The flow fields in a dual Rushton impeller stirred tank with diameter of 0.48 m(T)were measured byusing Particle Image Velocimetry(PIV).Three different size impellers were used in the experiments with diametersof D =0.33T,0.40T and 0.50T,respectively.The multi-block and 360°ensemble-averaged approaches were usedto measure the radial and axial angle-resolved velocity distributions.Three typical flow patterns,named,mergingflow,parallel flow and diverging flow,were obtained by changing the clearance of the bottom impeller above thetank base(C1)and the spacing between the two impellers(C2).The results show that while C1 is equal to D,theparallel flow occurs as C2≥0.40T,C2≥0.38T and C2≥0.32T and the merging flow occurs as C2≤0.38T,C2≤0.36T and C2≤0.27T for the impellers with diameter of D=0.33T,0.40T and 0.50T,respectively.When C2 isequal to D,the diverging flow occurs in the value of C1≤0.15T for all three impellers.The flow numbers of theseimpellers were calculated for the parallel flow.Trailing vortices generated by the lower impeller for the divergingflow were shown by the 10°angle-resolved velocity measurements.The peak value of turbulence kinetic energy(2tipk /V=0.12-0.15 or above)appears along the center of the impeller discharging stream.