K. Shahzad, W. Van Aeken, V.K. Kamyab, M. Mottaghi, S. Kuhn
Keywords: aggregation, adhesion, clogging, rigid suspensions, microfluidics, discrete element method (DEM), CFD-DEM simulation, OpenFOAM
Summary:Microfluidics has achieved a positive response in the industrial sector in the last two decades, i.e., due to its minute size plus control over all the chemical and physical properties at various flow rates (Re~1-10) and with less safety issues. However, there are also some challenges present with those devices, particularly microparticle wall deposition which initiates dendritic structures which end up clogging the whole microchannel or microfluidic device. We develop numerical solvers to study and understand the phenomena of aggregation and clogging of rigid microparticles suspended in a Newtonian fluid passing through a straight microchannel. Initially, we use a time-dependent one-way coupling Discrete Element Method (DEM) technique to simulate the movement and effect of adhesion on microparticles in 2D & 3D. It is a state-of-art tool whose script is written in Fortran. The aggregation and deposition behavior of particle-particle and particle-wall contacts are investigated by varying the Reynolds number and adhesion parameter in a non-periodic channel. The reason for selecting non-periodic channels was to replicate and achieve the flow condition as experienced in a microfluidic device. The contact mechanics between particle-particle interactions was implemented by using the Johnson-Kendall-Roberts (JKR) theory of adhesion. In addition, we employ a two-way coupling (CFDEM coupling) approach, where discrete solvers provide the solution for the DEM part by solving the equation of motion for each particle, and passing the resulting force fields as source term in the momentum equation to a continuous solver, which then solves the Navier-Stokes equations using CFD tools in OpenFOAM to calculate the resulting flow fields around the particles. We will describe the one and two-way coupling techniques in detail, and we will discuss the insight gained by predicting wall deposition and clogging behavior in microfluidic devices. In addition, results in term of microstructures, aggregates percentage and spatial and temporal evaluation of aggregates in 2D & 3D will be compared, respectively.