Concentric-tube airlift bioreactors Part II: Effects of geometry on liquid circulation

Liquid circulation velocity was investigated in three concentric-tube airlift reactors of different scales (RIMP, VL=0.07 m3; RIS-1, VL=2.5 m3; RIS-2, VL=5.20 m3). The effects of top and bottom clearance and resistance in flow pathway at downcomer entrance on the riser liquid superficial velocity, the circulation time, the friction coefficient and flow radial profiles of the gas holdup and the liquid superficial velocity in riser, using water-air as a biphasic system, were studied. It was found that the riser liquid superficial velocity is affected by the analyzed geometrical parameters in different ways, depending on their effects on the pressure loss. The riser liquid superficial velocity, the friction coefficient and the parameters of the drift-flux model were satisfactorily correlated with the bottom spatial ratio (B), gas separation ratio (Y) and downcomer flow resistance ratio (Ad/AD), resulting empirical models, with correlation coefficients greater than 0.85.