[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: Phreeqci 2.6 charge balance question



Hello,

No, I don't think the program is calculating incorrectly.  I think I didn't
fully understand how the Advection keyword worked.  Realistically the
phenomena I was concerned about (solid phases resulting from the initial
condition dissolving) was very small after one pore volume and probably not
worth worrying about.  If I ran a large number of steps I think I'd get what
I'm looking for, but I think just running a few pore volumes through is
close enough.

I did try running ten separate simulations representating ten steps through
the reactor, where at each step I saved the solution and used it on the next
one, each time using the same set of equilibrium phases and reaction.  I got
pretty much the same answer.  The bad thing about this way is, I guess if I
use the selected output keyword to write to a spreadsheet, I would have to
write to ten separate spreadsheet files to save the results for plotting.  I
don't suppose there's a way for results from different simulations to be
written to the same spreadsheet file is there?

Thanks,
Brian Park

----- Original Message -----
From: "David L Parkhurst" <dlpark@xxxxxxxx>
To: "Brian Park" <bpark@xxxxxxxxxx>
Sent: Thursday, March 13, 2003 1:07 PM
Subject: Re: Phreeqci 2.6 charge balance question


>
> >What happens is, as the water flows through, various metals are
> precipitated
> as they should (Cu, Zn, Cd as sulfides, Al as hydroxide).  But eventually
> towards the end of the reactor the Cu/Zn/Cd concentrations increase
> slightly
> which should not happen - they should either decrease or stay the same,
not
> increase.  I have the equlibrium phase amounts set to zero, so that they
> should not dissolve but can precipitate if supersaturated.  It seems like
> during the advection sequence, the phase amounts for those metals get set
> to
> nonzero amounts, so that if conditions dictate they dissolve slightly.
>
> Right. If a phase precipitates during the simulation, it will redissolve
if
> conditions become undersaturated. I'm not sure why you think that the
> concentrations should not increase. Do you think the program is making an
> incorrect calculation? or that the program is calculating correctly, but
> you want to eliminate this effect in some way? My guess is that the
> calculations are done correctly, but perhaps there is an effect that you
> have not expected.
>
> >Is there a way to get around that with the advection keyword, to have
each
> shift contact equilibrium phases with zero amounts?  What I'm trying to do
> is predict water quality change as it flows through the reactor.
>
> Unfortunately, there is a dissolve_only option, but not a precipitate_only
> option. There is no easy way to do what you want. You could introduce
> kinetic reactions that precipitate the phases, but do not dissolve. This
> should work, but there can be problems if you try to make the rates fast
to
> simulate equilibrium. You can also redefine the EQUILIBRIUM_PHASES in the
> column, but at the extreme you would only run ADVECTION for one step at a
> time, redefine EQUILIBRIUM_PHASES, and then run another ADVECTION for
> another step.
>
> David
>
>
>
>
> David Parkhurst (dlpark@xxxxxxxx)
> U.S. Geological Survey
> Box 25046, MS 413
> Denver Federal Center
> Denver, CO 80225
>
> Project web page: http://wwwbrr.cr.usgs.gov/projects/GWC_coupled
>
>
>



Project Home Page
Complete Water Resources Division Software
USGS Home Page
Water Resources Division Home Page
NRP Home Page
Help Page
USGS Privacy Statement        Disclaimer

Please note that some U.S. Geological Survey (USGS) information accessed through this page may be preliminary in nature and presented prior to final review and approval by the Director of the USGS. This information is provided with the understanding that it is not guaranteed to be correct or complete and conclusions drawn from such information are the sole responsibility of the user.

Any use of trade, product, or firm names in this publication is for descriptive purposes only and does not imply endorsement by the U.S. Government. 


The URL of this page is: http://wwwbrr.cr.usgs.gov/projects/GWC_coupled/phreeqc/mail/msg00579.html
Email:dlpark@usgs.gov
Last modified: $Date: 2005-09-13 21:04:21 -0600 (Tue, 13 Sep 2005) $
Visitor number 1086 since Jan 22, 1998.