Bubble formation on submerged micrometer-sized nozzles in polymer solutions: An experimental investigation

This research presents detailed formation of air bubbles on different submerged micrometer-sized nozzles in Newtonian and non-Newtonian fluids. An experimental study is performed using the high-speed camera on three nozzles with diameters of 150, 450, and 600 mu m under relatively low gas flow rate conditions (0.1 similar to 1 ml/min). Distilled water and various concentrations of Carboxymethyl cellulose (CMC) aqueous solutions are utilized as the continuous phase for each type of fluid. Different characteristics of the bubble formation such as volume change, frequency, height, maximum width, and instantaneous contact angle are obtained using an image processing technique and the Young-Laplace equation. Effect of different parameters including gas flow rate, nozzle diameter, concentration, and rheological properties of the continuous phases are investigated. Also, a detailed dynamic force analysis is performed to survey the role of fluid properties on the effective forces. The force balance reveals that the surface tension force is dominant in the smallest orifice, while its influence decreases as the orifice diameter increases. Moreover, it was observed that the drag and hydrostatic forces have relatively noticeable contributions in this low gas flow rates. Furthermore, results show that under the conditions of this research, the characteristics of the bubble are weakly dependent on the gas flow rate. On the other hand, the concentration of the CMC and the rheological behavior of the non-Newtonian fluids so-obtained have a significant influence on bubble formation process. Also, observations made and predictions done as to the bubble's curvature (say, based on Young-Laplace equation) suggest that the necking phenomenon does not exhibit itself at the top of the nozzle in non-Newtonian liquids flowing through micron-sized nozzles.