Waermetransport durch freie Konvektion in grossen Reaktoren fuer Fluessigkeitssysteme mit inneren, homogen verteilten Waermequellen Abschlussbericht

SIGLEAvailable from TIB Hannover: F95B1377+a / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekBundesministerium fuer Forschung und Technologie (BMFT), Bonn (Germany)DEGerman

Modeling and characteristics comparison of two different piezoelectric transformers

Electromagnetic transformers have become obstacles to progress power supply miniaturization. Thus, piezoelectric transformers, which are more compact, immune to magnetic field and that present a high galvanic insulation, become more and more an alternative to electromagnetic transformers. In this paper, two different piezoelectric transformers have been studied and compared: a Rosen type and a radial mode type. The first approach consists in performing an analytical model. This approach is inspired by the technique used in electroacoustics and allows to build an electric equivalent circuit of the vibrating structure. The second approach deals with numerical finite element method using ANSYS software. A three-dimensional finite element model of each transformer has been then simulated to find out the resonance frequency but also to determine the transformation ratio as a function of the frequency for several values of the load resistance. In order to validate the models, experiments have been performed. Measurements of the voltage gain, output power and efficiency of both piezoelectric transformer types have been obtained and compared taking into account their characteristics

The Sensitivity of Thermohaline Groundwater Circulation to Flow and Transport Parameters: A Numerical Study Based on Double-Diffusive Convection above a Salt Dome

This article explores double-diffusive convective fluid motion in an aquifer above a salt dome. Aside from the ambient regional flow regime, the hydraulic conditions in an aquifer connected with a salt formation are determined by differences in salinity. Whereas density-driven flow patterns induced by the effect of salt have been studied before we focus on the additional effect of temperature. For the model setup, we select typical parameter values that are characteristic of not only the lowlands in Germany and Poland. For the computation of flow in a vertical cross-section, we use numerical modeling with COMSOL Multiphysics. The size and strength of eddies in the high salinity region above the aquifer base are strongly influenced by thermal effects. A sensitivity study shows a wide range of convection phenomena, ranging from the absence of convective motions via steady and oscillating circulation to unsteady fluctuating patterns. The flow and transport parameters show the highest sensitivity to the thermal Rayleigh number

Simulation of Deep Geothermal Heat Production

Abstract: Geothermal heat production from deep reservoirs (5000-7000 m) is currently examined within the collaborative research program "Geothermal Energy and HighPerformance Drilling" (gebo), funded by the Ministry of Science and Culture of Lower Saxony (Germany) and Baker Hughes. The projects concern exploration and characterization of geothermal reservoirs as well as production. They are gathered in the four major topic fields: geosystem, drilling, materials, and technical system. We present modelling of a reference set-up concerning the geothermal production itself