jets is more often a multiscale problem where the jet and thin film are present at different scales. This poses a difficulty in using the conventional Volume of Fluid (VoF) model for modelling the process. The reason being the requirement of a very fine mesh in order to resolve the thin film which increases computational costs and time. Here, the multiscale problem is transformed to a multi-region problem by segregating the whole domain into impinging jet and thin film regions. The thin film is not resolved but modelled in the surface normal direction with the thin film theory. The momentum from the jet is then modelled as source terms in the thin film equations to acknowledge the presence of impinging jets in the film region. The calculation of source terms which are the hydrodynamic forces acting at the interface further provides possibilities of model reduction. The numerical models are applied to a novel Cleaning in Place machine which involves the use of rotating impinging jets for film removal from moving surfaces. Two numerical models are developed. First, a semi-empirical model based on theoretical aspects of jet dynamics and thin film theory. Second model is a more generic model developed based on one way coupling between the Volume of Fluid method solved on a finite volume grid and thin film theory solved on a finite area mesh. The semi-empirical model and the VoF-thin film model are in good agreement with the experimental results qualitatively.