The profiles of gas holdup and bubble velocity depending on superficial gas velocity were investigated in an inner airlift reactor with a down tube and an annulus gas distributor.The experimental set-up was made of plexiglass with an inner diameter of 0.286 m and a height of 3.0 m.Air and tap water were used as gas and liquid phases

respectively.The results showed that the gas holdup increased with increasing superficial gas velocity within both inner and outer loops.The gas holdup in the inner loop

however

was much higher than that in the outer loop.The bubbles entering the inner loop from the outer loop could be neglected in the ranges of the operating conditions.When an annulus gas distributor and a down tube were installed in the conventional airlift reactor

the gas holdup increased and its distribution became uniform

which enhanced the interfacial area between gas and liquid phases and the turbulent intensity of multiphase flow.Therefore

the interphase transfer would be improved in the inner loop.Then

the profiles of gas holdup and bubble velocity were simulated by using the Euler-Euler model in the platform of ANSYS CFX10.0 software package and fair agreement between numerical and experimental data was obtained. These results implied that the CFD simulation based on the Euler-Euler model

accompanied with experimental measurement

could be used to develop and scale up this new kind of loop reactor.