Fluid Mechanics of the Inspection of Pre-filled Medical Syringes

In this thesis, the process of the inspection of pre-filled syringes (PFS) is explored in the context of fluid flow and particle motion. The inspection of PFS is a key stage in ensuring drug safety and quality. This work combines computational modelling with experimental testing to understand the fluid dynamics of the inspection process and links this to particle flow within the PFS. The process of inspection involves the fluidisation of particles by spinning a PFS (spin-up) and suddenly stopping its rotation (spin-down), leading to flow features enabling particle lift. A series of computational fluid dynamics (CFD) simulations are developed in COMSOL Multiphysics to replicate the spin-up and spin-down phases used in industry. A custom-built experimental rig is also designed to reproduce real inspection conditions. Research focuses on how parameters such as Reynolds number, aspect ratio, and viscosity influence flow stability, jet formation, and particle movement.

The results show that during the spin-down phase, strong axial jets form within the syringe, creating a short but vital window when the particles become suspended. This is essential for vision systems to detect particles during inspection and it is found that higher Reynolds numbers and larger aspect ratios promote fluidisation, whereas higher viscosity dampens motion. By using simulations and experiments, operational maps are created to help manufacturers optimise inspection settings for different syringe types based on their aspect ratio. The findings have direct industrial relevance discussed in the thesis. The study also highlights directions for future research, including multi-particle simulations, 3D modelling, and enhanced imaging methods. Ultimately, this work bridges the gap between theoretical fluid mechanics and practical pharmaceutical inspection. Providing tools and insights that can improve safety, efficiency, and consistency in the production of pre-filled syringes.