Forcing microbubbles in microfluidics

The present thesis is a compilation of three studies in the field of microfluidic, more concretely, the generation of microbubbles and the effect that different applied forces have on them. A microbubble generation state of the art in terms of applications, employed fluids, working regimes and microfluidic devices is introduced in the first place. Several microfluidic devices: cross junction, TJunction, planar and axisymmetric flow focusing are compared with regard to their operational woking regime -bubbling, jetting or squeezing- and achievable microbubble size, as well as their fundamental advantages and limitations. In the second chapter, a novel swirl flow-focusing microfluidic axisymmetric device for the generation of monodisperse microbubbles at high production rates is presented. By forcing a swirl effect on the liquid stream, a more stable production, as well as a microbubble size reduction -up to 57% compared to the axisymmetric flow focusing-, is achieved due to the enhanced gas meniscus stability. The swirl is shown to expand the bounds of the jetting mode inhibiting the bubbling mode. An experimental study is performed for various blade angles -0º, 40º, 60º and 80º- and numerous gas to liquid flow rate ratios, validating previous numerical simulations and previous flow-focusing scaling law proposed by Gañán- Calvo [Gañán-Calvo, Physical Review E, 2004, 69(2), 027301]. Chips with 60º blades exhibit the best combination of swirl effect and robustness against perturbations. Chapter three is devoted to the active control of microbubble size on planar flow-focusing devices by means of an acoustic streaming or mechanical excitation. Few numerical studies have been reported so far, despite the invaluable information that computational analysis can through on this topic. In this chapter, the microbubble generation is numerically analyzed for an ample range of acoustic accelerations and frequencies and for several contact angles. A bubble volume change of 20% when sweeping between 25º and 120º was observed. The addition of an acoustic excitation showed a correlation between the frequency and the highest amplitude that the system can absorbed without collapsing. Likewise, bubble size increases with the excitation amplitude. A theoretical framework for the physics and parametric description of that tuning is also presented. Finally, the effect of the acoustic excitation, not on bubble generation, but on a pinned microbubble in the low-energy regime is experimentally analyzed. Here, the goal is not to modify the bubble size, but to characterize liquid properties based on the bubble oscillation for medical diagnosis application. The novel Digital Holographic Microscope (DHM) is used for measuring the bubble interface movement and an unwrapping and mode recognition code is specifically developed for this chapter. Modes shapes and resonance frequencies were identified and related to the liquid surface tension to obtain a surface tension approximation. At the moment, further noise-reduction procedures as well as a viscosity relation to the bubble oscillation are being developed

D 3. 3 Final performance results and consolidated view on the most promising multi -node/multi -antenna transmission technologies

This document provides the most recent updates on the technical contributions and research challenges focused in WP3. Each Technology Component (TeC) has been evaluated under possible uniform assessment framework of WP3 which is based on the simulation guidelines of WP6. The performance assessment is supported by the simulation results which are in their mature and stable state. An update on the Most Promising Technology Approaches (MPTAs) and their associated TeCs is the main focus of this document. Based on the input of all the TeCs in WP3, a consolidated view of WP3 on the role of multinode/multi-antenna transmission technologies in 5G systems has also been provided. This consolidated view is further supported in this document by the presentation of the impact of MPTAs on METIS scenarios and the addressed METIS goals.Aziz, D.; Baracca, P.; De Carvalho, E.; Fantini, R.; Rajatheva, N.; Popovski, P.; Sørensen, JH.... (2015). D 3. 3 Final performance results and consolidated view on the most promising multi -node/multi -antenna transmission technologies. http://hdl.handle.net/10251/7675

First Annual Workshop on Space Operations Automation and Robotics (SOAR 87)

Several topics relative to automation and robotics technology are discussed. Automation of checkout, ground support, and logistics; automated software development; man-machine interfaces; neural networks; systems engineering and distributed/parallel processing architectures; and artificial intelligence/expert systems are among the topics covered