Liquid dielectric

About: Liquid dielectric is a research topic. Over the lifetime, 3702 publications have been published within this topic receiving 45150 citations.

Simple theoretical estimation of the dielectric strength of gases

Abstract: Understanding how a gas is able to strongly insulate electric devices is certainly of great importance to the electrical engineering community. More precisely, modeling how a dielectric gas stops an electric current requires to understand what makes a gas a good dielectric, or in other words, what makes a gas presenting a high dielectric strength (DS). We show how to easily estimate the DS of a gas by calculating its ability to absorb light.

Positive discharge development in insulating oil: optical observation and simulation

Abstract: Results of optical investigations of positive discharge channel development in transformer oil under divergent field configuration and impulse voltages to 650 kV are presented. The propagation of two different discharge structures (bush-like, tree-like) and the transition between these structures were observed. The conditions of their development and boundary of the bush-to-tree transition were determined. Anomalous behavior of the breakdown time dependence on applied voltage, consisting of a sharp drop in time at a critical voltage, was found. The dielectric breakdown model modified by introducing the varying channel conduction is presented. In the model discharge channel propagation is described by stochastic development of current and field instabilities. The model describes adequately the main spatial and temporal features of the various discharge structures observed in the experiments. The current and field characteristics of the simulated discharge channels which belong to different structures are compared. The bush-to-tree transition and the anomalous dependence of the breakdown time on voltage were explained by current instability in bush-structure channels.

Nonlinear EHD stability of the interfacial waves of two superposed dielectric fluids

Abstract: The slow modulation of the interfacial capillary–gravity waves of two superposed dielectric fluids with uniform depths and solid horizontal boundaries, under the influence of a normal electric field and in the absence of surface charges at their interface, is investigated by using the multiple-time scales method. It is found that the complex amplitude of quasi-monochromatic traveling waves can be described by a nonlinear Schrodinger equation in a frame of reference moving with the group velocity. The stability characteristics of a uniform wave train are examined analytically and numerically on the basis of the nonlinear Schrodinger equation, and some limiting cases are recovered. Three cases appear, depending on whether the depth of the lower fluid is equal to, greater than, or less than the depth of the upper fluid. The effect of the normal electric field is determined for the three stability regions of the pure hydrodynamic case. It is found that the normal electric field has a destabilizing influence in the first stability region and a stabilizing effect in the second and third stability regions. Moreover, one new unstable region or two new stable and unstable regions appear, all of which increase when the electric field increases. On the other hand, the complex amplitude of quasi-monochromatic standing waves near the cutoff wavenumber is governed by a similar type of nonlinear Schrodinger equation in which the roles of time and space are interchanged. This equation makes it possible to estimate the nonlinear effect on the cutoff wavenumber.

Electric field induced sheeting and breakup of dielectric liquid jets

Abstract: We report experimental observations of the controlled deformation of a dielectric liquid jet subjected to a local high-voltage electrostatic field in the direction normal to the jet. The jet deforms to the shape of an elliptic cylinder upon application of a normal electrostatic field. As the applied electric field strength is increased, the elliptic cylindrical jet deforms permanently into a flat sheet, and eventually breaks-up into droplets. We interpret this observation—the stretch of the jet is in the normal direction to the applied electric field—qualitatively using the Taylor-Melcher leaky dielectric theory, and develop a simple scaling model that predicts the critical electric field strength for the jet-to-sheet transition. Our model shows a good agreement with experimental results, and has a form that is consistent with the classical drop deformation criterion in the Taylor-Melcher theory. Finally, we statistically analyze the resultant droplets from sheet breakup, and find that increasing the applied electric field strength improves droplet uniformity and reduces droplet size.

Effect of Thermal Modulation on the Onset of Electrothermoconvection in a Dielectric Fluid Saturated Porous Medium

Abstract: An electroconvection in a horizontal dielectric fluid saturated with a densely packed porous layer is investigated under the simultaneous action of vertical electric field and vertical temperature gradient when the walls of the layer are subjected to time periodic temperature modulation. The dielectric constant is assumed to be a linear function of temperature. A regular perturbation method based on small amplitude of applied temperature field is used to compute the critical values of Rayleigh number and wave number. The shift in the critical Rayleigh number is calculated as a function of frequency of modulation, electric Rayleigh number, Prandtl number, and Darcy number, and their effects on the critical Rayleigh number are discussed. The situations which are favorable for the design of artificial organs without the side effect of hemolysis are explained. Copyright © 2009 by ASME.