GOALI: Coating of Rotating Discrete Objects

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Coating of liquid films onto non-flat discrete objects arises in the manufacturing of a broad variety of products such as automobile and aerospace components, medical implants, three-dimensional printed parts, and foodstuffs. Coatings are often needed to protect or functionalize surfaces, or even to create the final product itself. It is an essential element in American manufacturing. This Grant Opportunity for Academic Liaison with Industry (GOALI) research promotes national prosperity in this critical area while developing new scientific insights into a complex problem. In contrast to liquid-film coating on flat substrates, liquid-film coating on non-flat discrete objects is considerably more challenging to understand at a fundamental level. For most applications, a coating of uniform thickness is desired. However, the complex interplay between forces arising from object rotation, object curvature, gravity, viscosity, surface tension, and inertia may lead to the growth of instabilities and thus coating non-uniformities. The overall objective of this project is to use a combination of theory, experiment, and industrial interaction to significantly advance fundamental understanding of the flow of liquid films on rotating discrete objects. The general principles that the work aims to establish provides a firm foundation for systematic design and optimization of industrial coating processes, thereby enabling future breakthroughs that address critical industry needs. Industrial outreach and involvement of undergraduate students from underrepresented groups complement the research activities.This project uses a combination of theory, experiment, and industrial interaction to significantly advance fundamental understanding of how liquid rheology, non-circular cross sections, and end-effects influence the flow of liquid films on rotating discrete objects. The theory involves finite-difference and finite-element simulations of generalized Newtonian liquids and viscoelastic liquids. The simulations yield predictions of coating-film thickness and stability limits as function of parameters characterizing rotation velocity, object shape, and, rheological properties. These predictions, along with asymptotic analysis of the underlying equations, are used to generate scaling laws that provide quick and accurate estimates helpful for industrial practitioners. The experiments involve flow visualizations using three-dimensional printed objects having non-circular cross sections and liquids having rheological properties consistent with the rheological models used in the simulations. Film-thickness variations and the onset of instabilities are inferred from the visualizations and compared to the theoretical predictions. The interplay between theory, experiment, and industrial interaction ultimately advances physical understanding and lead to general principles that can be applied in manufacturing processes involving the coating of discrete objects.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.