Gas Diffusion and Re-Diffusion in Polyethylene Foams

2009 ◽  
Vol 283-286 ◽  
pp. 583-588
Author(s):  
J. Escudero ◽  
J. Lázaro ◽  
E. Solórzano ◽  
Miguel A. Rodríguez-Pérez ◽  
Jose A. de Saja
Keyword(s):  
Diffusion Coefficient ◽  
Diffusion Process ◽  
Static Loading ◽  
Effective Diffusion Coefficient ◽  
Effective Diffusion ◽  
Gas Diffusion ◽  
Low Density Polyethylene ◽  
Low Density ◽  
Compressive Creep ◽  
Closed Cell

In this work, the effective diffusion coefficient of the gas contained in closed cell polyethylene foams under static loading is measured. To do this, compressive creep experiments were performed on low density polyethylene foams produced under a gas diffusion process. Density dependence of this coefficient has been analysed as well as the variation of pressure with time inside the cells. Finally, immediately after compressive creep, the recovery behaviour of the foams was also characterised. Different abilities for recovering were observed depending on the density of the foam and the absolute recovery resulted independent of the initial stress applied.

Enhanced Diffusion Due to Swimming Bacteria

2003 ◽  
Author(s):  
Min Jun Kim ◽  
Kenneth S. Breuer
Keyword(s):  
Escherichia Coli ◽  
Molecular Weight ◽  
Diffusion Coefficient ◽  
Diffusion Process ◽  
Effective Diffusion Coefficient ◽  
Effective Diffusion ◽  
Flow Cell ◽  
Fickian Diffusion ◽  
Enhanced Diffusion ◽  
Swimming Bacteria

The effect of bacterial motion of the diffusion of a high molecular weight molecule is studied by observing the mixing of two streams of fluid in a micro-fabricated flow cell. The presence of Escherichia coli (E.coli) in one of the streams results in an increase in the effective diffusion coefficient of Dextran, which rises linearly with the concentration of bacteria from a baseline value of 2 × 10−7 cm2/s to 8 × 10−7 cm2/s at a concentration of 2.1 × 109 /ml (approximately 0.5 % by volume). The diffusion process is also observed to undergo a change from standard “Fickian” diffusion to a superdiffusive behavior in which the diffusion exponent rises from 0.5 to 0.55 as the concentration of bacteria rises from 0 to 2.1 × 109/ml.

Rapid, Steady-State Measurement of the Effective Diffusion Coefficient of Gases in Closed-Cell Foams

1988 ◽  
Vol 110 (2) ◽  
pp. 500-506 ◽  
Author(s):  
A. G. Ostrogorsky ◽  
L. R. Glicksman
Keyword(s):  
Diffusion Coefficient ◽  
Steady State ◽  
Diffusion Coefficients ◽  
Effective Diffusion Coefficient ◽  
Effective Diffusion ◽  
Polyurethane Foams ◽  
New Technique ◽  
Closed Cell ◽  
State Technique

A rapid steady-state technique was developed to measure the effective permeability and diffusion coefficients of closed-cell foam insulation. To test the new technique, N2 data were first obtained by the long-term steady-state technique, and then reproduced ten times faster by the rapid steady-state technique. By using the new technique, reference values of effective diffusion coefficients of N2, O2, and Fluorocarbon 11 in closed-cell polyurethane foams were obtained at different temperatures. Data for Fluorocarbon 11 were obtained 30 times faster than data could be obtained by long-term steady-state tests. To estimate when steady-state has been achieved, the transient diffusion equation was solved, and the solution was given in the form of a chart. The time needed to achieve steady-state mass flux in a foam sample was found to depend strongly on the ratio of the partial pressures imposed on the surface of a tested sample. By use of the solution, the value of the foam effective diffusion coefficient can be obtained before steady-state conditions are achieved within the sample.

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.

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