論文ID: 12we048
The liquid phase mass transfer coefficient kL for the external loop airlift was investigated to elucidate a mechanism and degree for the gas-liquid concurrent, circulating liquid velocity uL to affect it. The approach was based on the Higbie model, i.e., kL∝ uS0.5 at a fixed average bubble diameter dB where the average bubble slip velocity uS was derived from the drift flux model. The uS and kL values were deduced to decrease in the order of the gas-liquid concurrent flow, batch liquid and countercurrent flow. The result was elucidated by variation of the bubble wake development with the turbulent liquid flow direction and rate, in addition to variations of liquid inertia and drag on individual bubbles. The observed kL, surpassing kLS for the single bubble and kL,BF for the bubble flow(BF), was increased by the enhancement effect of concurrent uL on kL through its preventing bubbles from clustering, coalescence and breakup. The kL values could reasonably be reproduced by the Higbie model in which the terminal rise velocity uBS was replaced by uS,BF = (gdB/2)0.5 for the BF. A factor F = kL/kL,BF derived from the above uS,BF-based equation for kL well reproduced the observed F.