Droplet group production in an AC electro-flow-focusing microdevice

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.Ministerio de Economía y Competitividad DPI2013-46485-C3-1-RMinisterio de Economía y Competitividad FIS2014-54539- PJunta de Andalucía P11-FQM-791

Stability of a rivulet flowing in a microchannel

publisher: Elsevier articletitle: Stability of a rivulet flowing in a microchannel journaltitle: International Journal of Multiphase Flow articlelink: http://dx.doi.org/10.1016/j.ijmultiphaseflow.2014.10.012 content_type: article copyright: Copyright © 2014 Elsevier Ltd. All rights reserved.publisher: Elsevier articletitle: Stability of a rivulet flowing in a microchannel journaltitle: International Journal of Multiphase Flow articlelink: http://dx.doi.org/10.1016/j.ijmultiphaseflow.2014.10.012 content_type: article copyright: Copyright © 2014 Elsevier Ltd. All rights reserved.publisher: Elsevier articletitle: Stability of a rivulet flowing in a microchannel journaltitle: International Journal of Multiphase Flow articlelink: http://dx.doi.org/10.1016/j.ijmultiphaseflow.2014.10.012 content_type: article copyright: Copyright © 2014 Elsevier Ltd. All rights reserved.publisher: Elsevier articletitle: Stability of a rivulet flowing in a microchannel journaltitle: International Journal of Multiphase Flow articlelink: http://dx.doi.org/10.1016/j.ijmultiphaseflow.2014.10.012 content_type: article copyright: Copyright © 2014 Elsevier Ltd. All rights reserved

Isothermal dissolution of small rising bubbles in a low viscosity liquid

publisher: Elsevier articletitle: Isothermal dissolution of small rising bubbles in a low viscosity liquid journaltitle: Chemical Engineering and Processing: Process Intensification articlelink: http://dx.doi.org/10.1016/j.cep.2014.08.002 content_type: article copyright: Copyright © 2014 Elsevier B.V. All rights reserved.publisher: Elsevier articletitle: Isothermal dissolution of small rising bubbles in a low viscosity liquid journaltitle: Chemical Engineering and Processing: Process Intensification articlelink: http://dx.doi.org/10.1016/j.cep.2014.08.002 content_type: article copyright: Copyright © 2014 Elsevier B.V. All rights reserved.publisher: Elsevier articletitle: Isothermal dissolution of small rising bubbles in a low viscosity liquid journaltitle: Chemical Engineering and Processing: Process Intensification articlelink: http://dx.doi.org/10.1016/j.cep.2014.08.002 content_type: article copyright: Copyright © 2014 Elsevier B.V. All rights reserved.publisher: Elsevier articletitle: Isothermal dissolution of small rising bubbles in a low viscosity liquid journaltitle: Chemical Engineering and Processing: Process Intensification articlelink: http://dx.doi.org/10.1016/j.cep.2014.08.002 content_type: article copyright: Copyright © 2014 Elsevier B.V. All rights reserved

Controlled cavity collapse: scaling laws of drop formation

The formation of transient cavities at liquid interfaces occurs in an immense variety of natural processes, among which the bursting of surface bubbles and the impact of a drop on a liquid pool are salient. The collapse of a surface liquid cavity is a well documented natural process that leads to the ejection of a thin and fast jet. Droplets generated through this process can be one order of magnitude smaller than the cavity's aperture, and they are consequently of interest in drop on demand inkjet applications. In this work, the controlled formation and collapse of a liquid cavity is analyzed, and the conditions for minimizing the resulting size and number of ejected drops are determined. The experimental and numerical models are simple and consist of a liquid reservoir, a nozzle plate with the discharge orifice, and a moving piston actuated by single half-sine-shaped pull-mode pulses. The size of the jetted droplet is described by a physical model resulting in a scaling law that is numerically and experimentally validated

Effect of a Surrounding Liquid Environment on the Electrical Disruption of Pendant Droplets

The effect of a surrounding, dielectric, liquid environment on the dynamics of a suddenly electrified liquid drop is investigated both numerically and experimentally. The onset of stability of the droplet is naturally dictated by a threshold value of the applied electric field. While below that threshold the droplet retains its integrity, reaching to a new equilibrium state through damped oscillations (subcritical regime), above it electrical disruption takes place (supercritical regime). In contrast to the oscillation regime, the dynamics of the electric droplet disruption in the supercritical regime reveals a variety of modes. Depending on the operating parameters and fluid properties, a drop in the supercritical regime may result in the well-known tip streaming mode (with and without whipping instability), in droplet splitting (splitting mode), or in the development of a steep shoulder at the elongating front of the droplet that expands radially in a sort of “splashing” (splashing mode). In both splitting and splashing modes, the sizes of the progeny droplets, generated after the breakup of the mother droplet, are comparable to that of the mother droplet. Furthermore, the development in the emission process of the shoulder leading to the <i>splashing</i> mode is described as a parametrical bifurcation, and the parameter governing that bifurcation has been identified. Physical analysis confirms the unexpected experimental finding that the viscosity of the dynamically active environment is absent in the governing parameter. However, the appearance of the <i>splitting</i> mode is determined by the viscosity of the outer environment, when that viscosity overcomes a certain large value. These facts point to the highly nonlinear character of the drop fission process as a function of the droplet volume, inner and outer liquid viscosities, and applied electric field. These observations may have direct implications in systems where precise control of the droplet size is critical, such as in analytical chemistry and “drop-on-demand” processes driven by electric fields