AC electrified jets in a flow-focusing device: Jet length scaling

Elena Castro-Hernández (1) , Pablo García-Sánchez (2) , Javier Alzaga-Gimeno (1) , Say Hwa Tan (3) , Jean-Christophe Baret (4) , Antonio Ramos (2)

1 Area de Mecanica de Fluidos, Departamento de Ingenieria Aeroespacial y Mecanica de Fluidos
2 Departamento de Electrónica y Electromagnetismo [Universidad de Sevilla]
3 Queensland Micro and Nano Technology Centre
4 CRPP - Centre de recherches Paul Pascal

We use a microfluidic flow-focusing device with integrated electrodes for controlling the production of water-in-oil drops. In a previous work, we reported that very long jets can be formed upon application of AC fields. We now study in detail the appearance of the long jets as a function of the electrical parameters, i.e., water conductivity, signal frequency, and voltage amplitude. For intermediate frequencies, we find a threshold voltage above which the jet length rapidly increases. Interestingly, this abrupt transition vanishes for high frequencies of the signal and the jet length grows smoothly with voltage. For frequencies below a threshold value, we previously reported a transition from a well-behaved uniform jet to highly unstable liquid structures in which axisymmetry is lost rather abruptly. These liquid filaments eventually break into droplets of different sizes. In this work, we characterize this transition with a diagram as a function of voltage and liquid conductivity. The electrical response of the long jets was studied via a distributed element circuit model. The model allows us to estimate the electric potential at the tip of the jet revealing that, for any combination of the electrical parameters, the breakup of the jet occurs at a critical value of this potential. We show that this voltage is around 550 V for our device geometry and choice of flow rates.

Mots clés: Electric fields; Convection currents; Electrodes; Fluid jets; Fluid drops

Domaines: Matière Condensée [cond-mat]

Elena Castro-Hernández, Pablo García-Sánchez, Javier Alzaga-Gimeno, Say Hwa Tan, Jean-Christophe Baret, et al.. AC electrified jets in a flow-focusing device: Jet length scaling. Biomicrofluidics, 2016, 10 (043504), pp. 1-11. ⟨10.1063/1.4954194⟩. ⟨hal-01344266⟩