Computational fluid dynamics (CFD) simulations were performed to study effects of the flow pattern on the mixing quality of floating solids in stirred tanks with up- and down-pumping pitched blade turbine (PBTU and PBTD). The variables about impeller design have influences in the flow pattern and four key ones, impeller diameter, clearance from tank bottom, blade angle and number, were investigated in this work. Euler-Euler multiphase model along with mixture k-epsilon turbulence model was adopted. The relative motion between rotating impeller and stationary baffles was modeled with the multiple reference frame (MRF) approach. The predicted results were compared and explained with the experimental or theoretical results in published literature. Qualitative and reasonable agreement was achieved.