The flow dynamical behaviors and characteristics of the aligned and staggered viscous pumps are numerically investigated by two-dimensional laminar model. The flow fluxes and driving powers of the pumps are calculated and compared in dimensionless quantities by considering the effects of pump type, Reynolds number, rotor eccentricity, and rotor spacing. The increase of Reynolds number can reduce the dimensionless flow flux and increase the dimensionless driving power, while the rotor eccentricity can enlarge the dimensionless flow flux and driving power The rotor spacing can also play an important role in the dynamical performance of the aligned and staggered pumps. As rotor spacing rises, the flow stream lines between the two cylinders can bend more smoothly, so the flow flux grows with the driving power dropping, and these phenomena mostly exist in the pump with small rotor spacing. On the other hand, the vortex between the two cylinders probably develops as rotor spacing rising. then the flow flux is reduced with the driving power increasing, and these phenomena mainly exist in the pump with large rotor spacing. According to the simulation results and mechanism analyses, the staggered pump with optimal rotor spacing has the best dynamical performance with the highest flow rate and low driving power. (C) 2010 Elsevier Ltd. All rights reserved