Hi,

I'm using FEFLOW to simulate coupled flow & mass&heat transport, with contrasting concentration values: at the top boundary (which corresponds to the sea bottom), a fixed (but flux-constrained) seawater (35 g/L) conc. is assigned, whereas the aquifer initial concentration is around 0 g/L. Density ratio was set to an appropriate value of 0.027.

I've read a bit about the non-Fickian dispersion type in FEFLOW offline help and in the FEFLOW Book, but I still don't understand how to define the value of the model parameter "Nonlinear dispersion" with its strange units (m2*s/kg). Can you explain me how to benefit from this advanced option (Nonlinear dispersion) within FEFLOW by putting good values for the new parameter? Thanks.

For those who are not familiar with this option, here is a short citation from FEFLOW help (in "Transport Settings"):
"Dispersion type: Besides the standard linear Fickian Bear-Scheidegger dispersion, FEFLOW supports a nonlinear dispersion relation. The nonlinear dispersion has shown to lead to more accurate results for density-dependent simulations with high-concentration gradients (brine transport)."
Hi,

The use of a non-Fickian dispersion has been observed relevant for systems with high-concentration differences, for example brine concentrations in deep aquifers or waste disposal in salt formations. This option can be activated directly in the Problem Settings - Transport Settings. Subsequently a parameter "Nonlinear dispersion" is available in the Data Panel in FEFLOW 6.2.

This high-concentration dispersion coefficient varies inversely to the flow velocity. In the FEFLOW Book you can find an analytical expression (Schotting et al. 1999) to calculate this parameter for a range of flow velocity from 10[sup]-5[/sup] and 10[sup]-3[/sup] m/s.

Further information can be found in sections 11.10.1, 11.10.3 and 11.11.6 in the FEFLOW Book.

Best regards,
Carlos

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