44 research outputs found
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