Behavior of micro-particles in fluid flow based on drag force modeling with shielding effect

Abstract

A discrete element method(DEM) is used widely for the simulation of micro particle behavior in the fields such as chemistry, water treatment and printing industry. The method simulates the individual particles motion from computing the each physical force. It is important to compute a drag force on individual particles because the flow effect is one of the major factors to affect behaviors of the particles. However it is difficult to predict the drag force on the aggregated particles because hydrodynamic interaction appears among the particles. Furthermore, the computational resource and time is limited to compute the hydrodynamic interaction of many particles. In this study, a simple model for the drag force acting on the N particles of aggregates in low Reynolds number was proposed. The present model predicts hydrodynamic interactions by considering the individual location and flow direction. The drag force model of two particles was obtained from exact solution. Furthermore, the model of N-particles was extended using scaling laws and curve fitting equations. The presented model was verified by computing the drag force acting on aggregates with a Filippov method. Verification was conducted in terms of fractal dimension of aggregates and number of particles. And the model was applied in DEM code. Also, a two-way coupling model between discrete element method(DEM) and lattice boltzmann method(LBM) was developed. The coupling model computes the hydrodynamic interaction among the particles using a cut off radius which is equivalent a cell volume size. It computes the hydrodynamic interaction in the inner cell with modeling and the outer cell with LBM calculation. The model was validated by computing the drag force around chain-arrayed particles Finally, Sedimentation simulation was conducted using the presented model. The sedimentation phenomena were considered with the particles aggregation, Brownian motion, and flow effect simultaneously. In terms of the settling velocity, it is observed that the aggregation effect increased settling velocity but the back flow effect decreased the settling velocity. A settling simulation result was compared with the one-way method and the two-way method.