Processes > Reactive transport modelling

About the representative volume RV in PhreeqcRM

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cyprien:
Hi,

I am coupling PhreeqcRM with a finite volume transport solver. I am not sure to well understand what is the representative volume RV we have to specify. Is it the cell volume or is it something different that has to be equal to 1L?

Any light will be appreciated!
Thank you,
Cyprien

dlparkhurst:
PHREEQC works best if the mass of water is within an order of magnitude or two of 1 kg. PHAST uses one liter of aquifer as the representative volume, which results in a saturated water volume equal to the porosity. I think that is the simplest approach, but you can increase the representative volume, perhaps if the porosity is very small and conditions are unsaturated.

PhreeqcRM returns concentrations, so the extent of the representative volume is only important on the chemistry side for determining the amount of reactants (minerals, surfaces, exchangers, etc) available to react with the water in the representative volume.

cyprien:
Thank you for your prompt response.

In my case, I am interested in very fine grid block (in the order of cubic-micrometers), is it still correct to have RV = 1L ?

dlparkhurst:
Think so. Just get the right amounts of reactants.

Pak:
I am going to ask hre my question. Since I think that it is related somehow to this post. If somebody is against, please let me know and I will open a new thread and delete this post.

Does somebody know if the use of RM_SetPoreVolume, RM_SetSaturation, and RM_SetPorosity, has some effect if RM_UseSolutionDensityVolume has not been set?

So far, I have not found any change in using RM_SetPoreVolume, RM_SetSaturation, and RM_SetPorosity with different values (or even not setting RM_SetPoreVolume, RM_SetSaturation, and RM_SetPorosity), if RM_UseSolutionDensityVolume has not also been set.

There is a modification in the values of RM_GetSaturation, but it seem to me that is the only thing that is modified. The calculated concentrations are the same, and the RM_GetDensity and RM_GetSolutionVolume keep giving the same results.


Thank you for your help.

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