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Theoretical and numerical investigation of flow stability in porous materials applied as volumetric solar receivers 总被引:1,自引:0,他引:1
M. Becker Th. Fend B. Hoffschmidt R. Pitz-Paal O. Reutter V. Stamatov M. Steven D. Trimis 《Solar Energy》2006,80(10):1241-1248
This article reports results of a theoretical analysis as well as a numerical study investigating the occurrence of flow instabilities in porous materials applied as volumetric solar receivers. After a short introduction into the technology of volumetric solar receivers, which are aimed to supply heat for a steam turbine process to generate electricity, the general requirements of materials applied as solar volumetric receivers are reviewed. Finally, the main methods and results of the two studies are reported. In the theoretical analysis it is shown that heat conductivity as well as permeability properties of the porous materials have significant influence on the probability of the occurrence of flow instabilities. The numerical study has been performed to investigate the occurrence of unstable flow in heated ceramic foam materials. In the simulations a constant heat flow of radiation, that is absorbed in a defined volume, and constant permeability coefficients are assumed. Boundary conditions similar to those of the 10 MW Solucar Solar project have been chosen. In a three dimensional, heterogeneous two phase heat transfer model it was possible to simulate local overheating of the porous structure. The parameters heat conductivity, turbulent permeability coefficient and radial dispersion coefficient have been varied systematically. Consequently, for a heat flux density of 1 MW/m2 a parameter chart could be generated, showing the possible occurrence of “unstable” or “stable” thermal and fluid mechanical behaviour. These numerical results are beneficial for the design of optimized materials for volumetric receivers. 相似文献
74.
L. Bellot-Gurlet Th. Calligaro O. Dorighel J. -C. Dran G. Poupeau J. Salomon 《Nuclear instruments & methods in physics research. Section B, Beam interactions with materials and atoms》1999,150(1-4):616-621
In the present work we have coupled PIXE with fission track dating to characterise obsidian artefacts from about 40 archaeological sites of Colombia and Ecuador. PIXE analysis, carried out with the external beam line of the AGLAE tandem accelerator, yields the content in about 15 elements with Z > 8, whereas fission track dating is applied to ages in excess of about 10 000 years. About 120 artefacts were investigated by PIXE, of which 50 were dated by fission tracks. Ages and compositions were compared to those of obsidians from all known geological sources of the region. We show that this double characterisation allows us to determine the number of obsidian sources exploited in an ancient past and to give some insight into obsidian circulation. 相似文献
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Magnetic Resonance Materials in Physics, Biology and Medicine - To show the relevance of a simple finite difference transmission line model to help design safe implanted cables in 1.5T MRI’s... 相似文献
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R. Schneider J. Weder U. Coors G. -W. v. Rymon Lipinski R. Wittmann S. Wegner-Hambloch H. G. Kessler F. Ledl A. Rapp R. Frommberger Th. Täubert A. Rohrdanz D. Ehlermann D. v. Wachtendonk H. Weisser S. Scherer W. Ruge H. Klostermeyer H. Rehbein M. Miller H. G. Maier W. Feldheim F. Kiermeier J. Buchberger 《European Food Research and Technology》1991,193(6):566-574
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P Leterme A Théwis E Fran?ois P Van Leeuwen B Wathelet J Huisman 《Canadian Metallurgical Quarterly》1996,126(9):2188-2198
We assessed the use of 15N-labeled dietary proteins as a possible tool for the determination of the true ileal amino acid (AA) digestibility in pigs. The first experiment was designed to study the dietary N excretion pattern at the ileum subsequent to the ingestion of a single 15N-labeled meal. In a second experiment, we compared ileal endogenous AA outputs and true AA digestibility estimates obtained in pigs ingesting 15N-labeled dietary proteins in a single meal vs. intravenous infusion of [15N]leucine for 10 d during the ingestion of a pea-based diet and a protein-free starch diet. The proportion of endogenous N found in the ileal digesta differed when the label was delivered orally (50%) vs. intravenously (72%) and changed with time. As a consequence, the true ileal AA digestibilities measured with labeled diets were lower. A third experiment demonstrated that this was due to the rapid recycling of labeled dietary N in endogenous moieties, because 15N was found in blood within 10 min of consuming the labeled meal, within 50 min of consumption in pancreatic enzymes, 90 min in bile and 4 h in ileal mucins. We conclude that the use of 15N-labeled meals for determination of true ileal AA digestibilities is limited by the fast recycling of dietary N in endogenous secretions following a single 15N-labeled meal. The accuracy of results will depend on meaningful estimates of AA flow during a limited period and accurate estimates of 15N in AA. 相似文献
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W. Ensinger O. Lensch Th. Kraus Ch. Sundermann B. Enders 《Surface & coatings technology》2002,150(2-3):227-231
Tubes are often required to exhibit better performance in corrosion and wear behavior than the material the tube is made of can offer. The situation can be improved when the tube is coated with a protective film. This can be achieved by sputter coating with an ion beam. A sputter target is located inside the tube. Energetic ions are accelerated into the tube and impinge onto the target. Thus, material is sputtered from the target onto the inner walls of the tube. Two apparatus for coating tubes of different lengths and diameters are described. Aluminum and stainless steel tubes were coated with amorphous carbon films. Results on adhesion, corrosion performance in aqueous media and thickness uniformity are shown. 相似文献