Liquid dielectric

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

Thermal and mechanical numerical modelling of electric discharge machining process

Abstract: In electric discharge machining (EDM), the heat gradients caused by the electric discharge create a non-uniform local thermal expansion on the level of the surface layers of machined materials from where genesis of thermal stresses takes place. These thermal stresses, if exceeding yield stress, can remain and become residual after the cooling of the part. The modelling of these phenomena, during the heating by the electric discharge and the cooling by the dielectric liquid, requires a heat transfer model, the material behaviour identification, a thermo-mechanical model for the thermal and the residual stress models. This paper presents numerical results concerning the temperature distribution, the thermal and residual stresses of a stable steel material (AISI316L) machined by EDM. Comparison of numerical results with experimental data and numerical results from the literature shows good agreement and is hence quite satisfactory. Copyright © 2008 John Wiley & Sons, Ltd.

Initiation from a point anode in a dielectric liquid

Abstract: For original paper see Kim and Hebner, ibid., vol.13, p.1254 (2006). In this discussion, the initiation of a positive streamer from the tip-electrode when a high voltage is applied to a tip-plane measurement cell filled with cyclohexane is discussed. The authors suggest that the initiating process is the formation of electron avalanches near the positive tip. In the present case the high field is concentrated around the tip anode. Fermi level of the metal electrode is energetically located in the middle of the forbidden gap of cyclohexane, electrons from molecules adsorbed at the surface of the tip and of adjacent layers can tunnel into the metal giving rise to the injection of positive charges. This process is called field ionization and has been invoked in the explanation of injection currents in liquids. In liquid cyclohexane strong incoherent scattering prevents the formation of a Rydberg state. Mean free path for electrons in cyclohexane changes by about three orders of magnitude between a thermal energy situation and one in which there is energy available to electrons due to electric fields with magnitudes like those under the conditions studied. So, our postulate was based on consideration of the dynamic properties rather than the equilibrium properties. The discussion of the model stating that the experimental results were consistent with such a model, and ended by characterizing the model as a framework in which experimental results can be reconciled. Kim and Hebner reply to the comments.

Numerical Study of Electroconvection in a Dielectric Layer Between Two Cofocal Elliptical Cylinders Subjected to Unipolar Injection

Abstract: The problem of electroconvection in an annular space between two elliptical concentric cylinders filled with a dielectric liquid and subjected to internal unipolar injection is considered. A finite volume method is used to solve the governing equations, including the Navier–Stokes ones and a simplified set of the Maxwell equations. For the first time the whole set of these coupled equations is solved, using the elliptical-cylindrical coordinates. We first validate numerical simulation in this field by comparing the results obtained with those available in the literature. The numerical solution of the electroconvection problem is then followed by a detailed analysis of the flow structure and electric charge distribution. It is shown that the multicellular convective pattern is observed. It is noticed that unipolar charge injection from the internal electrode significantly changes the topology of the fluid flow. Finally, the influence of various system parameters, such as the injection level and electric Rayleigh number, is also investigated.

Liquid cooled ozone generator

Abstract: An ozone generator module of the electirc discharge field type is provided having at least one cell comprising an assembly of three concentric tubular members, the inner and outer tubular members being electrodes separated by a tubular dielectric member spaced from one of the electrodes a distance sufficient to define a high density electric discharge zone between them, the cell or cells being disposed within a liquid container. Substantially optimum conditions for the production of ozone are provided by making the cross sectional dimension of the field uniform throughout to within a very small range of tolerance and by controlling the temperature of the electrodes by cooling them with liquid coolants one of which is a dielectric liquid, and limiting the density of the field by regulating the voltage across the field and the frequency employed.

DC-field in solid dielectric cables under transient thermal conditions

Abstract: The electric field in a dielectric changes from capacitive grading immediately after the voltage application to, resistive grading under steady state conditions. In the case of a polymeric dielectric, the conductivity is known to be strongly dependent on both the electric field and the temperature, characterized by an activation energy in the range of 0.5 to 1.2 eV. The dielectric constant /spl epsi//sub 0//spl middot//spl epsi//sub r/ for an olefinic polymer is almost independent of the applied field and temperature, in contrast to the electrical conductivity /spl sigma/, which has a strong dependence on both temperature and field, in the parameter range of engineering interest for a DC cable. During normal operating conditions, load current will heat the conductor and generate a temperature gradient across the dielectric. This temperature gradient will change the electric field distribution in a resistively graded dielectric, with a time constant determined by field- and temperature-dependent carrier mobility, which controls the evolution of space charge towards a steady state condition characterized locally by the dielectric time constant.