A coupled level-set/volume-of-fluid method, under the consideration of the rheological characteristics of a fluid, is employed to investigate numerical coalescence deformation of bubble pairs generated at two adjacent nozzles in carboxymethyl cellulose aqueous solutions. The satisfactory agreement between numerical results and experimental measurements proves the validity of this approach in predicting the surface evolution of bubbles. Simulated results show that the bubble coalescence process involves four stages of independent growth, rapid mergence, radial expansion, and vertical stretching. The various effects of surfactant concentration, gas flow rate, nozzle spacing, and nozzle diameter on the aspect ratio depend greatly on each coalescence period.

Bubble breakup in a four-branched microchannel with carboxymethyl cellulose (CMC) solution was investigated by an improved coupled level set and volume of fluid (CLSVOF) method based on consideration of the rheological characteristic of the fluid. The validity of the numerical approach was satisfactorily verified by comparing with the experimental results. The regime and pattern of bubble breakup were evaluated by analyzing the evolution of bubble morphology. The effects of gas velocity, solution concentration, and subchannel width on daughter bubble length were examined, respectively. The results indicate that three split regimes at the branch comprising expansion, squeezing, and pinch-off stage and three flow patterns including long slug, short slug, and bubble flows can be observed. Daughter