PhreeqcUsers Discussion Forum

Conceptual Models => Incorporation PHREEQC in programming languages => Topic started by: Zhaoyang on March 29, 2022, 01:54:03 PM

Title: Question about RM_SetComponentH2O
Post by: Zhaoyang on March 29, 2022, 01:54:03 PM
Dear all,

I am coupling a transport model with PhreeqcRM. However, I am confused about RM_SetComponentH2O in PhreeqcRM. In the transport model, water is reflected by pressure, whereas the concentration of water is needed when enabling RM_SetComponentH2O. Does anyone know how to deal with them when doing the coupling?
Thanks for your help in advance.

Best regards,
Title: Re: Question about RM_SetComponentH2O
Post by: dlparkhurst on March 29, 2022, 04:19:42 PM
To use PhreeqcRM, you must provide to the reaction module either (1) the total concentrations of H and O, including H and O in water [SetComponentH2O(false)], or (2) the concentration of liquid H2O, the concentration of non-water H ("excess H"), and the concentration of non-water O ("excess O") [SetComponentH2O(true)]. By experience, either choice seems to work. The reason for option 2 is that the excess quantities tend to be several orders of magnitude smaller than the total H an O, but accurate values of total H and O are needed to calculate pH and pe. It was reasoned that numerical errors in transporting the total H and total O could lead to inaccurate pH and pe, whereas transporting the excess quantities would be more accurate.

Usually, the concentrations [either choice (1) or (2)] are transported in the same way as other element concentrations.

Concentration options are mg/L, mol/L, or mass fraction (SetUnitsSolution).

Total moles of each element in a cell (used to define the solution in a cell in PhreeqcRM) depends on the concentrations of the elements plus the representative volume, porosity, and saturation of the cell.