scholarly journals Time-Dependent Diffusion Coefficients for Chaotic Advection due to Fluctuations of Convective Rolls

Fluids ◽  
2018 ◽  
Vol 3 (4) ◽  
pp. 99 ◽  
Author(s):  
Kazuma Yamanaka ◽  
Takayuki Narumi ◽  
Megumi Hashiguchi ◽  
Hirotaka Okabe ◽  
Kazuhiro Hara ◽  
...  
Keyword(s):  
Diffusion Coefficient ◽  
Liquid Crystals ◽  
Diffusion Coefficients ◽  
Coarse Graining ◽  
Chaotic Advection ◽  
Time Dependent ◽  
Local Order ◽  
Weak Turbulence ◽  
Normal Diffusion ◽  
Convective Rolls

The properties of chaotic advection arising from defect turbulence, that is, weak turbulence in the electroconvection of nematic liquid crystals, were experimentally investigated. Defect turbulence is a phenomenon in which fluctuations of convective rolls arise and are globally disturbed while maintaining convective rolls locally. The time-dependent diffusion coefficient, as measured from the motion of a tagged particle driven by the turbulence, was used to clarify the dependence of the type of diffusion on coarse-graining time. The results showed that, as coarse-graining time increases, the type of diffusion changes from superdiffusion → subdiffusion → normal diffusion. The change in diffusive properties over the observed timescale reflects the coexistence of local order and global disorder in the defect turbulence.

scholarly journals The Effect of Particle Drag and Wall Absorption on Mass Transfer in Concentric Annulus Flows

2011 ◽  
Vol 10 (1) ◽  
pp. 1-13
Author(s):  
B. Umadevi ◽  
Dinesh P.A. ◽  
Indira R. Rao ◽  
Vinay C.V.
Keyword(s):  
Mass Transfer ◽  
Diffusion Coefficient ◽  
Diffusion Coefficients ◽  
Dispersion Model ◽  
Transport Coefficients ◽  
Time Dependent ◽  
Exchange Coefficient ◽  
Concentric Annulus ◽  
Annular Gap ◽  
And Diffusion

The effects of the irreversible boundary reaction and the particle drag on mass transfer are studied analytically in concentric annulus flows. The solution of mathematical model, based on the generalized dispersion model brings out the mass transport following by the insertion of catheter on an artery in terms of the three effective transport coefficients, viz., the exchange, convection and diffusion coefficient. A general expression is derived which shows clearly the time dependent nature of the coefficients in the dispersive model. The complete time dependent expression for the exchange coefficient is obtained explicitly and independent of velocity distribution in the flow; however it does depend on the initial solute distribution. Because of the complexity of the problem only asymptotic large time evaluations are made for the convective and diffusion coefficients, but these are sufficient to give the physical insight into the nature of the problem of the effects of drag and absorption parameters. It is found that as absorption parameter increases exchange and convection coefficients will be enhanced, but diffusion coefficient will be reduced. After certain period of time exchange coefficient will be constant for different values annular gap. As the drag parameter increases convection and diffusion coefficients will be reduced. With the enhancement of catheter radius i.e., the annular gap will be reduced then the convection and diffusion coefficients will be decreased.

Time-Dependent Non-Steady-State Diffusivities of C6 Paraffins in Silicalite by Zero-Length Column Method

1992 ◽  
Vol 57 (4) ◽  
pp. 698-709 ◽  
Author(s):  
Daniel Shavit ◽  
Patrick Voogd ◽  
Herman W. Kouwenhoven
Keyword(s):  
Diffusion Coefficient ◽  
Diffusion Coefficients ◽  
Reasonable Agreement ◽  
Time Dependent ◽  
Fast Diffusion ◽  
Diffusion Anisotropy ◽  
Zeolite Lattice ◽  
Column Method ◽  
Linear Isotherm ◽  
Long Time

Long-time diffusion experiments of n-hexane, 2-methylpentane and 2,3-dimethylbutane in silicalite according to the zero-length column method showed a significant decrease of the diffusion coefficients for longer times. A new and simple model of "uncoupled dual diffusion" is proposed to fit the experimental data. The calculated fast-diffusion coefficients as well as the calculated mean activation energies of diffusion of n-hexane and 2-methylpentane were almost equal and in reasonable agreement with literature data. A decrease of the adsorption partial pressure from 5.5 to 0.6 Torr did not have any influence on the fast-diffusion coefficient of n-hexane, which implies that the decrease of the diffusion coefficient in this range is not simply due to a non-linear isotherm. The proposed dual diffusion model may represent effects such as the presence of multiple energy states available for adsorbed molecules in the zeolite lattice, and/or diffusion anisotropy due to differences in the channel configurations in the three crystallografic directions.

scholarly journals Prediction of Time-Dependent Chloride Diffusion Coefficients for Slag-Blended Concrete

2017 ◽  
Vol 2017 ◽  
pp. 1-10 ◽  
Author(s):  
Ki-Bong Park ◽  
Han-Seung Lee ◽  
Xiao-Yong Wang
Keyword(s):  
Diffusion Coefficient ◽  
Diffusion Coefficients ◽  
Blended Cement ◽  
Numerical Procedure ◽  
Time Dependent ◽  
Chloride Diffusion ◽  
Chloride Diffusion Coefficient ◽  
Capillary Porosity ◽  
Key Factor ◽  
Hydration Model

The chloride diffusion coefficient is considered to be a key factor for evaluating the service life of ground-granulated blast-furnace slag (GGBS) blended concrete. The chloride diffusion coefficient relates to both the concrete mixing proportions and curing ages. Due to the continuous hydration of the binders, the capillary porosity of the concrete decreases and the chloride diffusion coefficient also decreases over time. To date, the dependence of chloride diffusivity on the binder hydration and curing ages of slag-blended concrete has not been considered in detail. To fill this gap, this study presents a numerical procedure to predict time-dependent chloride diffusion coefficients for slag-blended concrete. First, by using a blended cement hydration model, the degree of the binder reaction for hardening concrete can be calculated. The effects of the water to binder ratios and slag replacement ratios on the degree of the binder reaction are considered. Second, by using the degree of the binder reaction, the capillary porosity of the binder paste at different curing ages can be determined. Third, by using the capillary porosity and aggregate volume, the chloride diffusion coefficients of concrete can be calculated. The proposed numerical procedure has been verified using the experimental results of concrete with different water to binder ratios, slag replacement ratios, and curing ages.

Ansiotropy of the Diffusion Coefficient in Nematic Liquid Solutions Measured by NMR Techniques

1973 ◽  
Vol 28 (6) ◽  
pp. 964-967
Author(s):  
G. J. Krüger ◽  
H. Spiesecke
Keyword(s):  
Diffusion Coefficient ◽  
Liquid Crystals ◽  
Small Molecules ◽  
Diffusion Coefficients ◽  
Nematic Phase ◽  
Nematic Liquid Crystals ◽  
Gradient Coil ◽  
Liquid Solutions ◽  
Nmr Techniques ◽  
Relative Measurements

A gradient coil has been constructed for exact relative measurements of the longitudinal (Dʟ) and transverse (Dᴛ) diffusion coefficients of nematic liquid crystals and of small molecules dissolved therein. Some small molecules dissolved in the nematic phase of Licristal IV showed a Dʟ/Dᴛ ratio varying from about 1.1 to 1.25, depending on the concentration. In contrast, tetramethylsilane dis­solved in p-methoxy-benzylidene-p'-n-butyl-aniline showed no anisotropy in the nematic phase.

scholarly journals Effect of Modification on the Fluid Diffusion Coefficient in Silica Nanochannels

Molecules ◽  
2021 ◽  
Vol 26 (13) ◽  
pp. 4030
Author(s):  
Gengbiao Chen ◽  
Zhiwen Liu
Keyword(s):  
Diffusion Coefficient ◽  
Diffusion Coefficients ◽  
Surface Effect ◽  
Bulk Water ◽  
Self Diffusion ◽  
Average Diffusion Coefficient ◽  
Average Diffusion ◽  
Chain Lengths ◽  
Fluid Diffusion ◽  
Self Diffusion Coefficient

The diffusion behavior of fluid water in nanochannels with hydroxylation of silica gel and silanization of different modified chain lengths was simulated by the equilibrium molecular dynamics method. The diffusion coefficient of fluid water was calculated by the Einstein method and the Green–Kubo method, so as to analyze the change rule between the modification degree of nanochannels and the diffusion coefficient of fluid water. The results showed that the diffusion coefficient of fluid water increased with the length of the modified chain. The average diffusion coefficient of fluid water in the hydroxylated nanochannels was 8.01% of the bulk water diffusion coefficient, and the diffusion coefficients of fluid water in the –(CH2)3CH3, –(CH2)7CH3, and –(CH2)11CH3 nanochannels were 44.10%, 49.72%, and 53.80% of the diffusion coefficients of bulk water, respectively. In the above four wall characteristic models, the diffusion coefficients in the z direction were smaller than those in the other directions. However, with an increase in the silylation degree, the increased self-diffusion coefficient due to the surface effect could basically offset the decreased self-diffusion coefficient owing to the scale effect. In the four nanochannels, when the local diffusion coefficient of fluid water was in the range of 8 Å close to the wall, Dz was greater than Dxy, and beyond the range of 8 Å of the wall, the Dz was smaller than Dxy.

Time dependent diffusion coefficient in a disordered medium

1996 ◽  
Vol 104 (1) ◽  
pp. 206-209 ◽  
Author(s):  
Thomas M. de Swiet ◽  
Pabitra N. Sen
Keyword(s):  
Diffusion Coefficient ◽  
Time Dependent ◽  
Disordered Medium

Diffusion of Zinc in Two-Phase Mg-Al Alloy

2007 ◽  
Vol 263 ◽  
pp. 189-194
Author(s):  
Ivo Stloukal ◽  
Jiří Čermák
Keyword(s):  
Diffusion Coefficient ◽  
Diffusion Coefficients ◽  
Effective Diffusion ◽  
Residual Activity ◽  
Diffusion Path ◽  
Al Alloy ◽  
Serial Sectioning ◽  
Two Phase ◽  
Interphase Boundaries ◽  
The Mean

Coefficient of 65Zn heterodiffusion in Mg17Al12 intermetallic and in eutectic alloy Mg - 33.4 wt. % Al was measured in the temperature region 598 – 698 K using serial sectioning and residual activity methods. Diffusion coefficient of 65Zn in the intermetallic can be written as DI = 1.7 × 10-2 m2 s-1 exp (-155.0 kJ mol-1 / RT). At temperatures T ≥ 648 K, where the mean diffusion path was greater than the mean interlamellar distance in the eutectic, the effective diffusion coefficient Def = 2.7 × 10-2 m2 s-1 exp (-155.1 kJ mol-1 / RT) was evaluated. At two lower temperatures, the diffusion coefficients 65Zn in interphase boundaries were estimated: Db (623 K) = 1.6 × 10-12 m2 s-1 and Db (598 K) = 4.4 × 10-13 m2 s-1.

Sign in / Sign up

Export Citation Format

Share Document