Applications of the fractal theory to analyze transport properties of porous media in science and engineering have received steady attention in the past two decades. However, the theory was rarely ...used to analyze invasion by extraneous fluids into a permeable bed where there is initially no such fluid present. Spills and leaks of non-aqueous phase liquids (NAPLs) and formation damage in drilling and completion wells are two typical examples. In this work, a fractal capillary model is proposed to analyze the depth of extraneous fluid invasion, where the tortuosity of capillaries and capillary pressure effect are taken into account. The quantitative relationship between average flow velocity and average beeline velocity are discussed based on the fractal geometry theory. Based on the proposed model, the depth of extraneous fluid invasion can be determined when the operation conditions, extraneous fluid properties and formation structure parameters are available, and the model predictions are in good agreement with the available data.
Gas diffusion in nanofibrous and microfibrous materials is of great interest in microfluidics. In this work, an analytical model is proposed, based on fractal theory, to quantify gas diffusion across ...fibrous media composed of nanofibers and microfibers. The fractal model is expressed in terms of pore area and tortuosity fractal dimensions, allowing statistical quantification of the geometrical structures of fibrous media. Knudsen diffusion in nanoscale pores is considered. To validate this model, moisture vapor diffusion rate through electrospun nanofibrous webs was measured using the inverted-cup method. The diffusivities predicted from the proposed model agree well with the experimental measurements in the present investigation and those reported in the literature for effective diffusivities of gas diffusion layers in fuel cells. Based on the model, the effect of porosity, fiber radius, and the ratio between the minimum and the maximum pore sizes on the effective diffusivity is analyzed.
Both face and back sides of cotton weft-knitted fabrics in five knitting structures (plain, rib, interlock, single pique, and double pique) were investigated based on modified water drop test ...(methods I and II) in terms of water diffusion time. The water drop height was raised from 1 cm to 20 cm and water drop volume was increase from 0.1 mL to 0.5 mL. The water diffusion time greatly decreased with the variation in water drop height from 0 to 15 cm. Water diffusion time was also influenced by water volume at 0.1-0.2 mL for the different structures and surfaces. It was found that the structures behaved differently, and two surfaces of fabric were capable of asymmetric water absorption property. The face side of single pique and the back side double pique had better water diffusion property. Besides, vertical wicking rate and the drying rate (methods I and II) were also conducted to evaluate the different structures. Although the plain structure was widely used for inner garments in the market, the interlock fabric was recommended in nonsweating conditions due to its poor water spreading and better drying ability, while the single-pique fabric was recommended in heavy sweating conditions due to its better water absorption ratio and faster drying rate.
Based on the intrinsic growth rate (
R
∼
T
1/3) of single droplet, processes of nucleation, growth, renucleation and sweeping of droplet are simulated in this paper. The influences of number of ...initial droplets on average radius, surface coverage and number of droplets on substrate are investigated. The simulation results show that the apparent growth rate of droplets is strongly dependent on the number of initial droplets. In addition, statistical fractal characteristic of droplet size distribution is found to be consistent with experimental measurements, and the drop size distribution is also found to be consistent qualitatively with that from experimental observations. The validity of the present simulations is thus verified. The present work may provide a great help in well understanding of the growth mechanism of dropwise condensation.
Energy levels, transition rates, and lifetimes are reported for the low-lying 129 levels of Fe XIV, belonging to the
n
= 3 states (1
s
2
2
s
2
2
p
6
)3
s
2
3
p
, 3
s
3
p
2
, 3
s
2
3
d
, 3
p
3
, 3
s
3
...p
3
d
, 3
p
2
3
d
, 3
s
3
d
2
, and 3
p
3
d
2
. High-accuracy calculations have been performed as benchmarks in the request for accurate treatments of relativity, electron correlation and quantum electrodynamic (QED) effects in multi-valence-electron systems. The calculated energy levels are in excellent agreement with the experimental results and the experimentally compiled energy values, of the National Institute for Standards and Technology wherever available. The calculated values including core–valence correlation are found to be in good agreement with other theoretical and experimental values.
Energy levels among the lowest 40 fine-structure levels in Be-like Mg IX are calculated using grasp2K code. The wavelengths, oscillator strengths, radiative rates and lifetimes for all possible
K
α
...transitions have been calculated using the multiconfiguration Dirac–Fock method. The accuracy of the results is determined through extensive comparisons with the existing laboratory measurements and theoretical results. The present data can be used reliably for many purposes, such as the line identification of the observed spectra, and modelling and diagnostics of magnesium plasma.
In this paper, a fractal model for dropwise condensation heat transfer is developed based on the fractal characteristics of drop size distributions on condensing surfaces. Expressions for the fractal ...dimension and area fraction of drop sizes are derived, which are shown to be a function of temperature difference between condensing surface and saturated vapor. The condensation heat transfer is found to be a function of the fractal dimension for drop sizes, maximum and minimum drop radii, the temperature difference, and physical properties of fluid. The predicted total heat flux from a condensing surface based on the present fractal model is compared with existing experimental data. Good agreement between the model predictions and experimental data is found, which verifies the validity of the present model.
Plasmonically induced transparency (PIT) effect in a metal–insulator–metal waveguide coupled to asymmetric multi-rectangle resonators is investigated numerically. By adjusting parameters of ...resonators, we cannot only realize single, double, or treble PIT peaks in the compact structure, but also induce an off-to-on PIT optical response. Numerical simulation by finite element method was conducted to verify our designs. This proposed structure, hence has potential applications for ultra-compact optoelectronic devices at communication band.
Symmetry is not always prefect Luo, Liang; Yu, Boming; Cai, Jianchao ...
International journal of heat and mass transfer,
10/2010, Letnik:
53, Številka:
21
Journal Article
Recenzirano
This paper discusses the effect of bifurcation structures on flow resistance of the two-bifurcation network, which satisfies Murray’s law. The asymmetrical and symmetrical two-bifurcation networks ...with the same number and diameter of the terminal branches are compared, and the results show that the symmetrical two-bifurcation network is not the best for transport in it.
