Search

Conductivity and ionization mechanisms in liquid helium have been investigated by using high field conduction phenomena occurring near a sharp needle electrode. When the voltage Vs, applied between the needle and the plane is greater than some threshold voltage Vs, a corona-like discharge regime was observed. Charge carriers are generated in the high field region close to the point where an intense light emission is detected. Above Vs the mean current is space charge limited and the mobility of charge carriers has been deduced from analysis of current-voltage characteristics. Some parameters of the corona-like region have been deduced from a spectral analysis of the light emitted during the discharge. [ABSTRACT FROM AUTHOR]

The present paper is mainly devoted to phenomena occurring in point-plane electrode geometry, where breakdown is the result of the initiation and propagation of prebreakdown phenomena called "streamers". In this configuration, an investigative study of the streamer initiation processes, requiring very high electric field strengths (~ MV/cm), and of propagation (requiring low electric field, ~ kV/cm) can easily be carried out for negative streamer development as well as for the positive case. From analysis of experimental results in pure liquids the physical processes connected with streamer initiation and propagation, particularly the electronic ones, are presented and discussed. Estimations of the main parameters of slower subsonic streamers and of the faster filamentary ones (such as field strength at the streamer tip, field inside the channel, charge density, etc.) have been obtained from qualitative considerations and compared to experimental data. [ABSTRACT FROM AUTHOR]

Two electrically insulating fuels of mineral and biological origins have been tested for electrostatic charging in single and multiple blade-plane configurations. The aim is to investigate methods to dramatically increase the total injected current, with a view to developing an atomization system where the charge injection and atomization units are separate. In this study, the fuel is quiescent and only the injected current is measured. Current flux - electrode surface electric field (J-E) characteristics at different bladeelectrode gaps are presented. A current density of 6.5 A/m2 is obtained at a surface electric field of 100 MV/m using the 1-blade configuration. From the measured data, the relation between the blade-electrode gap (d) and the injected current flux is found as Jα d-m at constant voltage, where m is found to be 2 for flat charge collectors and as high as 4 for rounded collectors. The physics of the swirl motion caused by the Coulomb forces are discussed. The size of this induced flow is correlated to the performance of the multiple blade design. Charge injection, dielectric liquids, electrostatic charging, induced flow, multi-blade injector [ABSTRACT FROM AUTHOR]

A charge injection atomizer functions by introducing electric charge discharged from a high voltage electrode into a dielectric liquid, which subsequently atomizes the ejected liquid jet. Atomizer evolution thus far has proceeded through trial and error analysis of the experimentally measured electrical characteristics of the atomizer and of the quality of atomization. Within the atomizer, a coupled space charge and electric field exist, which can alter the internal flow pattern, thus creating electrohydrodynamic (EHD) instabilities that affect atomizer operation. Such a system has not been simulated in the past under forced flow conditions. In this work we simulate the internal flow of such a charge injection device in two dimensions; using experimental based boundary conditions. Initial results indicate that in the linear injection regime defined by the experimental data, the flow is only slightly unstable but in the transitional and highly non-linear regimes, the coupled space charge and electric field produce more instability in the liquid that must be investigated further. [ABSTRACT FROM AUTHOR]