Study on gas–liquid flow characteristics in stirred tank with dual-impeller based on CFD-PBM coupled model

Abstract

Study on gas–liquid flow in stirred tank with two combinations of dual-impeller (six-bent-bladed turbine (6BT)+six-inclined-blade down-pumping turbine (6IT D ), the six-bent-bladed turbine (6BT)+six-inclined-blade up-pumping turbine (6IT U )) was conducted using computational fluid dynamics (CFD) and population balance model (PBM) (CFD-PBM) coupled model. The local bubble size was captured by particle image velocimetry (PIV) measurement. The gas holdup, bubble size distribution and gas–liquid interfacial area were explored at different conditions through numerical simulation. The results showed that the 4 mm bubbles accounted for the largest proportion of 33% at the gas flow rates Q = 0.76 m 3 ⋅h −1 and 22% at Q = 1.52 m 3 ⋅h −1 for combined impeller of 6BT + 6IT U , while the bubbles of 4.7 mm and 5.5 mm were the largest proportion for 6BT + 6IT D combination, i . e . 25% at Q = 0.76 m 3 ⋅h −1 and 22% at Q = 1.52 m 3 ⋅h −1 , respectively, which indicated that 6BT + 6IT U could reduce bubble size effectively and promote gas dispersion. In addition, the gas holdup around impellers was increased obviously with the speed compared with gas flow rate. So it was concluded that 6IT U impeller could be more conductive to the bubble dispersion with more uniform bubble size, which embodied the advantages of 6BT + 6IT U combination in gas–liquid mixing.