BACKGROUNDTubular photobioreactors (TPBRs) have great potential in culturing microalgae, but their poor mixing properties make it difficult to increase the surface productivity. In this work, a TPBR with inserted self-rotating helical rotors, which have been under study for a decade, was designed. RESULTSThis paper aimed to show hydrodynamic behaviors of gas-liquid in a TPBR with inserted self-rotating helical rotors by computational fluid dynamics (CFD) and visualization experiments. It can be concluded that by assembling self-rotating helical rotors into the TPBR, very remarkable mixing and particle cycle frequencies were achieved. Besides, the influences of rotor lead and liquid inlet velocity on the swirl number, the gas and liquid average circumferential velocities, pressure loss, cell trajectories and shear stress were also investigated. The best choice was to select a rotor lead of 150 mm and a liquid inlet velocity of 0.4-0.5 m s(-1) for microalgae with strong shear force tolerance. Microalgae cultivation experiments verified that helical rotors had a positive effect on biomass productivity. CONCLUSIONThe results indicated that assembling the self-rotating helical rotors into TPBR was a feasible and effective method to improve the mixing performance and microalgae productivity. (c) 2017 Society of Chemical Industry