De Rosa, Stefano (2024) Modelling and simulation of multiphase fluid dynamics for industrial applications. [Tesi di dottorato]

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Abstract

Performing experiments in some industrial fields can be challenging because of the dimensions of the plants and because of the impossibility of interrupting the production line for long periods to carry the experimental campaigns. Computational Fluid Dynamics (CFD) can hence be a useful tool to improve the knowledge concerning industrial problems and helping optimise production lines. This thesis details the application of CFD to reproduce relevant multiphase problems in different industrial fields: production of glass artifacts, metallurgy and additive manufacturing. Each of the different problems is analysed in detail, posing particular care on their modelling, on the mathematical model used and the hypothesis and approximations chosen to simplify them, making them numerically solvable within the possibilities of the available computational resources. The implementation of said models in the simulations is also described in all of its parts, justifying each time the choice of the most appropriate software tools used. Finally, the results of the simulations are shown and commented, comparing them with experiments or with data from scientific literature when possible. The investigated problems concern the production of glass vials, the reproduction of a model of a steel ladle and the application of additive manufacturing techniques in 3D printing. Glass vials are widely used to store pharmaceutical products such as vaccines, these vials are produced through a thermoforming process that starts from glass tubes and proceeds through several production steps such as heating, mouth and shoulder forming, cutting, flame drilling, case back forming. The correct design of the thermoforming process is of crucial importance to guarantee high reproducibility of the vials, long-term stability and adequate shelf-life of the stored medicines, while reducing the operational costs. All the steps in this process line were modelled and simulated, to achieve an optimal design of the entire production line. Direct Numerical Simulations were then performed on a model conical steel ladle to replicate an experimental campaign found in literature, addressing both the hydrodynamics and the mass transfer of a tracer from the steel equivalent phase to the slag equivalent phase. Finally, CFD simulations and experiments were employed to evaluate the effect of the die swell phenomenon in printing processes of commercial 3D printers with polylactic acid (PLA) as the extruded material. The simulations in this thesis were performed with various software tools, both commercial and open source ones: Ansys Fluent, Comsol Multiphysics, OpenFoam and Basilisk. The modelling addressed momentum, mass, heat and species transfer, treating two and three phase flows with different approaches and dealing with turbulence, chemical reactions and complex fluids.

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