Investigation of Gas Hold-up and Bubble Behavior in a Split-Cylinder Airlift Reactor: Pseudo-Plastic Non-Newtonian Fluids

In this research, the effect of carboxy methyl cellulose (CMC) addition into pure water as pseudo-plastic non-Newtonian fluid and its concentration on bubble diameter and gas hold-up were investigated. For this purpose, four different concentrations of CMC (0.05, 0.1, 0.15 and 0.2 w/v%) as the non-Newtonian fluid and five different superficial gas velocities (0.2, 0.4, 0.6, 0.8 and 1 cm/s) as the gas phase were examined in an airlift reactor. Bubble size distribution in the airlift reactor was measured by photography and picture analysis at various concentrations of CMC and various velocities of gas. Increasing in gas velocity created a wider bubble size distribution and thereby an increase in bubble diameter and gas hold-up in both riser and down-comer. However, the bubbles diameter in pure water was larger than those of the CMC solutions (in the riser and down-comer), but CMC concentration enhancement increased bubbles diameter and gas hold-up in the down-comer. Bubbles diameter expansion in the riser by CMC concentration enhancement took place from concentrations of 0.05 to 0.15 (w/v)% and then it suddenly decreased. Furthermore, gas hold-up decreased from concentrations of 0.05 to 0.15 (w/v)% and increased at concentration of 0.2 (w/v)%. The gas hold-up increases (more than that in the concentrations of 0.1 and 0.15%) when bubbles diameter decreases in concentration of 0.2%. The overall gas hold-up trend was similar to the gas hold-up in the riser.