Inpact of water content on heat transport

A discussion forum for Hydrus-1D users.
Post Reply
Michel
Posts: 3
Joined: Tue May 05, 2020 2:13 pm
Location: Austria

Inpact of water content on heat transport

Post by Michel » Tue May 05, 2020 2:47 pm

Hello everyone!

I am currently writing my master thesis, where we are investigating the inpact of high temperatures at the atmosphere in the summer on the temperature changes in water distribution System. With hydrus1D i am modelling the temperature change from the top surface layer into the underground. The main process is therefore the HEAT TRANSPORT.
The model consists of 4 layers for the road construction and a soil layer and i have the thermal properties of all of them and also the temperature at the Surface.
For the U.BC i use "Atmospheric BC with Surface runoff" and the L.BC "free Drainage", initial condition is pressure heads.

I want to analyze the inpact of the water Content when i Change it from 0% in 5%steps into full Saturation. At the top layers (pavement) i have no water Content at all, so the Change is only in the soil layer.
My Problem now is that there is no change of the soil temperature when i Change the watercontent at all, which seems kind of unrealistic to me :?:
Any advises what could be wrong? Do i need water transport (main process) in order to have a realistic model with hydraulic conductivity?

Any help is highly appreciatet (i am new to hydrus)!

Thanks, Michel

Jirka
Posts: 4922
Joined: Sat Mar 16, 2002 3:47 pm
Location: USA
Location: Riverside, CA

Re: Inpact of water content on heat transport

Post by Jirka » Tue May 05, 2020 6:11 pm

The effect of water content on heat transport is often not very large since water content affects both thermal capacity and thermal conductivity (both increasing with water content). If you express the heat transport equation in terms of thermal diffusivity (ratio of thermal capacity and heat capacity), you can easily see you can have two very different water contents for which thermal diffusivity is the same, and so is the heat transport. J.
ThermalProp.png
ThermalProp.png (17.82 KiB) Viewed 483 times

Michel
Posts: 3
Joined: Tue May 05, 2020 2:13 pm
Location: Austria

Re: Inpact of water content on heat transport

Post by Michel » Wed May 06, 2020 7:14 am

Thanks for your reply, jirka!

I was also using the equations from Chung&Horton as used in Hydrus and came to the same conclusion, that the inpact of the water content isn't to big on the thermal diffusivity. However i was thinking that the heat transport trough to convection would be affected more?

And i got one more question (just for understanding), it might be just a misunderstanding:
Is the residual water Content Qr defining the actual water Content, that is in the soil during the Simulation?

Greetings, Michel

Jirka
Posts: 4922
Joined: Sat Mar 16, 2002 3:47 pm
Location: USA
Location: Riverside, CA

Re: Inpact of water content on heat transport

Post by Jirka » Wed May 06, 2020 5:43 pm

Conduction usually dominates heat transport unless the water fluxes are quite large (at least one meter per day). See:
Hopmans, J. W., J. Šimůnek, and K. L. Bristow, Indirect estimation of soil thermal properties and water flux using heat pulse probe measurements: Geometry and dispersion effects, Water Resources Research, 38(1), 10.1029/2000WR000071, 7.1-7.14, 2002.

No, the residual water content certainly does not define the actual water content in the soil during the simulation.

J.

Jirka
Posts: 4922
Joined: Sat Mar 16, 2002 3:47 pm
Location: USA
Location: Riverside, CA

Re: Inpact of water content on heat transport

Post by Jirka » Wed May 06, 2020 5:43 pm

Conduction usually dominates heat transport unless the water fluxes are quite large (at least one meter per day). See:
Hopmans, J. W., J. Šimůnek, and K. L. Bristow, Indirect estimation of soil thermal properties and water flux using heat pulse probe measurements: Geometry and dispersion effects, Water Resources Research, 38(1), 10.1029/2000WR000071, 7.1-7.14, 2002.

No, the residual water content certainly does not define the actual water content in the soil during the simulation.

J.

Michel
Posts: 3
Joined: Tue May 05, 2020 2:13 pm
Location: Austria

Re: Inpact of water content on heat transport

Post by Michel » Thu May 21, 2020 7:33 pm

Dear Jirka,

i understand now that i had some misunderstanding with the residual water content, but i still got some understanding Problems…

So the actual water content is calculated with the van Genuchten function, where i need the Soil Hydraulic Parameters and the pressure head. The Hydraulic Parameters depend on my chosen soil and stay the same. But im still not quite sure how and where i Change the actual water content (through to the pressure head) that it stays the same for the whole simulation. Up to now i thought the only way to Change the water content is with the Initial Condition (i chose IC pressure heads) and Change the initial condition in the graphical Editor for different Outputs.

But the Observation Points - plot Always says i have a water content of 0,38 no matter what initial condition of the pressure head i choose. I couldnt figure it out with the Manual, if there is another way to Change the water content.

thanks, Michel

Jirka
Posts: 4922
Joined: Sat Mar 16, 2002 3:47 pm
Location: USA
Location: Riverside, CA

Re: Inpact of water content on heat transport

Post by Jirka » Thu May 21, 2020 9:10 pm

It seems that you have no idea what Hydrus actually does. Perhaps, you should first do some tutorials before you start asking further questions.

CSIRO Tutorial eBook: https://www.pc-progress.com/Downloads/P ... 0_2018.pdf

Rassam, D., J. Šimůnek, D. Mallants, and M. Th. van Genuchten, The HYDRUS-1D Software Package for Simulating the Movement of Water, Heat, and Multiple Solutes in Variably Saturated Media: Tutorial, Version 1.00, CSIRO Land and Water, Adelaide, Australia, 183 pp., ISBN 978-1-4863-1001-2, 2018. Appendices I, II, and III.

J.

Post Reply