Ingeniería Aeroespacial y Mecánica de Fluidos

URI permanente para esta comunidadhttps://hdl.handle.net/11441/11331

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Examinando Ingeniería Aeroespacial y Mecánica de Fluidos por Materia "AC electric field"

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    Breakup length of AC electrified jets in a microfluidic flow‑focusing junction
    (Springer, 2015-06) Castro Hernández, Elena De; García Sánchez, Pablo; Tan, Say Hwa; Gañán-Calvo, Alfonso M.; Baret, Jean-Christophe; Ramos Reyes, Antonio; Universidad de Sevilla. Departamento de Ingeniería Aeroespacial y Mecánica de Fluidos; Universidad de Sevilla. Departamento de Electrónica y Electromagnetismo; European Research Council (ERC); Ministerio de Economía y Competitividad (MINECO). España; Junta de Andalucía
    Electroactuation of liquid-liquid interfaces offers promising methods to actively modulate droplet formation in droplet-based microfluidic systems. Here, flow-focusing junctions are coupled to electrodes to control droplet production in the well-known jetting regime. In this regime, a convective instability develops leading to droplet formation at the end of a thin and uniform, long liquid finger. We show that in AC electric fields the jet length is a function of both the magnitude of the applied voltage and the electrical parameters such as the frequency of the AC field and the conductivity of the dispersed phase.We explain that dependency using a simple transmission line model along the liquid jet. An optimum frequency to maximize the liquid ligament length is experimentally observed. Such length simply cannot be obtained by other means under the same operating conditions, in the absence of the AC signal. At low frequency, we reach a transition from a well-behaved, uniform jet brought about near the optimum frequency to highly unstable liquid structures in which axisymmetry is lost rather abruptly
  • Miniatura
    Acceso AbiertoArtículo
    Controllable production of Janus ligaments by AC fields in a flow‑focusing junction
    (Springer, 2019-01) Castro Hernández, Elena De; García Sánchez, Pablo; León Rodríguez, Marta; Fernández Rivas, David; Ramos Reyes, Antonio; Universidad de Sevilla. Departamento de Ingeniería Aeroespacial y Mecánica de Fluidos; Universidad de Sevilla. Departamento de Electrónica y Electromagnetismo; Ministerio de Economía y Competitividad (MINECO). España
    We report the production of bicomponent Janus filaments of miscible aqueous fluids in a microfluidic electro-flow-focusing device under the action of an AC electric field. The production of liquid filaments can lead to the generation of microfibers by adding a subsequent process of polymerization. Janus microfibers are of paramount importance in biomedical applications such as tissue production on crimped scaffolds. We show that the filament length is a function of the frequency signal, voltage amplitude and of the viscosity and conductivity of the dispersed phase. In particular, Janus filaments with diameters ∼ 10 μm and longer than 1 mm are produced by AC voltages with frequencies below 150 kHz and a viscosity of the dispersed phase ∼ 10 cP.
  • Miniatura
    Acceso AbiertoArtículo
    Droplet group production in an AC electro- flow focusing microdevice
    (Springer, 2017-09) Castro Hernández, Elena De; García Sánchez, Pablo; Velencoso Gómez, Alfonso; Silas Jurado, Antonio; Fernández Rivas, David; Ramos Reyes, Antonio; Universidad de Sevilla. Departamento de Ingeniería Aeroespacial y Mecánica de Fluidos; Universidad de Sevilla. Departamento de Electrónica y Electromagnetismo; Ministerio de Economía y Competitividad (MINECO). España; Junta de Andalucía
    We report the production of droplet groups with a controlled number of drops in a microfluidic electro-flow focusing device under the action of an AC electric field. This regime appears for moderate voltages (500-700 V peak-to-peak) and signal frequencies between 25 and 100 Hz, much smaller than the droplet production rate ( ≈500 Hz). For this experimental conditions the production frequency of a droplet package is twice the signal frequency. Since the continuous phase flow in the microchannel is a Hagen-Poiseuille flow, the smaller droplets of a group move faster than the bigger ones leading to droplet clustering downstream.