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81.
82.
Free-standing thick films of spinel ferrite, Ni0.89−xCu0.11ZnxFe2O4 with x=0.55 and 0.60, were prepared as fillers to fabricate electromagnetic composites. Compared to those made with conventional spherical fillers, the composites made with thick film fillers showed enhanced static permeability (μ′0) and maximum imaginary permeability (μ″max). At the same time, complex permittivity (ε′ and ε″) were almost unchanged. A relative bandwidth WR of 7–8 was achieved, which is about 75% of the theoretical maximum relative bandwidth. These composites are potential candidates as electromagnetic attenuation materials with ultrabroad absorption bandwidth in L and S bands. 相似文献
83.
The simple model of relativistic electron bremsstrahlung in a thin target is presented for conditions when its thickness less then a photon formation length. Results of our calculations obtained with account of an influence of target dielectric properties are in agreement with data at 25 GeV electron bremsstrahlung in thin layers of different media. 相似文献
84.
The reflection properties of planar anisotropy Fe50Ni50 powder/paraffin composites have been studied in the microwave frequency range.The permeability of Fe50Ni50 powder/paraffin composites is greatly enhanced by introducing the planar anisotropy,and can be further enhanced by using a rotational orientation method.The complex permeability can be considered as the superposition of two types of magnetic resonance.The resonance peak at high frequency is attributed to the natural resonance,while the peak at low frequency is attributed to the domain-wall resonance.The simulated results of the microwave reflectivity show that the matching thickness,peak frequency,permeability,and permittivity are closely related to the quarter wavelength matching condition.The Fe50Ni50 powder/paraffin composites can be attractive candidates for thinner microwave absorbers in the L-band(1-2 GHz). 相似文献
85.
Current models for pressure drop prediction of slug flow pneumatic conveying in a horizontal pipeline system assume some type of steady state conditions for prediction,which limits their capability for increased predictive accuracy relative to experimental data.This is partly because of the nature of slug flow pneumatic conveying system,which,as a dynamic system,never becomes stable.By utilising conservation of mass (airflow),a dynamic pressure analysis model is proposed on the basis of the derivative of the upstream pressure behaviour.The rate of air permeation through slug,one of the important factors in the conservation model,is expressed as a function of a slug permeability factor.Other factors such as slug velocity,slug length and the fraction of stationary layer were also considered.Several test materials were conveyed in single-slug tests to verify the proposed pressure drop model,showing good agreement between the model and experimental results. 相似文献
86.
James J. Sheng 《Transport in Porous Media》2009,77(3):507-527
To determine the permeabilities from a vertical interference test, earlier investigators proposed correlations or type curves
based on point source solutions or partially penetrated well solutions. However, it is impossible for these correlations or
type curves to cover all possible scenarios in the real world. In more recent years, people use regression analysis to simultaneously
match the pressure responses at the source interval and the observation point. With regression analysis, we face the problem
of non-unique solutions. Sometimes, estimated permeability could be outside a reasonable range when analyzing noisy data from
real tests. In this paper, a new technique is presented to estimate horizontal and vertical permeabilities from the time-delayed
response in a wireline vertical interference test. In a vertical test, a pressure drawdown test period is followed by a pressure
buildup test period. Because of the delay in response, the pressure at the observation probe continues to drop for some time
while the pressure at the source interval is being built up. The maximum pressure drop at the observation probe with regard
to the maximum pressure drop in the source interval is time-delayed. Using this time delay and the maximum pressure drop at
the observation probe, vertical and horizontal permeabilities can be estimated. A novel numerical scheme is used. The new
technique is compared with the previous methods, and it shows its superiority in accuracy. In addition, it can be used in
different test configurations. Application issues in real testing conditions are discussed. Finally, two field tests are analyzed
using this technique, while an earlier effort to analyze the tests using a conventional method was not successful due to poor
data quality. 相似文献
87.
The lattice Boltzmann method (LBM) is used to simulate the flow through an idealized proton exchange membrane fuel cell (PEMFC) porous transport layer (PTL) geometry generated using a Monte Carlo method. Using the calculated flow field, Darcy's law is applied and the permeability is calculated. This process is applied in both through‐ and in‐plane directions of the paper as both of these permeability values are important in computational fluid dynamics models of PEMFCs. It is shown that the LBM can be used to determine permeability in a random porous media by solving the flow in the microstructure of the material. The permeability in the through‐ and in‐plane directions is shown to be different and the anisotropic nature of the geometry creates anisotropic permeability. It is also found that fiber arrangement plays a large role in the permeability of the PTL. New correlations are presented for in‐ and though‐plane permeabilities of fibrous porous media with (0.6<ε<0.8). Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
88.
Anita Pti
ek Siro
i Ana Re
ek Zvonimir Katan
i Zlata Hrnjak-Murgi 《Molecules (Basel, Switzerland)》2021,26(11)
The studied samples were prepared from polyethylene (PE) polymer which was coated with modified polycaprolactone (PCL) film in order to obtain bilayer films. Thin PCL film was modified with casein/aluminum oxide compound to enhance vapor permeability as well as mechanical and thermal properties of PE/PCL films. Casein/aluminum oxide modifiers were used in order to achieve some functional properties of polymer film that can be used in various applications, e.g., reduction of water vapor permeability (WVTR) and good mechanical and thermal properties. Significant improvement was observed in mechanical properties, especially in tensile strength as well as in water vapor values. Samples prepared with aluminum oxide particles indicated significantly lower values up to 60%, and samples that were prepared with casein and 5% Al2O3 showed the lowest WVTR value. 相似文献
89.
Hydraulic permeability is studied in porous media consisting of randomly distributed monodisperse spheres by means of computational fluid dynamics (CFD) simulations. The packing of spheres is generated by inserting a certain number of nonoverlapping spherical particles inside a cubic box at both low and high packing fractions using proper algorithms. Fluid flow simulations are performed within the interparticulate porous space by solving Navier-Stokes equations in a low-Reynolds laminar flow regime. The hydraulic permeability is calculated from the Darcy equation once the mean values of velocity and pressure gradient are calculated across the particle packing. The simulation results for the pressure drop across the packing are verified by the Ergun equation for the lower range of porosities (<0.75), and the Stokes equation for higher porosities (∼1). Using the results of simulations, the effects of porosity and particle diameters on the hydraulic permeability are investigated. Simulations precisely specified the range of applicability of empirical or semi-empirical correlations for hydraulic permeability, namely the Carman-Kozeny, Rumpf-Gupte, and Howells-Hinch formulas. The number of spheres in the model is gradually decreased from 2000 to 20 to discover the finite-size effect of pores on the hydraulic permeability of spherical packing, which has not been clearly addressed in the literature. In addition, the scale dependence of hydraulic permeability is studied via simulations of the packing of spheres shrunk to lower scales. The results of this work not only reveal the validity range of the aforementioned correlations, but also show the finite-size effect of pores and the scale-independence of direct CFD simulations for hydraulic permeability. 相似文献
90.
The properties of polyurethane (PU) nanocomposites with three different organoclays were compared in terms of their thermal stabilities, mechanical properties, morphologies, and gas permeabilities. Hexadecylamine–montmorillonite, dodecyltrimethyl ammonium–montmorillonite, and Cloisite 25A were used as organoclays for making PU hybrid films. The properties were examined as a function of the organoclay content in a matrix polymer. Transmission electron microscopy photographs showed that most clay layers were dispersed homogeneously into the matrix polymer on the nanoscale, although some particles of clay were agglomerated. Moreover, the addition of only a small amount of organoclay was enough to improve the thermal stabilities and mechanical properties of PU hybrid films, whereas gas permeability was reduced. Even polymers with low organoclay contents (3–4 wt %) showed much higher strength and modulus values than pure PU. Gas permeability was reduced linearly with an increasing amount of organoclay in the PU matrix. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 670–677, 2002; DOI 10.1002/polb.10124 相似文献