(380i) Simulations of Particle-Laden Flows in Microchannels

Microreaction engineering offers many advantages over conventional batch reaction systems commonly used in the pharmaceutical and specialty chemicals industries. The increased surface-to-volume ratio enhances the mass and heat transfer coefficients, thus improving efficiency and control. Despite the advantages of microreactors, their small dimensions also pose challenges. For example, the presence of particulate matter can quickly lead to clogging and permanently damage microchannels.

We developed a numerical tool to predict particle formation and agglomeration to study clogging in microsystems. This tool can be used to gain deeper insight into the underlying processes governing clog formation and help identify critical parameters. In addition, this tool enables process parameter-testing for adaption to microstructured devices.

For this, we used a coupled computational fluid dynamics (CFD) / discrete element method (DEM) approach. The DEM solver (LIGGGHTS) handles the equation of motion for each particle, while the CFD solver (OpenFOAM) solves the Navier-Stokes equations describing the fluid flow. The coupling software (CFDEM coupling) computes momentum exchange between particles and fluid. In the DEM solver, we implemented a contact model based on the JKR model [1] to accurately resolve particle-particle and particle-wall collisions.

As a test case, we investigated the precipitation and agglomeration of hydroxyapatite in a microchannel. Using the material properties of hydroxyapatite particles and the process parameters set in previous experimental studies [2], we investigated their effect on agglomeration size and distribution in time and position. The Young’s modulus was seen to have a great effect on whether stable agglomerates were formed.

Our previous experimental study [2] also showed an effect of dispersed inert gas bubbles on the polydispersity. Towards this end, we also address the three phase modelling (gas, particle and fluid) on the microscopic scale. For this, we developed a void fraction model which enables to simultaneously simulate large size bubbles and small size particles, respectively. Using the developed algorithm, we will predict particle deposition on bubbles and their behaviour in microfluidic devices. In addition, results in terms of bubble-particle aggregates percentage, and spatial and temporal evaluation of bubble-particle aggregates in 3D will be presented.

References

1. Johnson, K. L., K. Kendall, and D. Roberts. Surface Energy and the Contact of Elastic Solids. Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences, 1971. 324(1558): p.301- 313.

2. Castro, F., S. Kuhn, K. Jensen, A. Ferreira, F. Rocha, A. Vicente, and J. A. Teixeira. Process intensification and optimization for hydroxyapatite nanoparticles production. Chemical Engineering Science, 2013. 100: p. 352-359.