EOS4???????? linking between soil water contents and water vapor pressure in a thick unsaturated zone
Dear Stefan and other moderators
please i really need your help to figure out what is the best EOS
i have to consider the water vapor diffusion and its effects on the water contents with the time in a thick unsaturated zone
i mean consider the condensation of water vapor in the porous unsaturated zone and its effects on water contents and in other words i want a linking between soil water contents and the water vapor pressure, I am not sure if tough2 EOS4 ???? will do that or other EOS
please Stefan waiting for urgent replay suggest me the perfect EOS wich suits the situation best i hope i explained the situation in a good way
Thank you in advance
madi
20 replies
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Madi,
EOS4 it is!
Stefan
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Thanks a lot Stefan
Madi
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Dear Stefan,
one more question about the same topic as i explained before i will use EOS4
to consider the water vapor diffusion and its effects on water content in a thick vadose zone
which variable in the output of EOS4 file will express the mass fraction of diffusive water vapor if i am not wrong XAIRG will express the mass fraction of diffusive air not diffusive water vapor
to make it more clear i want to plot the concentration of diffusive water vapor against the distance from the groundwater table,
thank you very much in advance Stefan an i have to understand every detail before starting to compile EOS4.
MADI
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Madi,
I presume with "diffusive water vapor" you mean the mass fraction of the component water in the gas phase, which is simply 1-XAIRG.
Stefan
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Dear Stefan,
i want to ask you about the first primary variable which is Pg in eos3 or eos4
i think i have to calculate the Pg as a function of depth z
in the unsaturated zone(10 m thickness) 2 phase flow will be considered so my question Pg will be the capillary pressure is that correct? when i put it as atmospheric pressure no diffusion of water vapor was occurred (i am exercising first with Eos3 later will use eos4 )
thanks in advance
madi
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Hi Madi,
Pg is always the absolute (!) gas (or reference) pressure, not the capillary pressure, which is a secondary parameter calculated as a function of saturation. Note that water vapor diffusion is driven by a water-mass-fraction gradient in the gas phase, which (under two-phase conditions) occurs due to temperature differences or vapor pressure lowering effects, or if single-phase gas conditions exist.
Stefan
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Dear Stefan,
one more question to the same topic please
the second primary variable in EOS4 is Sg or gas saturation is it cosidered as(1-Sw) whereas Sw water saturation according to Van genuchten or others ..??
is it right?
or Sg is water vapor saturation which is a part from the total gas saturation i explained above
i am asking this question because i have got values of XAIRG in the output which indicate the water vapor diffusion as you told me in a previous post in the same topic about 0.98 which means very big values and never express the water vapor but the total gas content in the soil porous
i hope i have a good imagination of the situation
thanks in advance
Madi
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Madi,
Gas saturation is defined as the volumetric fraction of the gas phase in the pore space, so it is indeed 1-Sw. (Note that the definition is independent of the van Genuchten model.)
XAIRG is the mass fraction of the component air in the gas phase (= the mass of air in the gas phase divided by the total mass of the gas phase, which is the sum of the mass of air and mass of water vapor). Under atmospheric conditions, about 98% of the gas phase indeed consists of the pseudo-component "air", and only 1-XAIRG=XWATG=2% consists of water vapor, assuming 100% relative humidity.
Please consult the manual or http://esd.lbl.gov/files/research/projects/tough/support/initial-boundary-conditions.pdf for a description of the fundamental concepts.
Stefan
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Thank you Stefan for your very helpful remarks
all the Best,
Madi
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Dear Stefan,
as i explained in the previous posts i am doing the water vapour diffusion in 10 m unsaturated zone with eos4 when i run the model i had a problem that i could not solve why the PCAP capillary pressure in the output file are always zero in all time steps that is obviously wrong physically
i could not send the output file it is huge
Best,
Madi
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Dear Stefan,
i found the mistake it was only that in writing RPCAP
i wrote it PCAP only
if you donot mind could you please check the boundary conditions for me from above atmospheric with large volume element and from below i took two elements one at G water level and one 1 meter below ground water level i fixed these two elements or inactive them to make constant temperature and pressure
sorry again for disturbing you often and thanks in advance
Madi
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Dear Stefan according to the above question about the boundary conditions about the upper boundary condition i do not want to fix the values (make them constant)over my question must i set the volume of the atmospheric element in this case
later i have to put infiltration and evaporation rates i found in the literature you send me before
http://esd.lbl.gov/files/research/projects/tough/support/initial-boundary-conditions.pdf
"Specify infiltration rates in row of elements below the atmospheric
boundary element using the GENER block"if i do not want to make the atmospheric pressure and temperature fixed must i make this element in active and then GENER in the element below for infiltration
or make it active and GENER for the element below it or to delete the atmospheric boundary element and to applay the GENER on the element at the soil surface which is the first element then
thank you
madi
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Madi,
Just follow the instructions in the cited link. Essentially, the atmosphere is a Dirichlet b.c., so make it a large volume (as it is in reality!) or inactive; infiltration occurs at a prescribed rate, so it's a Neumann b.c. that goes into the second row (with active elements of finite volume) through the GENER block.
Good luck!
Stefan
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Dear Stefan
what i could not understand that when i put the the atmospheric element inactive or with large volume the temperature will be constant and equal to the initial value along the whole simulation and i can not consider the variation of temperature over time like when I isolate this section of earth from the variation in temperature over the time
could you please make it more clear
thanks
madi
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Dear Stefan
as a continuation to the previous post
i have just found the attached paper by chance
in this paper (Webb. W et al 2013) it was mentioned that there is another version of TOUGH2 which handles the variation in surface boundary conditions
i want to ask you if eos4 will do the variation over time in surface boundary conditions like the temperature etc, ..or i nead T2TNT (mentined in the attached paper) for this purpose and i have to link it with EOS4 for vapor pressure lowering effects( Kelvin s equation)
i really need your help to consider that
thanks in advance
Madi
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Madi,
Not clear whether (1) you want to specify the temperature in the atmosphere as a time-varying Dirichlet b.c. (in which case you would need a large volume), or (2) whether you want it to freely adjust given the soil temperature (which does not make much physical sense), or (3) whether you want the temperature in the top soil element not be affected by a prescribed atmosphere temperature. Webb's paper refers to (1), and it is an option that you could implement using standard TOUGH with large GENER (an option that is admittedly very awkward and difficult), or in case you had iTOUGH2 time-dependent Dirichlet b.c.s can easily provided in tabular form. Note that none of this is related to which EOS you're using.
Please describe in detail what boundary condition you want to employ.
Stefan
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Dear Stefan
i mean number (1) time varying b.c not only for the temperature in the atmosphere but also for other time dependent weather data like maybe radiation and relative humidity wend speed, precipitation all these together or at least some of them for long time series 2 or three year.. (i have to apply this to find finally how the diffusive water vapor affect the water content in a desert over the time)
i think it is impossible to put different time variables for long time series with daily recording(for example) all together in one large GENER
if you do not mind explain me the best way to set this upper boundary and if i need itough2 with its tabular property or it would be possible with normal TOUGH2 version# an what are your suggestions
thanks
Madi
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Madi,
I can only recommend iTOUGH2 or the implementation of the tabular feature into TOUGH2 - something I probably should be doing but won't have the time to do right away.
Which version of TOUGH2 do you have?
Stefan
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Dear Stefan,
i am using the normal TOUGH2, i checked an out put file it is version 2 as i can see
so, you mean i have to use itough2 in a forward way or you will do the tabular feature in the very soon future????
sorry i have no idea about itough2 are all EOS types included in it
sorry again for disturbing you quite often but really i want to learn from your experiences and to start my research correctly,
all the best,
madi
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Madi,
Yes, iTOUGH2 has all the EOSs, and you could use it in forward mode. However, I'll try to add the feature to regular TOUGH2, but cannot promise this will happen very soon, as I don' have time or funding for it. In the meantime, I suggest you set up your model using a time-constant atmospheric b.c. (or change it in a step fashion using the restart option, i.e., SAVE --> INCON) - there is plenty to be learned about this, and you can "debug" your model so it will be ready for detailed modeling of time-dependent b.c.
Stefan