scholarly journals Active Brownian particle in homogeneous media of different viscosities: numerical simulations

2021 ◽  
Author(s):  
E. A. Lisin ◽  
O. S. Vaulina ◽  
I. I. Lisina ◽  
O. F. Petrov
Keyword(s):  
Diffusion Coefficient ◽  
Brownian Motion ◽  
Numerical Simulations ◽  
Dynamic Viscosity ◽  
Effective Diffusion Coefficient ◽  
Brownian Particle ◽  
Effective Diffusion ◽  
Persistence Length ◽  
Active Brownian Particle ◽  
Homogeneous Media

Simple corrections are proposed to the basic theory of overdamped active Brownian motion, which allow one to calculate the effective diffusion coefficient and the persistence length of a self-propelled particle in a medium with any dynamic viscosity.

scholarly journals Effective diffusion coefficient of a Brownian particle in a periodically expanded conical tube

2013 ◽  
Vol 88 (5) ◽  
Author(s):  
Anatoly E. Antipov ◽  
Alexander V. Barzykin ◽  
Alexander M. Berezhkovskii ◽  
Yurii A. Makhnovskii ◽  
Vladimir Yu. Zitserman ◽  
...  
Keyword(s):  
Diffusion Coefficient ◽  
Effective Diffusion Coefficient ◽  
Brownian Particle ◽  
Effective Diffusion ◽  
Conical Tube

Diffusion of Heavy Oil in SiO2 Model Catalyst and FCC Catalyst

2012 ◽  
Vol 550-553 ◽  
pp. 158-163 ◽  
Author(s):  
Zi Yuan Liu ◽  
Sheng Li Chen ◽  
Peng Dong ◽  
Xiu Jun Ge
Keyword(s):  
Diffusion Coefficient ◽  
Pore Size ◽  
Effective Diffusion Coefficient ◽  
Pore Diameter ◽  
Effective Diffusion ◽  
Model Catalyst ◽  
Average Pore ◽  
Diffusion Factor ◽  
Fcc Catalyst ◽  
Fcc Catalysts

Through the measured effective diffusion coefficients of Dagang vacuum residue supercritical fluid extraction and fractionation (SFEF) fractions in FCC catalysts and SiO2model catalysts, the relation between pore size of catalyst and effective diffusion coefficient was researched and the restricted diffusion factor was calculated. The restricted diffusion factor in FCC catalysts is less than 1 and it is 1~2 times larger in catalyst with polystyrene (PS) template than in conventional FCC catalyst without template, indicating that the diffusion of SFEF fractions in the two FCC catalysts is restricted by the pore. When the average molecular diameter is less than 1.8 nm, the diffusion of SFEF fractions in SiO2model catalyst which average pore diameter larger than 5.6 nm is unrestricted. The diffusion is restricted in the catalyst pores of less than 8 nm for SFEF fractions which diameter more than 1.8 nm. The tortuosity factor of SiO2model catalyst is obtained to be 2.87, within the range of empirical value. The effective diffusion coefficient of the SFEF fractions in SiO2model catalyst is two orders of magnitude larger than that in FCC catalyst with the same average pore diameter. This indicate that besides the ratio of molecular diameter to the pore diameter λ, the effective diffusion coefficient is also closely related to the pore structure of catalyst. Because SiO2model catalyst has uniform pore size, the diffusion coefficient can be precisely correlated with pore size of catalyst, so it is a good model material for catalyst internal diffusion investigation.

scholarly journals Restricted diffusion of model sulfides over a NiMo/BK catalyst under hydrodesulfurization reaction conditions

RSC Advances ◽  
2017 ◽  
Vol 7 (70) ◽  
pp. 44340-44347 ◽  
Author(s):  
Huadong Wu ◽  
Aijun Duan ◽  
Zhen Zhao ◽  
Chunming Xu ◽  
Guiyuan Jiang ◽  
...  
Keyword(s):  
Diffusion Coefficient ◽  
Effective Diffusion Coefficient ◽  
Effective Diffusion ◽  
Molecular Size ◽  
Restricted Diffusion ◽  
Reaction Conditions ◽  
Effective Factors

The effective factors (η) of a NiMo/BK catalyst are greater than that of the traditional NiMo/Al2O3; the effective diffusion coefficient (De) decreases with the increasing molecular size of the model sulfides.

scholarly journals Characterization of Effective Diffusion within Viscoelastic Fluids with Elastic Instabilities

Fluids ◽  
2022 ◽  
Vol 7 (1) ◽  
pp. 33
Author(s):  
Valerie Hietsch ◽  
Phil Ligrani ◽  
Mengying Su
Keyword(s):  
Diffusion Coefficient ◽  
Couette Flow ◽  
Effective Diffusion Coefficient ◽  
Effective Diffusion ◽  
Flow Shear ◽  
Shear Rates ◽  
Flow Environment ◽  
Disk Rotation ◽  
Elastic Instabilities ◽  
Fluorescein Dye

We considered effective diffusion, characterized by magnitudes of effective diffusion coefficients, in order to quantify mass transport due to the onset and development of elastic instabilities. Effective diffusion coefficient magnitudes were determined using different analytic approaches, as they were applied to tracked visualizations of fluorescein dye front variations, as circumferential advection was imposed upon a flow environment produced using a rotating Couette flow arrangement. Effective diffusion coefficient results were provided for a range of flow shear rates, which were produced using different Couette flow rotation speeds and two different flow environment fluid depths. To visualize the flow behavior within the rotating Couette flow environment, minute amounts of fluorescein dye were injected into the center of the flow container using a syringe pump. This dye was then redistributed within the flow by radial diffusion only when no disk rotation was used, and by radial diffusion and by circumferential advection when disk rotation was present. Associated effective diffusion coefficient values, for the latter arrangement, were compared to coefficients values with no disk rotation, which were due to molecular diffusion alone, in order to quantify enhancements due to elastic instabilities. Experiments were conducted using viscoelastic fluids, which were based on a 65% sucrose solution, with different polymer concentrations ranging from 0 ppm to 300 ppm. Associated Reynolds numbers based on the fluid depth and radially averaged maximum flow velocity ranged from 0.00 to 0.5. The resulting effective diffusion coefficient values for different flow shear rates and polymer concentrations quantified the onset of elastic instabilities, as well as significant and dramatic changes to local mass transport magnitudes, which are associated with the further development of elastic instabilities.

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