interpretation of "density ratio"

Dear all,
I did not understand the meaning of the "density ratio" parameter related to the quantities in the governing equations. I have found similar question in the archive of old forum but with no answers
[ July 19, 2006, 04:04:02 PM Doug Anderson][July 19, 2006, 03:58:05 PM Dwaine Edington].

In the documentation, the dependence of density on concentration is given by
rho = rho_0 + rho_0 * alpha_bar * (C - Co) / (Cs - Co)
but it is not written what is input as the "density ratio" in the user interface. There are two parameters, alpha_bar and Cs but only one input value (Co is input somewhere else and I do not find any reason for a nonzero value).
The only interpretation which makes sense is that I should input "alpha_bar/(Cs-Co)" in place of "density ratio". But the requested value of density ratio is dimensionless (with default 1e-4 multiplier) while "alpha_bar/(Cs-Co)" is not (alpha_bar is dimensionless).

Is it correct if I put "7" (i.e. 0.7e-3) as "density ratio" (according to above consideration) to have the simplest relation mentioned in the documentation rho(c)=rho_0 + 0.7 * c ? (considering rho_0=1000)

I have no idea how to check the results with a simple quantitative test problem with variable density. I did not find how to display density in the prostprocessing.

I work with 4.7 licence but it seems the interface is the same in higher versions.

Thank you for your help.
Milan Hokr

alpha_bar is the density ratio in FEFLOW. It has to be calculated by (rhos-rho0)/rho0, where rhos is the density at cs and rho0 is the density at rho0. cs is by default the maximum concentration in initial or boundary conditions (in later FEFLOW version cs can alternatively be set as a user-defined value). Please see also the attached Excel sheet for the basic calculations.