			Home About us Contact

Low Aspect Ratio (low + aspect_ratio)

Distribution by Scientific Domains

Chemistry	40%

Selected Abstracts

Conductivity and Methanol Permeability of Nafion,Zirconium Phosphate Composite Membranes Containing High Aspect Ratio Filler Particles,

FUEL CELLS, Issue 4 2009
M. Casciola
Abstract Gels of exfoliated ,-zirconium phosphate (ZrPexf) in dimethylformamide (DMF) were used to prepare Nafion/ZrPexf composite membranes with filler loadings up to 7,wt.-% by casting mixtures of Nafion 1100 solutions in DMF and suitable amounts of 2,wt.-% ZrP gels in DMF. TEM pictures showed that the ZrPexf particles had aspect ratio of at least 20. All samples were characterised by methanol permeability (P) and through-plane (,thp) and in-plane (,inp) conductivity measurements at 40,°C and 100% RH. The methanol permeability of Nafion membranes containing in situ grown ZrP particles with low aspect ratio (Nafion/ZrPisg) was also determined. The methanol permeability and the swelling behaviour of the composite membranes turned out to be strongly dependent on the filler morphology. As a general trend, both permeability and swelling decreased according to the sequence: Nafion/ZrPisg > Nafion > Nafion/ZrPexf. The maximum selectivity (,thp/P,=,1.4,×,105,S,cm,3,s) was found for the membrane filled with 1,wt.-% ZrPexf: this value is seven times higher than that of Nafion. For the Nafion/ZrPexf membranes, the ratio ,inp/,thp increases with the filler loading, thus indicating that the preferred orientation of the ZrP sheets is parallel to the membrane surface. [source]

An approach to combined rock physics and seismic modelling of fluid substitution effects

GEOPHYSICAL PROSPECTING, Issue 2 2002
Tor Arne Johansen
ABSTRACT The aim of seismic reservoir monitoring is to map the spatial and temporal distributions and contact interfaces of various hydrocarbon fluids and water within a reservoir rock. During the production of hydrocarbons, the fluids produced are generally displaced by an injection fluid. We discuss possible seismic effects which may occur when the pore volume contains two or more fluids. In particular, we investigate the effect of immiscible pore fluids, i.e. when the pore fluids occupy different parts of the pore volume. The modelling of seismic velocities is performed using a differential effective-medium theory in which the various pore fluids are allowed to occupy the pore space in different ways. The P-wave velocity is seen to depend strongly on the bulk modulus of the pore fluids in the most compliant (low aspect ratio) pores. Various scenarios of the microscopic fluid distribution across a gas,oil contact (GOC) zone have been designed, and the corresponding seismic properties modelled. Such GOC transition zones generally give diffuse reflection regions instead of the typical distinct GOC interface. Hence, such transition zones generally should be modelled by finite-difference or finite-element techniques. We have combined rock physics modelling and seismic modelling to simulate the seismic responses of some gas,oil zones, applying various fluid-distribution models. The seismic responses may vary both in the reflection time, amplitude and phase characteristics. Our results indicate that when performing a reservoir monitoring experiment, erroneous conclusions about a GOC movement may be drawn if the microscopic fluid-distribution effects are neglected. [source]

Size-Dependence and Elasticity of Liquid-Crystalline Multiwalled Carbon Nanotubes,

ADVANCED MATERIALS, Issue 16 2008
Wenhui Song
Profound size-effects of liquid-crystalline microstructures of multiwalled carbon nanotube dispersions are reported. The figure shows that nanotubes behave like rigid rods in the case of a low aspect ratio; however, they behave as flexible beams that deform easily following the local orientation in a liquid crystalline field if they are thin and/or long with a relatively high aspect ratio. [source]

Initial stiffness of reinforced concrete structural walls with irregular openings

EARTHQUAKE ENGINEERING AND STRUCTURAL DYNAMICS, Issue 4 2010
Bing Li
Abstract Reinforced concrete (RC) structural walls with openings are the primary lateral-load-carrying elements utilized in many structures designed to resist earthquakes. A review of the technical literature shows that there is a considerable amount of uncertainty with regards to the elastic stiffness of these structures when subjected to seismic excitations. Current design practices often employ a stiffness reduction factor to deal with this uncertainty. In an attempt to develop additional information regarding the stiffness of these structures, this paper discusses an approach to determine the initial stiffness of RC structural walls with irregular openings and low aspect ratios. This approach would consider the effect of both flexural and shear deformations. As a part of this study, an analytical approach to determine stiffness was also developed and validated by comparing theoretical and experimental results obtained from six RC shear walls with irregular openings. Simple equations for assessing initial stiffness of RC structural walls with irregular openings are then proposed, based on these parametric case studies. Copyright © 2009 John Wiley & Sons, Ltd. [source]

Axial Dispersion and Wall Effects in Narrow Fixed Bed Reactors: A Comparative Study Based on RTD and NMR Measurements

CHEMICAL ENGINEERING & TECHNOLOGY (CET), Issue 8 2004
D. Tang
Abstract Axial dispersion and wall effects in narrow fixed beds with aspect ratios < 10 were investigated, both by classical methods and by NMR imaging. The residence time distribution (RTD) in the center and at the wall was measured, system water/NaCl-solution as tracer, and subsequently compared with radial velocity profiles based on NMR imaging. The influence of the aspect ratio and Rep on dispersion and on the degree of non-uniformity of the velocity profile was studied. The NMR results are consistent with the RTD and also with literature data of numerical simulations. For low aspect ratios, dispersion/wall effects have a strong influence on the reactor behavior, above all, in cases where a low effluent concentration is essential, as proven by breakthrough experiments with the reaction of H2S with ZnO. [source]