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Localized electrical discharges have been used to generate vapor bubbles in dielectric liquids, and the growth and collapse of these bubbles has been recorded photographically. The optical studies are based on a flash-illuminated shadowgraph apparatus. The expansion and collapse of a cavity in the low viscosity limit follows a simple hydrodynamic model and the predictions of the model are experimentally...
The effect of moisture on the inception of partial discharges (PD) along a liquid-solid dielectric interface was investigated in an arrangement incorporating a solid dielectric plate between the flat end-faces of two coaxial cylindrical electrodes immersed in transformer oil or hexadecane. PD parameters were evaluated by measurements of light pulses with a sensitive photomultiplier as well as by an...
The simultaneous recordings of the transient currents and optical events following a rectangular wave voltage has been taken to do a systematic study of prebreakdown phenomena in dielectric liquids. A very simple optical method using a laser beam and a photodiode is used to measure the steamer velocity. Negative streamers produce a series of current pulses, while positive one produce only a single...
This study has allowed us to appreciate quantitatively the processes governing the injection law in polar liquids at high fields and to distinguish the wide variety of intricate phenomena at low fields. The fundamental role of the double layer is emphasized, especially how the compact part and/or the diffuse part of this layer control the current flow according to the amplitude of the field. Several...
We have studied the transient currents flowing in silicone oils subjected to voltage steps with polarity reversal. The experiments have been carried out, at room temperature, on two 50 cSt viscosity polydimethylsiloxane silicone oils (Rhône-Poulenc 604 V 50 and Dow Corning 561) in a parallel plate conductivity cell as a function of the applied electric field strength (0.4 ≦ E(kV.cm−1) ≦ 10), of the...
Trichlorotrifluoroethane (C2Cl3F3) is a stable molecule up to a temperature of 700°C. Under internal arc stress C2Cl3F3 was decomposed and Phosgene and other products were produced. The amount of produced Phosgene depends on the fed in energy per unit of gas mass and the presence of Oxygen. At the ignition of an arc in liquid C2Cl3F3 a shock-wave with amplitudes of up to 1 MPa occurs dependent on...
Transient DC-conductivity measurements of anthracene solutions in cyclohexane have provided evidence for solvent ionization following irradiation with 248nm excimer laser pulses. A mechanism resulting in a cyclohexane cation and an anthracene anion as near neighbors can explain the experimental observations: a high mobility species, 7–8 absorbed photons per solute molecule, intensity dependence, and...
A computer model of the field enhanced motion of impurity particles has been developed by some of the authors. It requires as input data some parameters, relevant essentially to the contact phase, in which the charge exchange between particle and electrode takes place. To make easy the parameter identification, an advanced data acquisition system, allowing an automatic analysis of film frames obtained...
Dielectrophoresis of particles in liquid media has been well studied under the assumption of ideal dielectrics. Real dielectrics exhibit non-zero conductivity, however, and this fact brings about behaviours unpredictable by the model of ideal dielectrics. In the present work some attempts to experimentally investigate the dielectrophoretic motion of a lossy dielectric sphere suspended in a liquid...
Photoconductivity induced by 347 nm light pulses in TMPD solution in liquid methylcyclohexane is measured. The unusual current kinetics has been found at T < 200 K when the light pulse duration was less or about the time taken for separation of initial electron-ion pairs. The kinetics is associated with the current of geminate electrons and has been shown to be consistent with predictions of the...
A possible model for the primary stage of nasal olfaction can be developed around the possibility of far infrared electro-magnetic detection. To explore this possibility the dispersive dielectric properties of the system are required. The dielectric behaviour of glycoprotein gells which make up the main environment in this situation are reported. There is some evidence reported for the presence of...
Low frequency dielectric measurements (5 Hz–100 MHz) in parallel with Differential Scanning Calorimetry were used to study the behavior of a water-in-dodecane microemulsion as a function of increasing water content, C-mass fraction, in the interval 0.024≤C≤0.4, upon decreasing temperature from 20°C down to −190°C. The presence of “free” and “interfacial” water molecules was evidenced and a differentiation...
The dielectric, conductivity and ultrasonic measurements for p-azoxy anisole are done in its solution in benzene and carbon tetrachloride at room temperature. The dipole moment and relaxation time are computed using a new alternative method as suggested by Johri(1984) and compared with Gopala Krishna microwave method, Higasi and Guggenheim statical methods. Adiabatic compressibility, Rao number, Vanderwaals...
The diffuse part of the electric double layer spontaneously present at an insulator/liquid interface can be displaced by an A.C. field. It is shown that the diffuse part of the double layer acts as a reservoir of ions which gives rise to a time-limited unipolar injection. At low fields, tanδ increases when the voltage V is increased. At high fields, the reservoir of charges depletes quickly and the...
In this paper the temperature dependence of the static and the high frequency permittivities of some saturated fatty acids of the series CnH2nO2 in the liquid phase are reported. From such data information on the associating behaviour and on the structure of the liquids are deduced in the light of the Kirkwood-Fröhlich theory for polar fluids. A discussion is then made on the dependence of association...
Several properties such as the density, viscosity, dielectric constant and electric strength of n-alkanes have been discussed with respect to the number of C-atoms (N) in the molecule. The linear dependence of these properties on N shows some kind of deviation around N=9 which has been qualitatively discussed. The dependence of electric strength on liquid viscosity is also discussed.
This paper reports the results of experimental investigations on the breakdown phenomenon of transformer oil under inhomogeneous field conditions (rod-plate electrode system) and subjected to DC voltage superimposed on AC voltage. The peak breakdown voltage of transformer oil is found to be decrease with the increasing of ripple content in the applied voltage and gap spacing between electrodes. It...
The most commonly used types of uniform field electrodes for dielectric strength tests in dielectric liquids are briefly recalled and analyzed, and the most significant criteria for the design of electrodes for the above purpose are reviewed and discussed. A new kind of uniform field electrodes which seems to suit better than the usual ones the above criteria is then presented; besides, the procedure...
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