In this paper a standard k-ε model is used to predict the turbulent flow generated by an axial impeller in a cylindrical baffled vessel. The model predictions successfully reproduce the three dimensional characteristics of flow

and are in good agreement with those obtained by PDA measurement.The simulation results show that the ratio of impeller diameter to tank diameter ( D/T )has a great effect on the flow pattern in a stirred tank.For the small diameter impeller

such as D =0 35 T

the primary circulation loop is smaller than the whole vessel size

a weak secondary circulation loop is formed in the upper region of the tank.With increasing impeller diameter

axial flow is enforced and the primary circulation loop is extended to the tank top and the secondary circulation in the upper region of tank disappears.The simulation results also demonstrate that the flow in front of baffles is different from the flow behind baffles for the impeller D/T =0 55.In front of baffles

axial flow dominates and only one circulation loop is formed.The flow pattern is approximately the same.Behind baffles

axial flow becomes weaker

and the fluid turns inward just above the impeller level.A small second recirculation loop is formed in the upper part of the vessel

and is directed downwards rather than upwards.