1. Sevilla, A. and Gordillo, J. M. and Mart{\'{i}}nez-Baz{\'{a}}n, C. (2005) {Transition from bubbling to jetting in a coaxial air-water jet}. Physics of Fluids 17(1) https://doi.org/10.1063/1.1831312, 10706631, :C\:/Users/adrig/Desktop/PhD/Literature/1.1831312.pdf:pdf, 1912.03899, 1912.03899, arXiv, In this Brief Communication we study experimentally the flow regimes that appear in coaxial air-water jets discharging into a stagnant air atmosphere and we propose a simple explanation for their occurrence based on linear, local, spatiotemporal stability theory. In addition to the existence of a periodic bubbling regime for low enough values of the water-to-air velocity ratio, u = uw/ua, our experiments revealed the presence of a jetting regime for velocity ratios higher than a critical one, uc. In the bubbling regime, bubbles form periodically from the tip of an air ligament whose length increases with u. However, when u > uc a long, slender gas jet is observed inside the core of the liquid coflow. Since in the jetting regime the downstream variation of the flow field is slow, we performed a local, linear spatiotemporal stability analysis with uniform velocity profiles to model the flow field of the air-water jet. Similar to the transition from dripping to jetting in capillary liquid jets, the analysis shows that the change from the bubbling to the jetting regime can be understood in terms of the transition from an absolute to a convective instability. {\textcopyright} 2005 American Institute of Physics.
2. Oguz, Hasan N. and Prosperetti, Andrea (1993) {Dynamics of Bubble Growth and Detachment from a Needle}. Journal of Fluid Mechanics 257: 111--145 https://doi.org/10.1017/S0022112093003015, 14697645, :C\:/Users/adrig/Desktop/PhD/Literature/dynamics-of-bubble-growth-and-detachment-from-a-needle.pdf:pdf, Several aspects of the growth and departure of bubbles from a submerged needle are considered. A simple model shows the existence of two different growth regimes according to whether the gas flow rate into the bubble is smaller or greater than a critical value. These conclusions are refined by means of a boundary-integral potential-flow calculation that gives results in remarkable agreement with experiment. It is shown that bubbles growing in a liquid flowing parallel to the needle may detach with a considerably smaller radius than in a quiescent liquid. The study also demonstrates the critical role played by the gas flow resistance in the needle. A considerable control on the rate and size of bubble production can be achieved by a careful consideration of this parameter. The effect is particularly noticeable in the case of small bubbles, which are the most difficult ones to produce in practice. {\textcopyright} 1993, Cambridge University Press. All rights reserved.
3. Sevilla, A. and Gordillo, J. M. and Mart{\'{i}}nez-Baz{\'{a}}n, C. (2005) {Bubble formation in a coflowing air-water stream}. Journal of Fluid Mechanics 530: 181--195 https://doi.org/10.1017/S002211200500354X, 00221120, :C\:/Users/adrig/Desktop/PhD/Literature/bubble-formation-in-a-coflowing-airwater-stream.pdf:pdf, In this work, we present a detailed experimental study of the periodic formation of bubbles in an air-water coflowing stream, as well as a simple model to describe the process. The frequency of formation of bubbles was measured analysing a large number of images recorded with a high-speed camera for a wide range of experimental conditions and air-injection needle geometries. The analysis of the images indicated that the bubble-formation process consisted of two distinct stages, namely the ligament expansion stage, characterized by the radial growth of an air ligament left attached to the injection needle after the pinch-off of a bubble, and the ligament collapse stage, characterized by the formation of a neck at the tip of the injection needle which propagates downstream, at a velocity which is nearly the liquid velocity, until it collapses generating a new bubble. A simplified model, based on the Rayleigh-Plesset equation for a cylindrical geometry to determine the dynamics of the liquid stream and on Bernoulli's equation to determine the air pressure near the neck, has been proposed to estimate the duration of the ligament collapse stage, tcol. The experimental bubble-formation frequency, properly scaled with the breakup time given by the model, is shown to collapse onto the same curve for all the experimental conditions used here, indicating that our simple model seems to retain the main physical aspects of the process. {\textcopyright} 2005 Cambridge University Press.
4. Rodr{\'{i}}guez-Rodr{\'{i}}guez, Javier and Sevilla, Alejandro and Mart{\'{i}}nez-Baz{\'{a}}n, Carlos and Gordillo, Jos{\'{e}} Manuel (2015) {Generation of microbubbles with applications to industry and medicine}. Annual Review of Fluid Mechanics 47: 405--429 https://doi.org/10.1146/annurev-fluid-010814-014658, Drops,acoustics,biomedicine,bubbles,microfluidic devices,surfactants, 00664189, :C\:/Users/adrig/Desktop/PhD/Literature/annurev-fluid-010814-014658.pdf:pdf, We provide a comprehensive and systematic description of the diverse microbubble generation methods recently developed to satisfy emerging technological, pharmaceutical, and medical demands. We first introduce a theoretical framework unifying the physics of bubble formation in the wide variety of existing types of generators. These devices are then classified according to the way the bubbling process is controlled: outer liquid flows (e.g., coflows, cross flows, and flow-focusing flows), acoustic forcing, and electric fields. We also address modern techniques developed to produce bubbles coated with surfactants and liquid shells. The stringent requirements to precisely control the bubbling frequency, the bubble size, and the properties of the coating make microfluidics the natural choice to implement such techniques.
5. Ga{\ {n}}{\'{a}}n-Calvo, A. M. and Gordillo, J. M. (2001) {Perfectly monodisperse microbubbling by capillary flow focusing}. Physical Review Letters 87(27 I): 2745011--2745014 https://doi.org/10.1103/physrevlett.87.274501, 11800883, 00319007, :C\:/Users/adrig/Desktop/PhD/Literature/PhysRevLett.87.274501.pdf:pdf