Rotary tubular membrane separators are widely used in recent years because of their high performance in separation. The flow field inside the separator was theoretically and experimentally studied.In the theoretical part

flow stability inside the separator was discussed and the critical Taylor numbers were deduced. In the experimental part

a particle image velocimetry (PIV) system was used to measure the flow field in the annular gap of the separator. Three cases were investigated:①no axial flow and no permeating flow; ②axial flow but no permeating flow; ③both axial and permeating flow. Finally

axial and radial velocity distribution in the annular gap was quantitatively studied. The experimental results were consistent with the theoretical analysis.