262578 CFD Approach for the Analysis of NON-Newtonian Polymeric Microparticles Production
We have developed a method to produce uniformly sized biocompatible microparticles from highly viscous non-Newtonian polymers. It is based on the growth of Rayleigh instabilities1, assisted by controlled vibration, in polymer fluid jets, which leads to the breakup of the jet into droplets. These are later stabilized giving rise to the solid microparticles. The system can process higher ranges of viscosity than conventional techniques, which results in a higher mechanical resistance of the produced particles. The technique has been characterised in a previous work, where a semiempirical model for predicting particle size was also proposed2.
In the present work a modelling approach, performed through Computational Fluid Dynamics (CFD) simulations (Ansys-Fluent ®), is assessed as a mean to validate the system behaviour. The simulations cover and aim to describe the jet breakup and the formation of the droplets under different conditions of superimposed vibrations. Simulation results and comparison with experiments and predictions based on the semiempirical model are discussed.
Close attention is paid to the nature of the used materials since most biocompatible polymers display non-Newtonian fluid behaviour to some degree. This makes the study of the system more difficult, in which non-Newtonian parameters play a key role and clearly influence the way the jet evolves. Thus, CFD has been also used as a way to test which non-Newtonian effects influence the system most. In addition, it also enables to determine viscoelastic parameters (such as relaxation and retardation times) which have not been possible to be obtained through experimentation. With this aim some constitutive equations were implemented and included to the standard equations already gathered by the commercial software via User-Defined-Functions (UDF). This programming tool is also used to establish the inlet boundary conditions as oscillating displacements.
This systematic approach is also useful in planning large scale systems and testing how changes in the materials and geometry of the nozzles affect the system. It is also of great convenience for the theoretical analyses in progress.
1. Rayleigh L. On the capillary phenomena of jets. Proc. R. Soc. London 1879;29.
2. Rodríguez-Rivero C, Del Valle EMM, Galán MA. Development of a new technique to generate microcapsules from the breakup of non-Newtonian highly viscous fluid jets. AIChE Journal. 2011;57(12):3436-3447.