(98p) Theoretico - Experimental Based Design of a Fan Jet Nozzle for Microparticle Production Using Non Newtonian Fluids
Particle size is one of the key parameters for chemical and biomedical purposes when producing microparticles. Many current and new applications in this field are based on the breakup of liquid jets. In particular we deal with viscous polymeric solutions where the control of the particle size is carried out by the proper hydrodynamics of the jet generated. The hydrodynamics is mainly governed by the combination of the rheology of the polymer and the physical design of the nozzle. On the one hand, the microparticle properties must meet certain characteristics depending on the final use (i.e. biocompatibility, biodegradability, mono modal particle size distribution, particle strength when formed, etc.) defining the type of polymers used. On the other hand, the design of the nozzle determines the stresses, and consequently the breakup, on the jet.
The basic geometry of a fan-jet nozzle consists of a pipe that guides the liquid into a gas chamber just before the exit. This chamber is responsible for the air focusing effect on the liquid jet. The gas-liquid interaction generates instabilities into the jet that determine droplet (size) and particle dispersion. Typically, the nozzle designs, this is their geometrical features, are fixed and the operating parameters are reduced to the air and liquid pressures together with the liquid properties [1-4].
In this work we have used a fan jet nozzle with a new design done by the group. It has a variable height for the injection point for the liquid into the gas chamber in order to be able to vary the stream lines of the gas-liquid contact. We used high speed video techniques (Phanton v-310), laser particle measurement, and a proprietary pressure control design to investigate on the nozzle design that allows controlled particle size and jet break up. The study has two parts. First we evaluate jet stability as function of the gas – liquid stream lines and pressure patterns, in order to determine the break up characteristics of the jet as function of the liquid phase and the operating conditions for different positions of the liquid injection. Second, we evaluate how this translates into particle size by recovering the droplets in a Barium Chloride aqueous solution. We use a range of viscous Non-Newtonian polymeric solutions, whose rheological behavior is determined in the lab and are characterized using Carreau model.
From the experimental point of view, in terms of jet instabilization, we correlate the operating conditions with the break up period, length and the amplitude of the wave generated. For long oscillating periods generated on the jet, the elasticity of the liquid solution maintains the stability of the jet while for shorter periods; the jet breaks up into droplets. Furthermore, pulse regime was also identified. With respect to nozzle design, there is an injection location where the particle size obtained is minimum, but this minimum is more pronounced for larger pressure difference between the gas and the liquid phases.
We follow a hybrid experimental and simulated based approach with ANSYS –FLUENT® to validate the flow pattern in the chamber and the jet break up. CFD analysis is also being carried out to evaluate the process towards quicker nozzle design and optimization. We simulate the liquid flow through the pipes, the air flow inside the gas chamber, the contact between both phases and the instabilization of the liquid jet (primary break-up) based on an Euler-Euler approach. This part of the study allows for evaluating the effect of location of the injection point on the pressure and velocity patterns on the jet. On the other hand the second breakup is modeled using a Lagrange –Euler approach to account for the final particle size.
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 Nogareda, J, Rodríguez-Rivero, C., Martín, M, E.M.M. Del Valle, M.A. Galán, Non Newtonian CFD modeling of drops generated through fan jet nozzles for biomedical applications (2013) Rev. Submitted.