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Heat Conductivity (heat + conductivity)
Selected Abstracts3D Edge Transport Studies with EMC3-EIRENE for the Dynamic Ergodic Divertor (DED) at TEXTORCONTRIBUTIONS TO PLASMA PHYSICS, Issue 1-3 2008D. Harting Abstract In this paper we introduce some model extensions to the energy balances of the 3D fluid Monte-Carlo code EMC3 and study their influence on the simulation results for TEXTOR-DED. We implemented local kinetic corrections to the classical parallel heat conductivity of electrons (heat flux limit). Depending on the DED configuration, a cooling effect in the outermost SOL region, resulting from the heat flux limit, can be observed. In addition, also the adiabatic cooling term mnV2, which was neglected before, was implemented into the energy iterations. This term causes a localized cooling of the ions in front of the wall, where the plasma is accelerated towards the first wall. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Tomography of temperature gradient metamorphism of snow and associated changes in heat conductivityHYDROLOGICAL PROCESSES, Issue 18 2004Martin Schneebeli Abstract Temperature gradient metamorphism is one of the dominant processes changing the structure of natural dry snow. The structure of snow regulates the thermal and mechanical properties. Physical models and numerical simulations of the evolution of the snow cover require a thorough understanding of the interplay between structure and physical properties. The structure of snow and the heat conductivity were measured simultaneously without disturbance in a miniature snow breeder. The structure was measured by microtomography, and heat conductivity by measuring heat fluxes and temperatures. A temperature gradient from 25 to 100 K m,1 was applied to the snow. The snow density range of the samples varied from 150 to 500 kg m,3. The density in the observed volume remained constant during the experiments under temperature gradient conditions. The structure was analysed with respect to the size of typical ice structures and air pores, specific surface area, curvature and anisotropy of the ice matrix. The temporal changes in structure and heat conductivity are compared. The heat conductivity changed by as much as twice its initial value, caused by changes in structure and texture, but not due to changes in density. This shows the enormous importance of structure in the evolution of the heat conductivity. The observed changes are not in good agreement with the current understanding of the metamorphic process, because heat conductivity increased during temperature gradient metamorphism, instead of the expected decrease due to a shrinking of the bonds. We also observed a plateau in the evolution of the heat conductivity coefficient, which indicates a quasi-steady state of the structural evolution with respect to thermophysical properties of snow. Copyright © 2004 John Wiley & Sons, Ltd. [source] Homogenization technique for transient heat transfer in unidirectional compositesINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN BIOMEDICAL ENGINEERING, Issue 7 2003Marcin Kami Abstract The article presented is devoted to the homogenization of transient heat transfer problems in unidirectional composites. Mathematical model is based on the effective modules method applied to unidirectional periodic composites,the effective heat conductivity is calculated in the closed form; the effective volumetric heat capacity for the entire composite is obtained by simple spatial averaging. Such a homogenization scheme makes it possible to significantly simplify numerical analysis of transient heat phenomena in various types of unidirectional composites with complicated microgeometry. The comparison of transient heat transfer problem for the composite in real and homogenized configuration is carried out using a specially adopted finite element method computer program. Copyright © 2003 John Wiley & Sons, Ltd. [source] Nonwoven as heat barrier: Modeling of the efficiency of Carbtex fibersJOURNAL OF APPLIED POLYMER SCIENCE, Issue 5 2008Serge Bourbigot Abstract In this work, we examine the use of nonwoven (NW) as heat barrier to protect a metallic substrate. Carbtex fibers consisting in a thermoplastic core inside an oxidized outer shell (polyacrylonitrile or PAN fibers) are selected to make the NW. Measuring temperature profiles in a heat radiator test; it is revealed that Carbtex NW is an efficient heat barrier. A macroscopic model is then developed to simulate heat transfer in NW (considered as a porous medium) used as a protective heat barrier on aluminum plate. The model is validated comparing experimental results obtained by the heat radiator test and predicted values. The efficiency of NW layer is simulated varying different parameters characteristic of the NW (porosity and heat conductivity) and of the design (thickness of the layer). It is revealed to get good efficiency of the NW heat barrier that heat conductivity of the fibers is crucial to get superior performance as well as high porosity (higher than 0.5) associated with a reasonable thickness of NW (5,7 mm). © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 [source] Nonlinear refractive index of ceramic laser media and perspectives of their usage in a high-power laser-driverLASER PHYSICS LETTERS, Issue 10 2004Yu. Senatsky Abstract At the recent years a technology of ceramic laser media on the base of crystals with a cubic symmetry has been developed. The perspective of the usage of ceramic materials in many different applications including high - power short pulse lasers stimulates the work on the systematic study of the properties of these new laser media. A nonlinear refractive index, n2 was studied for several garnet and sesquioxide laser ceramics using Z-scan method. n2 indices in the range of (2 , 6) × 10,13 were measured for YAG, Y2O3, Lu2O3, and Sc2O3 ceramic samples. These data together with the other laser and spectroscopic parameters of several Nd3+ and Yb3+ doped crystals of a cubic symmetry were used to estimate the properties of laser ceramics for the application in a high-power pulsed-repetitive laser - driver for inertial confinement fusion (ICF) program. A high heat conductivity of ceramic materials is a profitable characteristic for this application as compared to glasses, which are used now for experiments in ICF at single shots regime. Compared to single crystals, ceramic elements provide laser designers with a variety of new design options for the projects of laser-drivers. (© 2004 by ASTRO, Ltd. Published exclusively by WILEY-VCH Verlag GmbH & Co. KGaA) [source] Nanostructured thermoelectric oxides with low thermal conductivityPHYSICA STATUS SOLIDI - RAPID RESEARCH LETTERS, Issue 6 2007A. Weidenkaff Abstract Complex metal oxides, such as e.g. perovskite-type phases are developed as potential functional materials to improve the efficiency of thermoelectric converters. Among those, cobaltates with p-type conductivity and n-type manganates are considered for the realisation of a ceramic thermoelectric converter. Sintered pellets with the composition AMO3,, (A = Ln, RE; M = Co, Mn, Ni, Ti) and "Ca3Co4O9 derivates" were synthesized and characterised concerning their thermoelectric properties in a broad temperature range. It was found that the Seebeck coefficient and the electrical conductivity do not depend on the dimensions of the crystallites, while the heat conductivity can be substantially lowered by decreasing the size of the crystalline domains in these systems. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Tayler instability with Hall effect in young neutron starsASTRONOMISCHE NACHRICHTEN, Issue 1 2009G. Rüdiger Abstract Collapse calculations indicate that the hot young neutron stars rotate differentially so that strong toroidal magnetic field components should exist in the outer shell where also the Hall effect appears to be important when the Hall parameter = ,B, exceeds unity. The amplitudes of the induced toroidal magnetic fields are limited by the current-induced Tayler instability. An important characteristics of the Hall effect is its distinct dependence on the sign of the magnetic field. We find for fast rotation that positive (negative) Hall parameters essentially reduce (increase) the stability domain. It is thus concluded that the toroidal field belts in young neutron stars induced by their differential rotation should have different amplitudes in both hemispheres which later are frozen in. Due to the effect of magnetic suppression of the heat conductivity also the brightness of the two hemispheres should be different. As a possible example for our scenario the isolated neutron star RBS 1223 is considered which has been found to exhibit different X-ray brightness at both hemispheres (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Permafrost Characteristics of the Qinghai-Tibet Plateau and Methods of Roadbed Construction of RailwayACTA GEOLOGICA SINICA (ENGLISH EDITION), Issue 5 2008NIU Fujun Abstract Permafrost along the Qinghai-Tibet railway is featured by abundant ground ice and high ground temperature. Under the influence of climate warming and engineering activities, the permafrost is under degradation process. The main difficulty in railway roadbed construction is how to prevent thawing settlement caused by degradation of permafrost Therefore the proactively cooling methods based on controlling solar radiation, heat conductivity and heat convection were adopted instead of the traditional passive methods, which is simply increasing thermal resistance. The cooling methods used in the Qinghai-Tibet railway construction include sunshine-shielding roadbeds, crushed rock based roadbeds, roadbeds with rock revetments, duct-ventilated roadbeds, thermosyphon installed roadbeds and land bridges. The field monitored data show that the cooling methods are effective in protecting the underlying permafrost, the permafrost table was uplifted under the embankments and therefore the roadbed stability was guaranteed. [source] | |||||||||||||