Stability and pressure drop of gas–liquid micro-dispersion flows through a capillary

• The rule of initial dispersion size of bubbles through a membrane was studied.
• The stability of bubbly flow in a capillary was directly studied by a CCD camera.
• The pressure drop of gas–liquid flow in horizontal capillary was studied.
• A model was developed to predict the pressure drop in gas–liquid coalescence system.

The stability and pressure drop of gas–liquid micro-dispersion flows through circular capillaries with an inner diameter of 1 mm and lengths from 10 cm to 100 cm were investigated. The gas phase was dispersed into the liquid phase through a microfiltration membrane with an average pore diameter of 5 μm to generate microbubbles and form gas–liquid microdispersion systems; the average size of the initial dispersion bubbles ranged from 70 to 115 μm. A CO2 absorption solution of ethylene glycol (EG) added to 2-amino-2-methyl-1-propanol (AMP) and nitrogen gas were used as the liquid and gas phases, respectively; (Sodium dodecyl sulfate) SDS was used as a surfactant. A video-imaging technique was also used to determine the flow characteristics in the capillaries. A capillary with a maximum length of 100 cm was demonstrated to produce a significant pressure drop of up to 500 kPa, which expanded the bubbles present in the flow and increased the flow velocity. The results of this study showed that bubble coalescence in gas–liquid microdispersion systems with SDS was not present but was significant in gas–liquid microdispersion systems without a surfactant. Additionally, two models were developed to predict the pressure drop in both gas–liquid systems with and without bubble coalescence.