Simulation of entrainment of agglomerates from plate surfaces by shear flows

The entrainment process of agglomerates deposited on plate surfaces by shear flows was simulated using the three-dimensional modified discrete element method (mDEM) and influences of several factors on entrainment process were examined. In the case shear induced force is too weak, deposits are only deformed and particles are barely entrained, however, above some critical value particles are entrained by flows forming agglomerates. It was also clarified that the steric-bulky deposit undergoes the stronger hydrodynamic force and is easy to be entrained. There are two entrainment mechanisms corresponding to the parameter A s / A which indicates the relative strength of adhesive force between particle and plate surface to that between particles. In case of large A s / A where the adhesion between particle and plate surface is predominant, the number of entrained particles monotonically decreases as A s / A increases due to the enhanced binding force. By contrast for small A s / A , the number of entrained particles is not heavily dependent on A s / A due to the mechanism in which the upstream side of deposit is lifted and the deposit is deformed extensively then large agglomerates are entrained. The boundary between those two entrainment mechanisms exists at A s / A = 0.5 – 0.6 which is in good agreement with the theoretical prediction.