Liquid dielectric

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

Application of pulsed HV discharges to material fragmentation and recycling

Abstract: The physical basis of electric impulse fragmentation and its applications to the recycling of composite materials are reviewed. The method is based on the initiation of a pulsed electric discharge inside the solid dielectric material. With pulse amplitudes of /spl sim/300 kV, material layers of /spl sim/2 cm can be punctured. Specific energy deposition, of /spl lsim/100 J/cm at a GW power level, leads to pressure buildup of /spl lsim/10/sup 10/ Pa in the discharge channel. Pressure waves and radially propagating cracks are launched into the solid body, which can lead to the separation of inclusions from the matrix or to detachment at material boundaries. To induce the discharge in the solid dielectric it must be immersed in a dielectric liquid with higher breakdown strength. Most applications use water, which has excellent breakdown strength at fast ramp rates and, due to its high permittivity, leads to field concentration in the solid dielectric. Electric impulse fragmentation is a clean physical method without any environmental burden and therefore well suited for recycling applications. In this paper we consider applications in the fields of demolition debris, incineration ashes, contaminated surface layers, electric appliances, glass, and elastoplastic materials. Finally, the economy and the scaling of the technique to large material throughput are discussed.

Electrohydrodynamically induced dielectric liquid flow through pure conduction in point/plane geometry

Abstract: Mildly polar liquids generally exhibit an ohmic behavior when subjected to electric fields of limited values. The resulting conduction is then associated with heterocharge layers of finite thickness in the vicinity of the electrodes. In the absence of charge injection or induction, a simple conduction model based on the processes of dissociation of a neutral electrolytic species and recombination of the generated ions is presented. This model is first applied to parallel plane electrode geometry to describe the build-up of the heterocharge. Then, the case of point/plane configuration is considered where the effect of Coulomb force is different in the two layers next to the electrodes. A net motion toward the point electrode is predicted to occur. With a rough approximation for the harmonic field, an analysis is presented which leads to an expression for the axial component of the net force exerted on the liquid. A simple static pump is designed and built to experimentally investigate the pressure head generated through pure conduction. Two working fluids (refrigerant R-123 and n-hexane) and two different electrode designs are considered in this study. The experimental results are qualitatively compared to the theoretical predictions.

The electrohydrodynamic deformation of drops suspended in liquids in steady and oscillatory electric fields

Abstract: When an electric field is applied to a drop suspended in another liquid the drop deforms. The relation between the applied field and the mode and magnitude of the deformation have been studied extensively. Nevertheless, Torza, Cox & Mason (1971) found that quantitative agreement between the leaky dielectric theory (Taylor 1966) and experiment is quite poor. Here we describe results from a new series of experiments. Drops suspended in weakly conducting liquids were deformed into spheroids with both steady and oscillatory fields. Drop deformation, interfacial tension, and the electrical properties of the fluids were measured for each system to provide a definitive test of the theory. The agreement between the leaky dielectric model and our results for drop deformations in steady fields is much improved over previous results, although discrepancies remain for some systems. Drop deformations in oscillatory fields consist of steady and oscillatory parts because of the quadratic dependence on the field strength. Measurements of the steady part at 60 Hz, where the oscillatory deformation is negligible, are in excellent agreement with the theory. The effects of frequency on the steady deformation were studied by measuring oblate deformations at a series of frequencies and field strengths; the agreement with theory is good. Finally, the time-dependent total deformation was measured under conditions where both parts of the deformation are commensurate. Good agreement was found between the measured and predicted maximum and minimum deformations. Nevertheless, only a small range of fluid properties could be studied owing to the need to avoid droplet sedimentation.

Progress in the Field of Electric Breakdown in Dielectric Liquids

Abstract: For some fifty years the mechanism of electric breakdown in liquid insulation has been a subject of great interest for both theoretical as well as practical reasons. Over the years a number of promising hypotheses of breakdown have been advanced and it has been necessary to modify, and sometimes reject, interpretations of the breakdown data as additional experimental evidence has been accumulated.