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Proceedings ArticleDOI

Vibration of water droplet located on a hydrophobic sheet under the tangential AC field

03 Oct 1999-Vol. 3, pp 1825-1830
TL;DR: In this paper, the behavior of a water droplet placed on the surface of the hydrophobic polymer sheet under AC field was investigated experimentally, and the amplitude of vibration strongly depends on the frequency and the volume of the droplet.
Abstract: The behavior of a water droplet placed on the surface of the hydrophobic polymer sheet under AC field was investigated experimentally. In order to confirm the effect of hydrophobicity on the movement of the water droplet, two kinds of hydrophobic insulating materials, PTFE and silicone rubber (SR) were used. A single water droplet was placed on the insulating sheet where AC electric field was applied. The frequency of AC voltage was varied from 10 to 100 Hz. The change of the droplet shape during vibration was investigated in detail. The droplet was deformed and synchronized with the AC field. The amplitude of vibration strongly depends on the frequency and the volume of water droplet. It was revealed that water droplet vibrates strongly at a definite frequency and the resonance frequency of a droplet with a volume of 10 /spl mu/l and 30 /spl mu/l is 30 Hz and 22 Hz, respectively.
Citations
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Journal ArticleDOI
TL;DR: In this article, the authors report the advances in the state of the art considering the relationships between the properties of functional surfaces, their applications and the technologies to engineer surfaces, and their applications in many advanced fields, such as: electronics, information technology, energy, optics, tribology, biology and biomimetics.

593 citations

Journal ArticleDOI
TL;DR: In this paper, the authors consider discharges between water drops when a limited alternating current is available, as experienced by an ageing insulator in service, and identify a phenomenon in which the length of a discharge between two drops is reduced through a particular type of distortion of the drops.
Abstract: Discharges between water drops are important in the ageing of hydrophobic outdoor insulators. They may also be important in the processes leading up to flashover of these insulators in high pollution conditions. This paper considers discharges between drops when a limited alternating current is available, as experienced by an ageing insulator in service. A phenomenon is identified in which the length of a discharge between two drops is reduced through a particular type of distortion of the drops. This is visually characterized as a liquid protrusion from each of a pair of water drops along the insulator surface. This process is distinct from vibration of the drops, general distortion of their shape and the very fast emission of jet streams seen in very high fields. The process depends upon the discharge current, the resistivity of the moisture and the hydrophobicity of the insulation surface.

47 citations


Cites background or result from "Vibration of water droplet located ..."

  • ...1 Impact of hydrophobicity Table 1 shows that PTFE and SiR have almost the same angle of contact with the water drops and are consistent with those reported elsewhere [11]....

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  • ...That the drops vibrate and distort in an ac field is also well established [10-13]....

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Journal ArticleDOI
T. Yamada1, Toshiyuki Sugimoto1, Yoshio Higashiyama1, M. Takeishi1, T. Aoki1 
30 Sep 2001
TL;DR: In this article, a single water droplet with a volume from 3 to 30 µ/l was placed between parallel electrodes which formed a uniform electric field in the tangential direction along the surface of a hydrophobic sheet.
Abstract: Resonance vibration of a water droplet located on the surface of a hydrophobic sheet under an AC electric field was investigated experimentally. In order to confirm the effect of the surface property of hydrophobic material on the resonance phenomena of a water droplet, three kinds of hydrophobic materials-silicone rubber (SR), polytetrafluoroethylene (PTFE) and polydimethylsiloxane-grafted fluoropolymer (PGF) sheet-were used. A single water droplet with a volume from 3 to 30 /spl mu/l was placed between parallel electrodes which formed a uniform electric field in the tangential direction along the surface of the hydrophobic sheet. A water droplet under an AC field vibrates strongly only at a particular frequency range. The resonance frequency where the water droplet vibrates strongly decreases with increasing the volume of the water droplet. The resonance frequency on the SR sheet is lower than that on the PTFE and the PGF sheet. The resonance frequency and the magnitude of the deformation of the water droplet depend on the surface properties of the hydrophobic material.

32 citations


Cites background from "Vibration of water droplet located ..."

  • ...The resonance frequency of the water droplet on the SR and the PTFE sheet under an ac electric field depends on the volume of the water droplet [ 14 ]....

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  • ...However, the droplet can deform or vibrate only at a definite frequency [ 14 ]....

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Journal ArticleDOI
TL;DR: The relationship between the size of water droplets on the surface of ac high-voltage conductors, their vibration, and corona onset is investigated in this paper, where the phase shift between the field and droplet vibration results in the maximum field occurring when the droplet is in a "flattened" profile rather than when it is pointeded.
Abstract: The relationship between the size of water droplets on the surface of ac high-voltage conductors, their vibration, and corona onset is investigated. Measurements have been carried out on individual droplets in high-voltage experiments, including high-speed photography, and discharge inception measurements. These have been correlated with acoustic emission from larger arrays of droplets on overhead transmission line conductors. A numerical model based on the finite element method has also been developed to simulate the vibration of the droplet enabling evaluation of the electric field and the characteristics of the droplet vibration. It is shown that the size of the water droplet is critical in its mechanical response to the field and that corona does not necessarily occur when the droplet is deformed into its most conical state as is the case under dc fields. For larger droplets the phase shift between the field and droplet vibration results in the maximum field occurring when the droplet is in a “flattened” profile rather than when it is “pointed.” The phase relationship between the droplet vibration and the electric field thus controls the onset of corona. It is argued that conductors which facilitate the development of small, uniform, stable droplets on their surface are the cause of abnormally high levels of low-frequency audible noise sometimes observed by transmission utilities. Moreover, the narrow resonant response of the droplet may lead to a difference in acoustic emissions experienced between power utilities with 50 and 60 Hz system frequencies.

16 citations

Proceedings ArticleDOI
10 Jun 2012
TL;DR: In this article, the authors investigated the dynamic behavior of water droplets subject to AC electric fields by experiment and finite element modeling. But the authors focused on the phase shift between vibration and exciting voltage in a single droplet and the evolution of electric field within the whole cycle of vibration.
Abstract: The dynamic behaviour of water droplets subject to AC electric fields is investigated by experiment and finite element modelling. The motion of a water droplet is considered on the surface of a metallic sphere. To understand the consequences of vibration, the FEA model is introduced to study the dynamics of a single droplet in terms of phase shift between vibration and exciting voltage. Moreover, the evolution of electric field within the whole cycle of vibration is investigated. The finite element treatment to couple the electromagnetic field with multi-phase flow field is described. The profile of the electric field and the characteristics of mechanical vibration are evaluated. Surprisingly the phase shift in these characteristics results in the maximum field occurring when the droplet is in a flattened profile rather than when it is ‘pointed’.

14 citations


Cites background from "Vibration of water droplet located ..."

  • ...LITERATURE REVIEW A number of papers can be found employing high speed cameras as an effective technique to observe the electrohydrodynamic behavior of droplets [6-8]....

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References
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Journal ArticleDOI
TL;DR: In this article, it was shown that a conical interface between two fluids can exist in equilibrium in an electric field, but only when the cone has a semi-vertical angle 49.3$^\circ$.
Abstract: The disintegration of drops in strong electric fields is believed to play an important part in the formation of thunderstorms, at least in those parts of them where no ice crystals are present. Zeleny showed experimentally that disintegration begins as a hydrodynamical instability, but his ideas about the mechanics of the situation rest on the implicit assumption that instability occurs when the internal pressure is the same as that outside the drop. It is shown that this assumption is false and that instability of an elongated drop would not occur unless a pressure difference existed. When this error is corrected it is found that a drop, elongated by an electric field, becomes unstable when its length is 1.9 times its equatorial diameter, and the calculated critical electric field agrees with laboratory experiments to within 1%. When the drop becomes unstable the ends develop obtuse-angled conical points from which axial jets are projected but the stability calculations give no indication of the mechanics of this process. It is shown theoretically that a conical interface between two fluids can exist in equilibrium in an electric field, but only when the cone has a semi-vertical angle 49.3$^\circ$. Apparatus was constructed for producing the necessary field, and photographs show that conical oil/water interfaces and soap films can be produced at the caloulated voltage and that their semi-vertical angles are very close to 49.3$^\circ$. The photographs give an indication of how the axial jets are produced but no complete analytical description of the process is attempted.

2,994 citations

Journal ArticleDOI
TL;DR: In this paper, the authors investigated the flashover mechanism of silicone rubber composite insulators and found that it is attributed to the hydrophobicity of the silicone rubber and the diffusion of low molecular weight (LMW) polymer chains.
Abstract: Experimental results show that the contamination performance of silicone rubber composite insulators is better than porcelain insulators. This is attributed to the hydrophobicity of the silicone rubber. This suggests that the flashover mechanism of these insulators is different. This paper experimentally investigates contamination build-up, diffusion of low molecular weight (LMW) polymer chains, surface wetting, electrical field caused interaction between droplets, generation of conductive regions and filaments, field intensification caused spot discharge and the ultimate flashover of silicone rubber along wetted filaments. The studies resulted in a new flashover mechanism, which provides a better understanding of the superior performance of silicone rubber outdoor insulators. The results will be useful for the development of improved laboratory test procedures and to evaluate composite insulators' performance in contaminated conditions. The part of the paper describes an overview of the flashover mechanism and the diffusion of LMW polymer chains and wetting of the silicone rubber surface in detail. >

138 citations

Proceedings ArticleDOI
01 Jan 1997
TL;DR: In this article, the influence of water-droplets at the surface of HV-insulators on the distribution of the electrical field was investigated and correlations between the characteristics of the droplets such as their distance and shape, the insulating surface conditions (stage of hydrophobicity) and the electrical stress parameters such as the electric field between the droplet, the local field strength and the correlated forces.
Abstract: This paper deals with the influence of water-droplets at the surface of HV-insulators on the distribution of the electrical field. As compared with the electrostatic field under dry conditions an essential local field enhancement may occur and may trigger low energy micro surface discharges. These discharges are supposed to be a main source of early surface ageing. Little is known about the basic phenomena in the so-called "early" stage of ageing. Investigations were carried out by using model insulators with a-more or less-homogenous droplet layer at the surface. Experiments showed correlations between the characteristics of the droplets such as their distance and shape, the insulating surface conditions (stage of hydrophobicity) and the electrical stress parameters such as the electric field between the droplets, the local field strength and the correlated forces. Factors responsible for the actual shape of a droplet are the relevant electrical field strength and the stage of surface hydrophobicity. Until now only few systematical investigations determining the influence of the field distribution between single droplets are known or published. This paper presents a contribution to this fundamental problem and shows the advantage of applying careful numeric simulations as well as experimental studies.

24 citations

Proceedings ArticleDOI
12 Oct 1998
TL;DR: In this paper, the behavior of water droplets placed on the surface of a hydrophobic polymer plate under a DC field was investigated experimentally, where three kinds of hydrophilic insulating materials-PTFE, silicone rubber, and ethylene propylene rubber (EPDM)-were used.
Abstract: The behavior of water droplets placed on the surface of a hydrophobic polymer plate under a DC field was investigated experimentally. In order to confirm the effect of hydrophobicity on the movement of the water droplet, three kinds of hydrophobic insulating materials-PTFE, silicone rubber (SR) and ethylene propylene rubber (EPDM)-were used. Water droplets were placed on the insulating plate in contact with the aluminum foil electrode or placed between the thin foil electrodes. A single droplet placed in contact with the electrode on the SR or EPDM plate was elongated and a water filament extended along the surface by the electrostatic force, while that on the PTFE plate left the electrode. The water droplet placed on the border of electrode at the PTFE plate was deformed and formed a semi-cone at a triple junction. The apparent contact angle varied with time for a constant applied voltage and some amounts of charge were emitted by micro discharge or by ejection of small droplets. The behavior of the droplets under DC field strongly depends on not only the hydrophobicity but also the surface property of an insulating plate.

20 citations

01 Jan 1998
TL;DR: In this paper, the behavior of water droplets placed on the surface of the hydrophobic polymer plate under de field was investigated experimentally, where three different materials PTPE, silicone rubber (SR), and ethylene propylene rubber (EPDM) were used.
Abstract: The behavior of water droplets placed on the surface of the hydrophobic polymer plate under de field was investigated experimentally. In order to confirm the effect of hydrophobicity on the movement of the water droplet, three kind of hydrophobic insulating materials PTPE, silicone rubber (SR), and ethylene propylene rubber (EPDM) were used. Water droplets were placed on the insulating plate in contact with the aluminum foil electrode or placed between the thin foil electrodes. A single droplet placed in contact with the electrode on the SR or EPDM plate was elongated and a water filament extended along the surface by the electrostatic force, while that on the PTFE plate left the electrode. The water droplet placed on the border of electrode at the PTFE plate was deformed and formed a semi-cone at a triple junction. The apparent contact angle varied with time for a constant applied voltage and some amounts of charge were emitted by micro discharge or by ejection of small droplets. The behavior of the droplets under dc field strongly depends on not only the hydrophobicity but also the surface property of an insulating plate.

18 citations