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Session Chair: Christophe LOUSTE, P' institute University of Poitiers, France Session Chair: Pedro A Vazquez, Universidad de Sevilla, Spain
ID: 1200 / S2: 1
PIV flow measurements of conduction pumping flow created by nine pairs of asymmetric surface electrodes
Christophe Louste1, Philippe Traore1, Pedro Vasquez2, Jamal Seyed Yagoobi3
1P' institute University of Poitiers, France; 2Dpt. Fisica Aplicada III E.T.S.I., Unversidad de Sevilla; 3Department of Mechanical Engineering Worcester Polytechnic Institute
In this paper, the electrohydrodynamic flow generated by nine electrode pairs of asymmetric electrodes is experimentally investigated. Electrodes are flushed into a cavity wall and a DC voltage is applied to the electrodes in order to set the liquid in motion. The liquid flow patterns are recorded by the use of a particles velocity Image system. Flows have been recorded during more than 500s and time variations are presented. According to the theory the flow over each electrode pair is most of the time directed from to small electrode to the large one but unpredicted flow patterns have also been obtained. It can be noticed that an unexpected reversed flow has even been observed in some configurations. In order to explain these behaviors, a joint analysis of both flow patterns and measured electric current is made. This last point is more particularly discussed in the last part.
ID: 1133 / S2: 2
A Non-destructive Thermal Stimulus Method as a Tool for studying the Electrical Double Layer
Xavier Sidambarompoulé1, Jean Charles Laurentie1, Petru Notingher1, Thierry Paillat2, Paul Leblanc2, Alain Toureille1, Gérard Touchard2, Olivier Guille1
1IES, Université de Montpellier, CNRS, MONTPELLIER, FRANCE; 2Institut Pprime, CNRS - Université de Poitiers - ISAE-ENSMA, POITIERS, FRANCE
When a liquid is put into contact with a solid, two charge layers of opposite signs appear at the interface. This Electrical Double Layer (EDL) is the result of electrochemical reactions occurring in the region separating the liquid and the solid. A bottleneck in understanding and quantifying the EDL and its behavior is the availability of direct methods allowing to fully measure the EDL charge and distribution. This paper concerns the use of the Thermal Step Method (TSM) as a tool for characterizing the EDL to complete the flow electrification method. Several dielectric liquids (cyclohexane, mineral oil and silicon oil) are subjected to thermal step measurements. The obtained results are analyzed and discussed with respect to literature and to numerical simulations.
ID: 1344 / S2: 3
Mapping the thickness of falling liquid films under ionic wind by a light absorption technique
DESTEC, University of Pisa, Italy
The paper shows the development of a photometric technique for mapping the thickness of liquid films, subject to corona wind. The phenomenon of light absorption through a layer of dyed liquid is used to evaluate its thickness. The layer receives a back-illumination from the wetted wall and the transmitted intensity of light is measured by means of a digital camera. Non-uniformities in the original intensity field suggest building a calibration curve for each measurement point. The filtering and interpolation algorithm needed for transforming the intensity field into the thickness field is described in detail. In addition to being non-intrusive and inexpensive, the technique can determine the local film thickness with an accuracy lower than 10 % of its measuring range amplitude. Application to mapping the thickness of falling liquid films under ionic wind in different regimes and at different waviness is illustrated. It is particularly interesting to study this phenomenon, since an ionic wind, with electrical currents lower than 1 mA, can create additional waves and ripples on the liquid/gas interface, thus, in practical applications, it increases mass and heat transfer between the two phases with a negligible energy expense. Falling film thickness is measured with and without the generation of corona wind by a thin wire. The pattern of surface ripples can be observed over the entire illuminated area and the beneficial effect on surface waviness can be evaluated at both polarities of the applied high voltage.
ID: 1118 / S2: 4
Conditions for explosive growth of free surface perturbations for a dielectric liquid in a normal electric field in confined axisymmetric geometry
Konstantin Bobrov1, Nikolay Zubarev1,2, Olga Zubareva1
1Institute of Electrophysics, UB RAS, Russian Federation; 2Lebedev Physical Institute, RAS, Russian Federation
We consider the behavior of the free surface of an ideal dielectric liquid in an applied normal electric field for the case of confined axisymmetric geometry of the system. The quadratic nonlinear amplitude equation which describes the evolution of the boundary is derived in the framework of the Hamiltonian formalism. According to this equation, the hard regime of excitation of electrohydrodynamic instability is always realized. Also, it is shown that the part of the potential energy functional which is responsible for the higher-order nonlinearities is negatively defined if the dielectric constant of the liquid is sufficiently large, 𝜀 > 2.78. Under this condition, the growth of surface perturbations has an explosive character.