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1.
The permeability of aromatic hydrocarbons, i.e. BTEX and styrene, through PVC pipes was investigated using a 6-cm pipe-bottle model with direct solid-phase microextraction (SPME) sampling. It was found that an aromatic hydrocarbon with a large molecular size or low polarity may be less permeable through PVC pipes. In addition, the diffusion coefficients of BTEX and styrene in PVC pipes ranged from 4.87 to 7.64 × 10−8 cm2/s. According to the simulation results of a one-dimensional diffusion model, it is speculated that diffusion transport of benzene and toluene in PVC pipes may have non-Fickian behavior. The advantage of using the innovated test model is that SPME provides a nondestructive analytical means to monitor the concentrations of organic compounds in pipe-water. Therefore, the pipe-bottle model developed herein has potential applications in determining the resistance of polymeric pipes to permeation by solvents in the aqueous solution. 相似文献
2.
Accuracy of the gas permeability parameters (GPPs), i.e. solubility, diffusivity and permeability deduced from permeation measurements, is investigated for the case of homogeneous polymer sheet samples. The widely used time-lag method (TLM) and the recently introduced full curve-fitting method (FCFM) are compared on simulated and on measured permeation curves artificially distorted in various ways in order to mimic potential deficiencies of permeation measurements. Accuracy of the methods is defined as the relative deviation of the calculated from the real GPPs, i.e. those which are deduced from the distorted and the original, non-distorted curves, respectively. The following distortions have been applied: temporal truncation of the permeation curves, increasing the noise level of the measurement and shifting the permeation curve either along the concentration or the time axis. (The latter two transformations correspond to an unnoticed background shift in the readings of the concentration detection unit and an uncertainty in the actual inception of the permeation process, respectively). While all these distortions mimic realistic deficiencies of permeation measurements, the last one is relevant only in case of fast permeation processes through highly permeable membranes. For all but the last transformation, FCFM has been found to yield more accurate GPPs than TLM. 相似文献
3.
4.
Morphological measurements in 3D for pore space characterization (connectivity pore-body/throat classification, shape factors,
virtual fluid intrusion) are based on computed intensive digital-thinning operations for skeletonization and medial axis extraction
from 3D digital images. We present an alternative method that is measurably faster and allows sub-voxel definition of the
pore space network. The method allows extracting—based on morphological considerations only—the centered and shortest stream-lines—i.e.,
the paths—to follow in order to go through the pore space from one given point to another and to exit. In addition the method
penalizes long and narrow pore-throats in favor of short stubby/ones—i.e., it has a built-in exemplification capacity. It
exploits well-established mathematical methods successfully applied in medical endoscopy. 相似文献
5.
In this paper a rigorous dual-porosity model is formulated, which accurately represents the coupling between large-scale fractures
and the micropores within dual porosity media. The overall structure of the porous medium is conceptualized as being blocks
of diffusion dominated micropores separated by natural fractures (e.g. cleats for coal) through which Darcy’s flow occurs.
In the developed model, diffusion in the matrix blocks is fully coupled to the pressure distribution within the fracture system.
Specific assumptions on the pressure behaviour at the matrix boundary, such as step-time function employed in some earlier
studies, are not invoked. The model involves introducing an analytical solution for diffusion within a matrix block, and the
resultant combined flow equation is a nonlinear integro-(partial) differential equation. Analyses to the equation in this
text, in addition to the theoretical development of the proposed model, include: (1) discussion on the “fading memory” of
the model; (2); one-dimensional perturbation solution subject to a specific condition; and (3) asymptotic analyses of the
“long-time” and “short-time” responses of the flow. Two previous models, the Warren-Root and the modified Vermeulen models,
are compared with the proposed model. The advantages of the new model are demonstrated, particularly for early time prediction
where the approximations of these other models can lead to significant error. 相似文献
6.
This paper presents a coupled model for anisotropic damage and permeability evolution by using a micro–macro approach. The damage state is represented by a second order tensor. The evolution of damage is determined from a crack propagation criterion. The free enthalpy function of cracked material is obtained by using micromechanical considerations. It is assumed that cracks exhibit normal aperture which is coupled with the crack growth due to asperities of crack faces. By using Darcy’s law for macroscopic fluid flow and assuming laminar flow in microcracks, the overall permeability of the RVE is obtained by a volume averaging procedure taking into account crack aperture in each orientation. 相似文献
7.
《Current Applied Physics》2020,20(5):638-642
A series of bio-silica incorporated barium-ferrite-composites with the composition of (x)Bio-SiO2:(80-x)γ-Fe2O3:(20)BaO, where x = 0, 1, 2, and 3 wt% were prepared using the modified solid-state reaction method. The influence of different bio-silica (extricated from sintered rice husk) contents on the surface morphologies, structures, and magnetic characteristics of these composites were assessed. The relative complex permittivity and permeability were resolved using the Nicholson-Ross-Weir strategy in the frequency range of 8–13 GHz. Meanwhile, the reflection loss was estimated through the transmission/reflection line theory to assess the MW absorption properties of the composites. Incorporation of the bio-silica in the barium ferrite composites generated a new hexagonal phase (Ba3Fe32O51) and a tetragonal phase (BaFeSi4O10) which led to a decrease in the saturation magnetization and significant shift in the MW frequency absorption peak positions. 相似文献
8.
The permeabilities of microscale fibrous porous media were calculated using the multiple-relaxation-time (MRT) lattice Boltzmann method (LBM). Two models of the microscale fibrous porous media were constructed based on overlapping fibers (simple cubic, body-centered cubic). Arranging the fibers in skew positions yielded two additional models comprising non-overlapping fibers (skewed simple cubic, skewed body-centered cubic). As the fiber diameter increased, the fibers acted as granular inclusions. The effects of the overlapping fibers on the media permeability were investigated. The overlapping fibers yielded permeability values that were a factor of 2.5 larger than those obtained from non-overlapping fibers, but the effects of the fiber arrangement were negligible. Two correlations were obtained for the overlapping and non-overlapping fiber models, respectively. The effects of the rarefaction and slip flow are also discussed. As the Knudsen number increased, the dimensionless permeability increased; however, the increase differed depending on the fiber arrangement. In the slip flow regime, the fiber arrangement inside the porous media became an important factor. 相似文献
9.
Ismayadi Ismail Mansor Hashim Khamirul Amin Matori Rosidah AliasJumiah Hassan 《Journal of magnetism and magnetic materials》2011,323(11):1470-1476
Ni0.5Zn0.5Fe2O4 has been synthesized using mechanical alloying method with two variables (milling time and ball-to-powder weight ratio (BPR)) were varied in order to study its effect on the magnetic properties of the material. The effects of these two variables were studied using XRD, SEM, TEM and later by impedance analyzer with the frequency range from 1 MHz to 1.8 GHz. The results obtained however show that there are no significant trends to relate the milling time and BPR with the permeability and losses of the material studied. After being sintered at 1150 °C, all the effects of alloying process seem to diminish. 相似文献
10.
E.J. Gutiérrez-Castañeda A. Salinas-Rodríguez 《Journal of magnetism and magnetic materials》2011,323(20):2524-2530
The effects of annealing prior to cold rolling on the microstructure, magnetic and mechanical properties of low-C grain non-oriented (GNO) electrical steels have been investigated. The grain structure of hot-rolled electrical steel strips is modified by annealing at temperatures between 700 and 1050 °C. Annealing at temperatures less than the ferrite to austenite+ferrite transformation temperature on heating (Ac1) causes a marginal effect on the grain size. However, annealing in the intercritical region at temperatures between Ac1 and Ac3 (the ferrite+austenite to austenite transformation temperature on heating) causes rapid decarburization and development of large columnar ferrite grains free of carbide particles. This microstructure leads, after cold rolling and a fast annealing treatment, to carbide free, large ferrite grain microstructures with magnetic and mechanical properties superior to those observed typically in the same steel in the industrially fully processed condition. These results are attributed to the increment in grain size and to the {1 0 0} fiber texture developed during the final annealing at temperatures up to 850 °C. Annealing at higher temperatures, T>Ac3, results in a strong {1 1 1} fiber texture and an increase of the quantity of second phase particles present in the microstructure, which lead to a negative effect on the final properties. The results suggest that annealing prior to cold rolling offers an attractive alternative processing route for the manufacture of fully processed low C GNO electrical steels strips. 相似文献