Liquid dielectric

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

Study of the vegetal oil as a substitute for mineral oils in distribution transformer

Abstract: There are so many factors that negatively affect distribution transformer operations, especially its electrical insulation system. Traditionally mineral oil has been used as insulating material, however, in the last years there is a growing interest in using vegetable oil, these fluids are currently being used in the range of small to medium distribution power transformers. The purpose of this work is to determine distribution transformer performance using natural ester dielectric fluid compared to those with standard mineral oil. The most significant factor that affects insulation material deterioration is temperature increments due to overload. We used the ASTM standard test method for analysis of gases dissolved in electrical insulating oil, to assess the aging of transformer insulation paper in natural ester dielectric fluid compared to that in conventional transformer oil. The results showed that distribution transformers using vegetable oil has a useful life longer than others using mineral oil, roughly 42,86 percent.

Convective heat transfer through polarized dielectric liquids

Abstract: An electrically insulating layer of a dielectric liquid confined between horizontal conducting electrodes, the upper of which is warmer, becomes unstable with respect to the onset of steady convection when the voltage between the plates reaches a critical value. In a rapidly varying ac field this instability is due to the Kelvin body force which depends on the polarization P and the gradient of the electric field E. Our recent linear stability analysis [Chem. Phys. Letters 179, 311 (1991)] for the critical voltage showed that as the gravitational Rayleigh number becomes increasingly negative the critical wave number at the onset of convection becomes very large. We now extend this analysis to examine how the Nusselt number depends on the extent of supercriticality in the weakly nonlinear regime. As the temperature drop between the plates increases the fraction of the heat transfer associated with convection is found to pass through a maximum value when the critical horizontal wave number is close to 4 times its value when gravity is absent.

Effect of finite conductivity on the nonlinear behaviour of an electrically charged viscoelastic liquid jet

Abstract: In this paper a one-dimensional numerical study on the nonlinear behaviour of an electrically charged jet of Oldroyd-B viscoelastic, Taylor–Melcher leaky dielectric liquid is carried out. The effect of surface charge level, axial wavenumber and finite conductivity on the nonlinear evolution of the jet is investigated. Different structures including beads-on-a-string with/without satellite droplets, quasi-spikes and spikes are detected, and their domains in the plane of the non-dimensional axial wavenumber and the electrical Bond number are illustrated. The underlying mechanisms in the formation of the structures are examined. It is found that tangential electrostatic force plays a key role in the formation of a quasi-spike structure. Decreasing liquid conductivity may lead to a decrease in the size of satellite droplets or even the complete removal of them from a beads-on-a-string structure, induce the transition from a beads-on-a-string to a quasi-spike structure or postpone the appearance of a spike. On the other hand, finite conductivity has little influence on filament thinning in a beads-on-a-string structure, owing to the fact that the electrostatic forces are of secondary importance compared with the capillary force. The difference between the finite conductivity, large conductivity and other cases is elucidated. An experiment is carried out to observe spike structures.

Measurement of the Interfacial Tension in an Ionic Liquid–Dielectric Liquid System Using an Electrically Deformed Droplet

Abstract: The unique chemical and physical properties of ionic liquids (ILs) are attracting an increasing amount of interest in energy and biological fields. However, some physicochemical properties of ILs are not well-known. Here, we present an alternative method for the measurement of the interfacial tension in an IL–dielectric liquid system by means of the small deformation of a charged IL droplet in a dielectric medium. Using the pendant drop method, the validity of the proposed measurement method is confirmed. The interfacial tension between ILs and silicone oil has been found to be lower than that between water and silicone oil, and the tension is negatively correlated to the size of the IL ion. Further analyses of Girifalco-Good’s interaction parameters of the two liquid–liquid systems demonstrate that the lower interfacial tension of IL can be attributed to the stronger intermolecular interaction between IL and silicone oil molecules. Due to a universal feature of the interaction parameter for a given class...

Nonlinear oscillations of gas bubbles submerged in water: implications for plasma breakdown

Abstract: Gas bubbles submerged in a dielectric liquid and driven by an electric field can undergo dramatic changes in both shape and volume. In certain cases, this deformation can enhance the distribution of the applied field inside the bubble as well as decrease the internal gas pressure. Both effects will tend to facilitate plasma formation in the gas volume. A practical realization of these two effects could have a broad impact on the viability of liquid plasma technologies, which tend to suffer from high voltage requirements. In this experiment, bubbles of diameter 0.4?0.7?mm are suspended in the node of a 26.4?kHz underwater acoustic standing wave and excited into nonlinear shape oscillations using ac electric fields with amplitudes of 5?15?kV?cm?1. Oscillations of the deformed bubble are photographed with a high-speed camera operating at 5130?frames?s?1 and the resulting images are decomposed into their axisymmetric spherical harmonic modes, , using an edge detection algorithm. Overall, the bubble motion is dominated by the first three even modes l?=?0, 2 and 4. Electrostatic simulations of the deformed bubble's internal electric field indicate that the applied field is enhanced by as much as a factor of 2.3 above the nominal applied field. Further simulation of both the pure l?=?2 and l?=?4 modes predicts that with additional deformation, the field enhancement factors could reach as much as 10?50.