Dielectric Soil Research Articles

Natural convection heat transfer from discrete heat sources mounted in rectangular enclosure surrounded by a single-phase liquid coolant (Dept.M)

In the present work, natural convection heat transfer from discrete heat sources mounted in rectangular enclosure using liquid coolant is investigated. Heat transfer from discrete heaters is non-uniform and should be accounted for by applying the averaging techniques. The averaged two-dimensional governing equations along with the standard k-e model and wall function are solved using the SIMPLE algorithm. The effects of the e cooling fluid type water and dielectrics oil, the different heat flux and time on heat transfer are investigated. The results are compared with experimental measurements. Results show that water gives a good cooling effect compared with dielectrics oil. Maximum heat transfer occurs at the heater leading and side edges. The heater surface temperature is highest at the top-row heaters. Results show also good agreement between the theoretical and experimental measurements.

LASER-EXCITED VOLUME SECONDARY RADIATION IN WIDE-GAP SEMICONDUCTORS AND DIELECTRICS

Studies of the volume secondary radiation (photoluminescence and Raman scattering) in wide-gap semiconductors (GaP, ZnSe) and condensed dielectrics were carried out at various temperatures. The low-temperature variations of the dielectric constants were evaluated. The anti-Stokes photoluminescence from the sample bulk, resulting from interband and impurity recombination, was observed for the first time when exciting the spectra of secondary radiation by the continuous radiation of a low-power helium--neon laser with the lasing line in the transparency region of gallium phosphide. A similar effect was observed at low temperatures in zinc selenide excited by an argon laser. Photoluminescence from the sample bulk was also found for a number of condensed dielectrics (hydrocarbons and oil) at room temperature. The results obtained allow analysis of impurities in the bulk of semiconductors and dielectrics based on recording the volume photoluminescence spectra.

Influence of electrode geometry on ion-drag pump static pressure

A research program aimed at developing an EHD pump for insulating liquids is in progress at the Electrical Engineering Department of the University of Genova. The initial part of this program considered a single stage ion drag pump and was aimed at the optimization of the relevant electrodes (materials and geometry) and interelectrode gap to obtain a high hydrostatic pressure. The experimental data on three different technical grade liquid dielectrics (oils) are reported. They allow a comparison with two different theoretical pressure vs. voltage relations, due to Stuetzer and to Pickard, for each tested liquid. The general validity of such relations is discussed and questioned. The latter point and the experimental data here reported illustrate that, at present, it is necessary to introduce, early in the design process of this kind of EHD pumps, an experimental stage, specific to each liquid to be used.