Study On The Behavior Of Parallel Bubbles Coalescence In Non-Newtonian Fluids

It is essential to adequately understand of the process of parallel bubbles growth and coalescence characteristics for optimizing the gas-liquid design reactor. Level set and volume of fluid method(CLS-VOF) and high-speed video camera were adapted to research behavior of bubbles coalescence in different conditions Non-Newtonian fluids, and the behaviors of bubble break-up were studied in microchannel.A numerical simulation is performed to investigate the behaviors of coalescing bubbles from parallel nozzles in carboxyl methyl cellulose(CMC) solution using volume-of-fluid with level-set methods(CLS-VOF). This approach was validated by comparing with the experimental results. The bubbles coalescence mechanism is studied by observing images of bubbles captured by CCD camera in different conditions. The influences of the mass concentration of CMC solution, surfactant concentration(sodium dodecyl sulfate, SDS), gas flow rate, nozzles distance and nozzle diameter on aspect ratio are investigated, respectively. The results indicate that aspect ratio of bubbles increases with gas flow rate and nozzle diameter before bubbles coalescence, however, with no significant variety as CMC solution concentration, SDS concentration and nozzles distance. After bubble coalescence, aspect ratio increases with CMC concentration, SDS concentration and gas flow rate, while decreases with nozzle diameter.The reason for the parallel bubble coalescence is discussed. The results show that the prerequisite of bubbles coalescence is that the bubble contact time is larger than the required coalescence time and bubble coalescence is the result of interaction of internal and external flow. The impact of gas flow rate, liquid properties, surface tension and other factors on bubble coalescence probability is analyzed. The results show that the probability of bubble coalescence has significant difference at different flow rates; surfactant inhibits bubble coalescence; CMC promotes bubble coalescence, however, with no significant variety as nozzle diameter and nozzles distance.Bubble breakup behaviors are studied by CLS-VOF mothed in microchannel with different angle of outlet. The results indicate that: The neck thickness of bubble increases with vapor flow rate in the early process of bubble breakup under the same liquid flow rate. However, the neck thickness rapidly decreases with vapor flow rate addition. The neck thickness increases with the concentration of Polyacrylamide(PAM). The probability of bubbles breakup increases with bubble length, while decreases with angle of outlet microchannel.