Study of the transition from conduction to injection in an electrohydrodynamic flow in blade-plane geometry

A dielectric fluid can be set into motion with the help of electric forces, mainly Coulomb force. This phenomenon, called electroconvection, can be induced by electrohydrodynamic conduction, injection, and induction. Conduction is based on the dissociation/recombination phenomenon, generates heterocharge layers, and occurs for low electric field values. Injection produces homocharge layers in the electrode vicinity and requires stronger electric fields to be initiated. This study is an experimental observation of the transition from conduction to injection of a dielectric liquid in blade-plane geometry using Particle Image Velocimetry. In addition, the electric current is measured to completely understand the flow behavior

Properties of Fuel Spray Obtained by Electrohydrodynamic Atomization

[EN] Airblast atomization is commonly used to atomize fuel in aircraft engines. An annular liquid sheet is atomized by the shear forces exerted by the co-flowing air stream. Nevertheless, this technique is less effective in some specific cases, e.g. when the external air flow velocity is relatively low. Electrohydrodynamic (EHD) atomization can constitute a solution in these cases. It consists of applying an electric field between two electrodes and electrically charging the passing carburant. This phenomenon will create instabilities within the liquid, provoking therefore its atomization. The main objective is therefore to electrically atomize a liquid sheet without the application of an external air flow like in airblast atomizers. This paper presents a novel actuator, based on dielectric barrier injection, used to induce instabilities within a plane liquid sheet of fuel similar to the annular sheet in aircraft engines. The behaviour of this atomizer was described in previous works. Several modes were observed, sometimes leading to a complete atomization, or just inducing instabilities and oscillating the liquid sheet. In the present study, only the cases where the liquid sheet is completely atomized are investigated. Images were recorded with the help of a high speed camera. Primary atomization is only studied, secondary atomization being neglected. The properties of the spray obtained by EHD atomization are investigated thoroughly, namely the breakup length, the mesh size, the drople t diameter, the droplet count, etc.Daaboul, M.; Saba, N.; Rishmany, J.; Louste, C. (2017). Properties of Fuel Spray Obtained by Electrohydrodynamic Atomization. En Ilass Europe. 28th european conference on Liquid Atomization and Spray Systems. Editorial Universitat Politècnica de València. 480-487. https://doi.org/10.4995/ILASS2017.2017.5018OCS48048

Etude et développement d'actionneurs electrohydrodynamiques pour le contrôle des écoulements (application à l'atomisation des nappes liquides)

Ce travail porte sur le contrôle électrohydrodynamique (EHD) des écoulements et plus particulièrement sur la mise au point d'une méthode de visualisation ainsi que sur le développement d'actionneurs. Dans une première partie, une analyse bibliographique rappelle les principes fondamentaux de l'EHD. Dans le deuxième chapitre, la méthode de vélocimétrie par image de particules (PIV) est adaptée au cas des écoulements EHD. La validité des mesures PIV en présence d'un champ électrique est analysée sur un écoulement de référence : le panache chargé bidimensionnel. Ensuite, dans le troisième chapitre, deux actionneurs utilisant deux techniques différentes d'injection sont examinés. Le premier actionneur étudié est basé sur la configuration lame-plan. La comparaison du jet 2D plan obtenu avec différents écoulements classiques de la mécanique des fluides permet de souligner les particularités du système. Les résultats obtenus permettent d'envisager des applications dans l'industrie aérospatiale. Le second actionneur utilise l'injection à barrière diélectrique. L'étude du comportement à l'aide de la méthode PIV a montré que le flux induit se comporte principalement comme un jet de paroi. Dans le chapitre quatre, l'actionneur est ensuite placé dans un injecteur afin d'obtenir la pulvérisation d'une nappe de carburant. Les différents paramètres testés montrent l'efficacité de la méthode. En conclusion, les deux actionneurs EHD ont montré leurs capacités à agir sur un liquide. Cette technique a été appliquée avec succès à la pulvérisation d'une nappe de carburant. Elle est particulièrement intéressante en aéronautique dans le cas où un écoulement externe d'air ne peut être utilisé.This work is a study of the electrohydrodynamic (EHD) control of fluid flows, more particularly, an adaptation of a visualization method and the development of EHD actuators. In a first part, the general points of the EHD principles are presented. Then, the Particle Image Velocimetry (PIV) method is adapted on EHD flows. Its validity is discussed in the presence of an electric field and analyzed on a typical EHD flow: the two-dimensional charged plume. Afterwards, in the third part, two actuators using two different injection techniques are examined. The first actuator is based on the blade-plate geometry. The comparison of the generated 2D jet with classical fluid mechanics flows underlines the advantages of the system. The results obtained with this actuator allocate several applications in the aerospace industry. The second actuator uses the dielectric barrier injection. The study of its behavior with the PIV method has shown that the induced flow is similar to a wall jet. In the fourth chapter, an EHD actuator is embedded in a fuel injector in order to pulverize a liquid sheet. The tested parameters show the efficiency of this method. In conclusion, both EHD actuators have shown their ability to act on a liquid. This technique was applied on the atomization of a fuel liquid sheet. It is particularly interesting in aeronautics in the case where an external air flow cannot be applied.POITIERS-BU Sciences (861942102) / SudocSudocFranceF

Experimental Models of the Variation of HFE-7100 and HFE-7000 Electric Properties With Temperature

International audienceHFE-7000 and HFE-7100 have shown a promising importance in the electrohydrodynamic (EHD) domain. Their dielectric properties are investigated in a temperature range between -20 and 60 °C for relative permittivity and electric conductivity and between -20 and 80 °C for breakdown voltage. The aim is to electrically characterize these liquids and to develop experimental models to be used in numerical simulations. Mathematical models of electric properties are essential for understanding the physical phenomena that can affect the performance of EHD systems. The development of these models can then help design more reliable EHD devices and optimize their performance

Electroconvective Cavity Flow Patterns Created by Asymmetric Electrode Configuration

This paper is an experimental study on electroconvective flows produced by an asymmetric electric field in a cavity. It is part of a scientific project aiming to develop electrohydrodynamic (EHD) flow actuator in order to enhance heat transfer and mixing efficiency in fluidic and microfluidic systems. In this study, the EHD flow is obtained by applying a dc voltage between two electrodes (cylinder/plane) immersed in a working liquid. The produced velocity fields strongly depend on the applied voltage. Whatever may be the applied voltage, the fluid goes from the cylinder toward the plate or the other way round. The velocity fields obtained by particle image velocimetry for different potentials are analyzed in both cases with the usual mechanisms (injection and conduction) at the origin of the motion of the liquid. A discussion on the transition between injection and conduction phenomena is finally presented.Fil: Louste, Christophe. Université de Poitiers; FranciaFil: Romat, Hubert. Université de Poitiers; FranciaFil: Traore, Philippe. Université de Poitiers; FranciaFil: Daaboul, Michel. University of Balamand; LíbanoFil: Vazquez, Pedro. Universidad de Sevilla; EspañaFil: Sosa, Roberto. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad de Buenos Aires; Argentin

Study of the Dielectric Behavior of HFE-7000 in function of Electric Field and Temperature Variations

International audienceNowadays, heat transfer enhancement devices are becoming very essential in many applications. Most of electronic devices, from the simplest to the most sophisticated, contain processors. Advanced processors require efficient cooling for an optimal performance. Due to the growing interest in faster and lighter devices, researchers always seek to innovate and optimize cooling strategies. In spatial applications, the use of typical cooling systems can cause complications due to the vibrations during takeoff and due to zero gravity effects. Electrohydrodynamic (EHD) pumping, which is based on the interaction of a dielectric liquid with an electric field, could present a solution to all these challenges. EHD pumps were considered a breakthrough in the field of cooling since they demonstrate many advantages over other types of pumps. EHD devices are less power consuming, lighter and cheaper. They don't have moving parts and they are suitable for microgravity applications. The hydrofluoroethers (HFE) are dielectric liquids that could be ideally utilized in these pumps for many applications. Being dielectric fluids with eco-friendly properties, HFEs could replace CFCs, HFCs, HCFCs, and PFCs. Due to their promising EHD applications, studies must be done to investigate the variation of their dielectric behavior with electric field and with temperature. This work presents an experimental investigation of the dielectric characteristics of HFE-7000 with temperature variations. Understanding this aspect can help enhance and optimize the performance of EHD systems

Etiology of End-Stage Renal Disease and Arterial Stiffness among Hemodialysis Patients

Background:. Prior studies have demonstrated that conventional and emerging CV risk factors are associated with worsening arterial stiffness among end-stage renal disease (ESRD) patients on hemodialysis. The present cross-sectional study evaluates the association between the etiology of ESRD and arterial stiffness among a cohort of hemodialysis patients. Methods. Etiology of ESRD was identified from patients' medical records and classified as either vascular renal disease, diabetic nephropathy, nondiabetic glomerulopathy, tubular interstitial nephropathy, hereditary nephropathy, or ESRD of unconfirmed etiology. Results. A total of 82 subjects were enrolled. cfPWV was independently associated with the composite of either diabetic nephropathy or vascular renal disease (p = 0.022), pulse pressure (p = 0.001), and a history of CV events (p = 0.025), but not history of hypertension or diabetes mellitus alone. The median cfPWVs in diabetic nephropathy and vascular renal disease were comparable and significantly higher than median cfPWVs in other etiologies of ESRD. Conclusion. The study suggests that the etiology of ESRD is independently associated with arterial stiffness among hemodialysis patients. Furthermore, arterial stiffness was higher among patients who developed renal sequelae of either diabetes mellitus or hypertension as compared with those who have a history of either diabetes mellitus or hypertension alone