1

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

20replies Oldest first
• Oldest first
• Popular

EOS4 it is!

Stefan

Like
• Thanks a lot Stefan

Like
• 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.

Like

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

Like
• 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 )

Like

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

Like
• 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

Like

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

Like
• Thank you Stefan for your very helpful remarks

all the Best,

Like
• 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,

Like
• 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

Like
• 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

"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

Like

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

Like
• 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

Like
• 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

Like

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

Like
• 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

Like

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

Like
• 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,

Like