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Various Geometries (various + geometry)
Selected AbstractsCoupled lubrication and Stokes flow finite elementsINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 2 2003Matthew S. Stay Abstract A method is developed for performing a local reduction of the governing physics for fluid problems with domains that contain a combination of narrow and non-narrow regions, and the computational accuracy and performance of the method are measured. In the narrow regions of the domain, where the fluid is assumed to have no inertia and the domain height and curvature are assumed small, lubrication, or Reynolds, theory is used locally to reduce the two-dimensional Navier,Stokes equations to the one-dimensional Reynolds equation while retaining a high degree of accuracy in the overall solution. The Reynolds equation is coupled to the governing momentum and mass equations of the non-narrow region with boundary conditions on the mass and momentum flux. The localized reduction technique, termed ,stitching,' is demonstrated on Stokes flow for various geometries of the hydrodynamic journal bearing,a non-trivial test problem for which a known analytical solution is available. The computational advantage of the coupled Stokes,Reynolds method is illustrated on an industrially applicable fully-flooded deformable-roll coating example. The examples in this paper are limited to two-dimensional Stokes flow, but extension to three-dimensional and Navier,Stokes flow is possible. Copyright © 2003 John Wiley & Sons, Ltd. [source] The geometrical design of membraneless micro fuel cells: Failure and successINTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 10 2010Dewan Hasan Ahmed Abstract A comprehensive numerical study of membraneless micro fuel cells with various geometries is carried out with the aim of reducing the mixing of the anode and cathode fluids and increasing their fuel utilization. Designs with blocks or obstacles in the main channel or a main channel with a wavy shape result in very little improvement in these properties or even in their deterioration. However, some designs with other types of channel cross-section exhibit much less mixing of the two fluids in the main channel. In particular, an octagonal cross-section is found to result in better performance. However, the difficulty of the micro fabrication of fuel cells with this design encourages us to test two other geometries for the cross-section: H-shaped and trident-shaped. The H-shaped cross-section exhibits much less mixing in the main channel and much higher fuel utilization. The fuel cell with a trident-shaped cross-section has two inlets for the anode and cathode fluids and a third inlet for the proton-conducting fluid, and is found to be the best design in that the anode and cathode fluids are more restricted to their respective electrodes (reaction surfaces). Further, in this design the reactants cover only 40% of the channel width, which is much less than in the other designs, and maximum fuel utilization is obtained. The failure and success cases will guide for future geometrical design of any micro fluidic devices where mixing and non-mixing issues are the major concerns. The present numerical results are validated by comparison with literature data. Copyright © 2009 John Wiley & Sons, Ltd. [source] Parameters affecting the full-shot molding of gas-assisted injection-molded partsADVANCES IN POLYMER TECHNOLOGY, Issue 1 2003Shih-Jung Liu Abstract Full-shot gas-assisted injection-molding has the advantage of eliminating the switchover mark that usually occurs on the surface of short-shot gas-assisted molded parts. The purpose of this report was to study the effects of processing parameters on the moldability of the full-shot gas-assisted injection-molding process. Experiments were carried out on an 80-ton injection-molding machine equipped with a high-pressure nitrogen-gas injection unit. The materials used were general-purpose polystyrene and polypropylene. A plate cavity with a gas channel of various geometries (trapezoid, semicircle, and rectangle) across the center was used to mold the parts. After molding, the lengths of gas penetration were determined. The hollowed core ratio by the gas was also determined. A numerical analysis was carried out to find out the temperature distribution of the polymer melt inside the gas channel. It was found that the sink mark of molded parts decreases with the length of gas penetration. Molded parts using trapezoidal gas channel had the longest gas penetration length. In addition, a thermal contraction model was proposed to predict the gas penetration volume inside the parts. Good agreement was reached between the experimental data and the calculated result. © 2003 Wiley Periodicals, Inc. Adv Polym Techn 22: 1,14, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/adv.10036 [source] Poly[1-(trimethylgermyl)-1-propyne] and poly[1-(trimethylsilyl)-1-propyne] with various geometries: Their synthesis and propertiesJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 14 2003V. S. Khotimsky Abstract The polymerization of 1,2-disubstituted acetylenes [1-(trimethylgermyl)-1-propyne and 1-(trimethylsilyl)-1-propyne] initiated by Nb- and Ta-based catalytic systems was studied within a wide temperature range (,10 to +80 °C) with solvents (cyclohexane, CCl4, toluene, anisol, and n -chlorobutane) with variable dielectric constants (2.023,7.390). Conditions ensuring the synthesis of poly[1-(trimethylsilyl)-1-propyne] (PTMSP) containing 20,80% cis units and poly[1-(trimethylgermyl)-1-propyne] (PTMGP) containing 3,65% cis units were determined. The PTMSP and PTMGP samples were amorphous, exhibited a two-phase structure characterized by the presence of less ordered regions and regions with an enhanced level of ordering, and differed in solubility. A correlation was found between the cis/trans ratio and the morphology, the geometrical density of PTMSP and PTMGP films, and the gas permeability of the polymers. The gas permeability and solubility behavior of PTMSP and PTMGP were examined in terms of the molecular characteristics of the polymer samples (the thermodynamic Kuhn segment and the Kerr electrooptic effect). It was demonstrated that the gas permeability, as well as the solubility of the polymers, was defined by their supramolecular ordering, which depended on the lengths of continuous sequences composed of units of analogous microstructures and on the flexibility of macrochains. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 2133,2155, 2003 [source] Versatile Crack-Free Ceramic Micropatterns Made by a Modified Molding TechniqueJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 9 2010Marzellus Grosse Holthaus Crack-free ceramic micropatterns made of oxidic ceramic powders, e.g. alumina, titania, zirconia, and nonoxidic calciumphosphate ceramic powders were fabricated by a novel, simple, and low-cost modified micromolding (m-,M) technique via polydimethylsiloxane stamps. By means of this m-,M technique it is possible to fabricate monolithic ceramic bodies with a micropatterned surface with very high accuracy on surface detail. Our produced micropatterns can feature various geometries, e.g. cylinders, holes, channels, and struts with diameters ranging from 8 to 140 ,m in diameter or widths and from 8 to 30 ,m in depth or height. The oxidic and nonoxidic ceramic micropatterns could be removed from the molds and dried without any cracks. Even after sintering, these micropatterned samples showed no cracks or fissures. The reported technique has a very high potential for fully automatized up-scale fabrication of micropatterned ceramic surfaces. [source] Alkynyl Ethers of Glucans: Substituent Distribution in Propargyl-, Pentynyl- and Hexynyldextrans and -amyloses and Support for Silver Nanoparticle Formation,MACROMOLECULAR CHEMISTRY AND PHYSICS, Issue 15 2010M. Nazir Tahir Abstract Alkynyldextrans with a DS in the range 0.1,1.67 have been prepared as reactive intermediates for further polymer-analogous functionalisation. DS and substituent distribution were determined by GLC and GLCMS after hydrolysis and acetylation, or methanolysis and trimethylsilylation. Reactivity was in the order O-2,>,O-4,,,O-3 with pronounced differences in the distinct patterns for propargyl ethers and its higher homologous. A large deviation from a random substituent distribution was observed. Propargyldextrans were not stable during long-time storage in the solid state, while terminal pentynyl and hexynyl ethers are. Pentynyldextrans showed structure formation of various geometries. They bound silver efficiently, yielding silver nanoparticles by reduction. [source] Optically and electrically induced dissipation in quantum Hall systemsPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 2 2008G. Nachtwei Abstract We have studied the onset of dissipation in quantum Hall systems (QHSs), patterned in various geometries (Hall bars, meanders and Corbino rings) from wafers with heterojunctions (GaAs/GaAlAs) and HgTe quantum wells with adjacent HgCdTe barriers. The QH samples were excited by electrical pulses with pulse durations tP of 0.5 ns , tP , 180 ns or by illumination with electromagnetic waves of 1.7 THz , f , 2.5 THz. These waves were either emitted coherently by a pulsed p-Ge laser system or by a thermal source. In the case of excitation by electric pulses, it is necessary to exceed a certain critical pulse length which is a function of various extrinsic parameters and sample properties. For no dissipation occurs inside the QHSs. Also, using THz illumination, the QHSs can be driven to dissipation. We found different mechanisms to be responsible for the photoresponse (PR) of the QHSs: non-resonant (bolometric) and resonant (cyclotron resonance) contributions to the PR of the QHSs. First attempts to develop a quantitative model for the observed data are made. We are able to describe a part of the observations by either a drift model or a two-level model. The quantitative agreement of these calculations with the measured data is, however, limited. This is due to the simplicity of the models applied so far and to the complex behaviour of QHSs when nonlinearly excited. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Commercial applications of porous Si: optical filters and componentsPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 6 2007V. Kochergin Abstract It is shown that porous Silicon in various geometries and morphologies can be used for novel optical elements by combining theoretical insights with suitable porous structures and some pre- and post-processing of the Silicon. The paper restricts itself to light propagation in the pore direction. Theoretical and experimental results will be presented for the following novel optical elements: environmentally stable optical components from mesoporous Silicon, long wave pass filters, macroporous Silicon UV Filters, and polarization components for the UV range. Either new components are presented, mostly with first experimental results, or the state-of-the art for previously discussed elements is considerably improved upon. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] | ||||||||||||||||