Electrohydrodynamical Research Articles

Water film motor driven by alternating electric fields: Its dynamical characteristics

The "liquid film motor," a novel device with important implications for basic research and technology, is analyzed. It works perfectly with both direct current (dc) and alternating current (ac) fields. We develop a mathematical model describing electrohydrodynamical (EHD) motions induced by ac fields, which are more complex and have wider technological applications than those produced by dc fields. The main characteristics of these motions, derived in our paper and in full agreement with the experimental ones, are as follows: (i) Rotation of the film requires that the frequencies of the ac fields are exactly the same and their magnitudes surpass a threshold, which depends on their phase difference. (ii) Vibrations may be induced by fields with different frequencies. (iii) The EHD motions strongly depend on the polarization induced by the external electric field. However, these motions are little affected by the liquid's electrical conductivity, viscosity, dielectric constant, and density. Our model also predicts several features, which have yet to be experimentally verified.

Properties of liquid jet induced by electrohydrodynamic pumping in dielectric liquids

AbstractLiquid‐jet phenomena induced by electrohydrodynamical (EHD) pumping were investigated in isothermal dielectric liquids without direct charge injection at a metal/liquid interface. A pseudo‐doughnut to plane electrode system was used to generate an EHD liquid jet, and the liquid jet properties were measured using four different dielectric liquids (which are referred to as DBDN, BCRA, Tr‐Oil, and FS‐Oil in this paper). The maximum velocity and pumping pressure achieved were 1.5 m/s and 5.5 kPa, respectively, at an applied voltage of 23 kV with approximately 2.5 W of electrical power consumption in BCRA. It is considered that this liquid jet is due to pure conduction pumping. This mechanism is associated with heterocharge layers near the electrodes which are based on the process of dissociation and recombination of the electrolytic species. Furthermore, to obtain high directivity of the liquid jet, two special nozzles (herein referred to as a normal nozzle and spiral nozzle) were designed. A highly directed liquid jet was obtained using the spiral nozzle. In this case, the flow pattern was of a spiral structure. It is considered that this spiral jet is produced by both the Coanda effect and the nozzle shape (conical hole). © 2002 Scripta Technica, Electr Eng Jpn, 138(4): 1–9, 2002; DOI 10.1002/eej.1132

垂直方向送液用電気流体力学ポンプの安定動作条件

垂直方向送液用電気流体力学ポンプの安定動作条件

液体誘電体中のEHDポンピングによる液体ジェットの特性

Liquid-jet phenomena induced by electrohydrodynamical (EHD) pumping were investigated in isothermal dielectric liquids without direct charge injection at a metal/liquid interface. A pseudo-doughnut to plane electrode system was used to generate an EHD liquid jet, and the liquid jet properties were measured using four different dielectric liquids (which are referred to as DBDN, BCRA, Tr-Oil, and FS-Oil in this paper). The maximum velocity and pumping pressure achieved were 1.5 m/s and 5.5 kPa, respectively, at an applied voltage of 23 kV with approximately 2.5 W of electrical power consumption in BCRA. It is considered that this liquid jet is due to pure conduction pumping. This mechanism is associated with heterocharge layers near the electrodes which are based on the process of dissociation and recombination of the electrolytic species. Furthermore, to obtain high directivity of the liquid jet, two special nozzles (herein referred to as a normal nozzle and spiral nozzle) were designed. A highly directed liquid jet was obtained using the spiral nozzle. In this case, the flow pattern was of a spiral structure. It is considered that this spiral jet is produced by both the Coanda effect and the nozzle shape (conical hole). © 2002 Scripta Technica, Electr Eng Jpn, 138(4): 1–9, 2002; DOI 10.1002/eej.1132

Interrelation between configuration of electrodes for induction electric charging and collector current wind EHD power generator

This work aims to realize a wind electrohydro- dynamical (EHD) power generator using induction electric charging with a water jet. The electrodes for induction electric charging are composed of an orifice of which inner radius is 1.5mm and a ring made of a copper wire of which diameter is 1.5mm. It is important to design the electrodes that maximize induction electric charge. In this paper, it is experimentaly clarified that the ring electrode of inner diameter of 3.7cm gives the collector short current of the wind EHD power generator more than that of 4.7cm but has dispersion of the collector short current more than that of 4.7 cm.

High‐Rate Copper Dissolution in Hydrochloric Acid Solution

The dissolution of copper in 1 M chloride solution was studied by steady‐state (current‐potential curves for various disk rotation rates) and transient measurements [frequency analysis of the electrochemical and electrohydrodynamical (EHD) impedance]. The anodic polarization curves present four regions according to the potential: one region of mixed kinetics followed by another of mass‐transport control characterized by one plateau, followed by a second mixed kinetics region and a second plateau. The results obtained for the first domain of mixed kinetics and for the first plateau were previously published. In this work, the second mixed kinetics region is considered. From the analysis of the ac and EHD impedance measurements, it was shown that a transition between the presence and the absence of a CuCl salt layer occurs at a critical potential. The value of this critical potential depends on the rotation rate; the higher the rotation rate, the higher the potential value. A model of kinetic dissolution for this transition is presented, and a coupling between the currents corresponding to the two reactions is demonstrated.

Electrohydrodynamical(EHD) Research of Saturated Pool Boiling Heat Transfer.

The enhancement of the saturated pool boiling heat transfer utilizing electric field has been studied. By selecting a small-scale heat transfer surface of 5 mm in diameter, the nucleate boiling heat transfer without the enhancement effect of the movement of boiling bubbles along the heat transfer surface has been realized to quantitatively examine the bubble deformation effect of the applied electric field. The boiling curves which have been experimentally obtained showed the enhancement ratio to be about twice that in the case where no electric field is applied. Therefore, by comparing these data with our previously obtained nucleate boiling curves on the larger heat transfer surface of 50 mm in diameter, which showed the enhancement ratio of about 50 times, it has been clarified that the effect of the deformation of bubbles in the electric field making the larger bottom area would cause the enhancement ratio of about twice and that the effects of violent motion of the bubbles along the surface would cause the additional increase of the enhancement ratio. To measure the thickness of the liquid film on the heat transfer surface under the boiling bubble, a capacitance probe has been devised by use of a heterodyne detector. Based on the results obtained using this capacitance proble, the high wall superheat increases the time of dissipation of liquid film in the case without the applied electric field. However, the liquid film on the heat transfer surface does not dissipate in high wall superheat due to continuous supply of liquid with applied electric field.

Effect of pH on the mediated oxidation of [Fe(CN) 6] 4− at polyaniline film electrodes. An impedance study

The [Fe(CN) 6] 4− oxidation at polyaniline (PANI) modified electrodes was studied by electrohydrodynamical (EHD) and a.c. impedances at moderate acid concentrations (pH range 2–3). Experimental diagrams were obtained for different values of pH, potential, [Fe(CN) 6] 4− concentration, electrode rotation rate and film thickness and compared with a kinetic model developed by taking into account PANI acid-base equilibria. This model accounts for low frequency relaxation observed by both impedance techniques and explains in a semiquantitative way the influence of the experimental parameters.

Corrosion inhibition of pure iron in neutral solutions by electrochemical techniques

Steady-state current-voltage curves for various disk rotation rates were combined with transient measurements (frequency analysis of the electrochemical and electrohydrodynamical impedance) in order to investigate the corrosion inhibition by an organic surfactant of pure iron in an aerated 0.5 M NaCl solution. In the cathodic range, physical adsorption of the compound with the interfacial potential was observed leading to the thickening or strengthening of the film. Thus, for short times of polarization, due to the adsorption relaxation, it was necessary to compensate the ohmic drop in the circuit to obtain the electrohydrodynamical (EHD) curves. The inhibitor acts by forming a porous layer covering the surface. From the analysis of the EHD diagrams the thickness and the porosity of the film were estimated. Nevertheless, a non-classical behaviour in the HF range of the EHD diagrams was observed and interpreted by a mechanical action of the fluctuating flow on the film. At the corrosion potential, the electrochemical impedance diagrams were essentially representative of the charge transfer process. Diffusion across the inhibitor film is very slow and requires extremely low modulation frequencies (below 1 mHz).

Mass‐Transport Study for the Electrodissolution of Copper in 1M Hydrochloric Acid Solution by Impedance

The dissolution of copper in 1M chloride solution was studied by steady‐state (current‐voltage curves for various disk rotation rates) and transient [frequency analysis of the electrochemical and electrohydrodynamical (EHD) impedance] measurements. The anodic polarization curves have presented one region of mixed kinetic and another of mass‐transport control characterized by a current plateau. The limiting current is a function throughout the whole range of rotation rates. From the EHD impedance diagrams observed below the anodic plateau, it was shown that the limitation by mass transport is due to . On the current plateau, the presence of two time constants on the EHD impedance diagram and the reductibility of the curves have been attributed to the existence of a salt layer covering the surface, the rate of formation of this layer being identical to the rate of dissolution. A layer model has been developed.

The influence of electric fields on the intensity of rectification

The rectification of binary mixtures of ethanol-water and acetone-water was studied for the case of static, alternating and pulsed electric fields. It was found out that as electric discharge occured in a gas region the increase of mass transfer could be mainly due to electric wind turbulizing of the vapour phase. In this case the intensity of rectification mass transfer was to 1.7 times higher than under free condition. For the first time the rectification in the regime of electrohydrodynamical (EHD) spraying of liquids was investigated. To do this, the conditions of atomization by an electric field of conductive liquids with high surface tension are determined and realized in the rectifying column. The regime of EHD spraying of liquid was the most efficient one for the rectification in imposed electric fields. The mechanism of electric fields effects on mass transfer and the role of process parameters in these effects are discussed in detail. The new methods and equipment for the realization of mass transfer processes in gas-liquid systems were developed and investigated. It was shown that the EHD mass transfer apparatus has better diffusive and hydrodynamic characteristics compared with packed, pipe and cascade tray fractionating columns.

Heat Transfer Characteristics of an EHD Condenser. (Second Report. the Development of an EHD Condenser).

The effect of electrohydrodynamical (EHD) phenomena on the enhancement of condensation heat transfer has been researched to develop the high performance heat pump. The actual proof test of EHD condenser has been performed for the condenser of high temperature heat pump (temperature of about 150°C) by utilizing the heat transferring medium of C6F14 (perflorohexan) and the influence of the lubricating oil on the performance of EHD condenser (shell-tube condenser) of 50kW capacity which was composed of 102 vertical tube) has also been researched experimentally. Enhancement ratio of condensation heat transfer has been attained up to 6 times by using C6F14 and we clarified that the lubricating oil has not negative effects on this EHD condenser.

Experimental study of EHD pseudo-dropwise condensation.

In order to realize the higher performance heat pump, an electro-hydrodynamical (EHD) condenser utilizing the combination of two kinds of EHD phenomena has been researched. In this study, to maximize the augmentation effect, experimental study has been carried out to clarify the details of an EHD pseudo-dropwise condensation. The diameter of the drops has decreased according to the increase of the electric field. The condensation heat transfer coefficients have increased in proportion to the electric field strength to realize the maximum local heat transfer coefficients of over 9000 W/m2K in CFC 113 and over 11000 W/m2K in HCFC 123. Furthermore, the heat transfer coefficients have become of the same order under the condition of the the same quantity of falling condensate.

An ac and electrohydrodynamical (EHD) impedance investigation of redox processes occurring at polyaniline-coated electrodes

The redox processes of the [Fe(CN) 6] 3− 4− couple mediated by polyaniline films were studied by steady-state, ac and EHD impedance methods. At pH < 1, charging and discharging of the polymer capacitance in parallel with the faradaic impedance of the substrate reaction, occurring at the polymer-electrolyte interface, are the processes which determine the transient behaviour. Neither the charge transport across the film nor the charge-transfer kinetics of either the substrate or the polymer are experimentally accessible. At less acidic pHs (~ 3), a low frequency phenomenon detected in EHD experiments seems to be associated with surface protonation equilibria.

The theory of ac and EHD impedances for a mediated reaction on a redox polymer modified electrode

The ac and electrohydrodynamical (EHD) impedances have been calculated for an electrode modified by a redox polymer in contact with a solution containing a redox couple. The expressions obtained are functions of the diffusion coefficient of electrons in the film, the redox capacitance of the polymer film and its thickness, and the faradaic impedances on both sides of the film. These impedances, established for a rotating disc electrode by considering quantitatively convective diffusion effects, were simulated to illustrate the relative contribution of each process.

Augmentation of convective and boiling heat transfer by applying an electro-hydrodynamical liquid jet

The augmentation effects of an electro-hydrodynamical (EHD) liquid jet on convective and boiling heat transfer were experimentally and theoretically analyzed. The EHD liquid jet, which was the jet flow ejected through the ring electrode in the direction away from the plate, was produced by applying a high electric voltage between the ring electrode and the plate electrode. The convective heat transfer from the plate electrode was enhanced over 100 times by the forced convection and the turbulent effects of the EHD liquid jet. For the boiling heat transfer, the mean bubble detachment period was decreased, and the critical heat flux was enhanced over two times.

Transient Mass Transfer at a Coated Rotating Disk Electrode: Diffusion and Electrohydrodynamical Impedances

The mass‐transfer response of a rotating disk electrode to a sine wave modulation of the angular velocity has been calculated for an interface covered by a porous layer of thickness , through which an ionic species is transported by molecular diffusion with a diffusivity . Electrohydrodynamical (EHD) impedances, defined as the transfer functions between the response of the concentration or concentration gradient at the interface and the modulated velocity, have been expressed as functions of a dimensionless frequency p, representing the ratio of the modulation frequency to the average angular velocity, of the permeability and of the diffusion time constant through the film . The frequency analysis of the impedance data for a coated electrode, therefore, allows one to determine and separately.

EHD study of the corona wind between wire and plate electrodes

The corona wind, with a velocity of several meters per second, is caused by applying high electric tension to bring about corona discharge in gases. In this paper the corona wind is experimentally and theoretically analyzed from an electrohydrod ynamical (EHD) standpoint. Experiments have been performed mainly in nitrogen by a two-dimensional electrode arrangement of a fine wire anode and a plate cathode. The voltage-current characteristics of an electrostatic probe indicate that positive ions predominate in the whole space except in an extremely narrow region close to the wire. A theoretical analysis has been conducted based on the model that positive ions produced by ionization near the wire electrode move toward the plate, introducing the bulk convective motion of neutral molecules as the result of collisions of ions and neutral molecules. The electric potential distribution in the space and pressure distribution on the plate calculated numerically agree well with the experimental data. Consequently, it is made clear that the corona wind is caused by the Coulomb force exerted on ions and collisions of ions and neutral molecules of gas.