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Calculator 17 - Effective Diffusion Calculator


EFFECTIVE DIFFUSION CALCULATOR


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The effective diffusion coefficient takes into account the fact that diffusion can only take place through pore openings because mineral grains block many of the possible pathways.

Cation Dd (10-6 cm2/s) Anion Dd (10-6 cm2/s)
H+ 93.1 OH- 52.7
Na+ 13.3 F- 14.6
K+ 19.6 Cl- 20.3
Rb+ 20.6 Br- 20.1
Cs+ 20.7 HS- 17.3
Mg2+ 7.05 HCO3- 11.8
Ca2+ 7.93 CO32- 9.55
Sr2+ 7.94 SO42- 10.7
Ba2+ 8.48    
Ra2+ 8.89    
Mn2+ 6.88    
Fe2+ 7.19    
Cr3+ 5.94    
Fe3+ 6.07  

 

Using these values, the effective diffusion coefficient can then be calculated using one of the following equations/calculators:

Greenkorn(1983)

Dd'=nDd

Where is an empirical value less than one, and n is porosity.

Dd   cm2/s

n

Dd':   cm2/s

 

Greenkorn & Kissler(1972)

Dd'=(n/)Dd

Where is tortuosity, which will be discussed in the next newsletter.

Dd   cm2/s

n

Dd':   cm2/s

 

Hellferich(1966)

The Hellferich equations give a range of values for the effective diffusion coefficient from:

Dd'=(n/2)Dd

to:

Dd'=(n/(2-n))2Dd

Dd   cm2/s

n

Dd': from to   cm2/s

References

Domenico P.A. and Schwartz, F.W. (1998). Physical and Chemical Hydrogeology. Published by John Wiley & Sons, Inc. New York, NY.

Fetter, C.W. (1994). Applied Hydrogeology; Third Edition.  Published by Prentice-Hall, Inc., Englewood Cliffs, NJ.

Freeze, R.A. and Cherry, J.A. (1979). Groundwater. Published by Prentice-Hall, Inc., Englewood Cliffs, NJ.



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