Horizontal flow of solute in a flow cell using Hydrus 2D

A discussion forum for users of the new HYDRUS 2D/3D. HYDRUS is a software package for simulating water, heat and solute movement in two- and three-dimensional variably saturated media. Happy Posting!
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rmohamed
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Joined: Tue May 11, 2021 3:32 pm
Location: USA

Horizontal flow of solute in a flow cell using Hydrus 2D

Post by rmohamed » Tue May 11, 2021 4:25 pm

Hello Sir,

I am trying to simulate a transient horizontal solute transport in a flow cell (40 cm X 12 cm X 2.5. cm) packed with saturated sand in the lab. I set a boundary condition in the inlet as variable flux and in the outlet as atmospheric. I set initial condition in the water content as Qs (because the sand was saturated) and in concentration as zero. For some reason the model does not see the solute and I get zero in the concentration output. Any suggestions?

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Jirka
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Location: Riverside, CA

Re: Horizontal flow of solute in a flow cell using Hydrus 2D

Post by Jirka » Tue May 11, 2021 5:15 pm

You cannot have solute outflow at the atmospheric BC. Atmospheric BC assumes that outflow is due to evaporation, and solutes do not leave the soil profile with evaporation (they stay behind in the soil). J.

rmohamed
Posts: 8
Joined: Tue May 11, 2021 3:32 pm
Location: USA

Re: Horizontal flow of solute in a flow cell using Hydrus 2D

Post by rmohamed » Thu May 27, 2021 4:11 pm

Hi Sir,

I am still not able to see a solute breakthrough curve in the output. Given that the solute was injected horizontally in the inlet of a saturated flowcell and was collected in the outlet: I set water boundary condition in the inlet and outlet as 'Const. Flux' and assigned a value of 0.101 cm/min in the inlet and -0.101 cm/min in the outlet. I set solute transport boundary condition as 'First-Type'. I set solute concentration as a variable boundary condition in 'cValue2' for the first 320 minutes (Pulse duration). I set initial boundary condition for water content as 'Q's (because the flowcell was saturated) and set initial boundary condition for concentration as 'zero'. I am not certain why I am not seeing a breakthrough curve in the output. Thanks.

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Jirka
Posts: 5268
Joined: Sat Mar 16, 2002 3:47 pm
Location: USA
Location: Riverside, CA

Re: Horizontal flow of solute in a flow cell using Hydrus 2D

Post by Jirka » Thu May 27, 2021 8:13 pm

You will need to post your project, otherwise we cannot say what is wrong and what is right. J.

rmohamed
Posts: 8
Joined: Tue May 11, 2021 3:32 pm
Location: USA

Re: Horizontal flow of solute in a flow cell using Hydrus 2D

Post by rmohamed » Fri May 28, 2021 2:57 am

Yes, absolutely. The project is attached. Thank you.
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Jirka
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Location: Riverside, CA

Re: Horizontal flow of solute in a flow cell using Hydrus 2D

Post by Jirka » Fri May 28, 2021 3:54 am

Here it is. You specified zero concentration at the inflow. For constant flux BCs, the boundary concentrations are specified in the vector “Boundary Conditions” in the “Reaction Parameters for Solute 1” window. J.
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rmohamed
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Location: USA

Re: Horizontal flow of solute in a flow cell using Hydrus 2D

Post by rmohamed » Sat May 29, 2021 12:39 pm

Awesome! Thank you!

rmohamed
Posts: 8
Joined: Tue May 11, 2021 3:32 pm
Location: USA

Re: Horizontal flow of solute in a flow cell using Hydrus 2D

Post by rmohamed » Tue Jun 15, 2021 7:35 pm

Hi Sir,

I get output concentrations in a different unit than the input concentration boundary condition. I used a concentration boundary condition as 0.00025 gm/cm^3 and yet get an output concentration larger than the input concentration (the output concentration ranged between 0 and 1.2). I also used soil bulk density as 1.61 gm/cm^3 unit. Any idea what the output concentration unit is and why it is different than the concentration boundary condition? Thanks.
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Jirka
Posts: 5268
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Location: USA
Location: Riverside, CA

Re: Horizontal flow of solute in a flow cell using Hydrus 2D

Post by Jirka » Wed Jun 16, 2021 7:31 pm

Your input concentration value is equal to 1. The output concentration values are also up to one. Note that for constant head/flux boundary flow conditions, solute transport BCs are given in the “Boundary Conditions” vector in the “Reaction Parameters” window. If you want to use the concentration value of 0.00025 (which you give in the Variable BC window, and which is not used since you do not have any time-variable inflow conditions), you need to copy this value there. J.

rmohamed
Posts: 8
Joined: Tue May 11, 2021 3:32 pm
Location: USA

Re: Horizontal flow of solute in a flow cell using Hydrus 2D

Post by rmohamed » Fri Jun 18, 2021 6:31 pm

That worked. Thank you!

rmohamed
Posts: 8
Joined: Tue May 11, 2021 3:32 pm
Location: USA

Re: Horizontal flow of solute in a flow cell using Hydrus 2D

Post by rmohamed » Tue Jun 22, 2021 6:24 pm

Hi Sir,

I added another type of soil in the middle of the domain and kept all initial and boundary conditions similar. The model does not converge for some reason.

Thank you
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Jirka
Posts: 5268
Joined: Sat Mar 16, 2002 3:47 pm
Location: USA
Location: Riverside, CA

Re: Horizontal flow of solute in a flow cell using Hydrus 2D

Post by Jirka » Tue Jun 22, 2021 7:03 pm

You probably want to adjust the initial condition as well. Since you specify the initial water content equal to 0.33, the external material is saturated and internal material is unsaturated. If you specify the initial condition in terms of the pressure head you can have the entire profile saturated and the program will converge just fine.

Note: I cannot help you with every little change in your project. You do need to be able to resolve some problems by yourself.

J.

rmohamed
Posts: 8
Joined: Tue May 11, 2021 3:32 pm
Location: USA

Re: Horizontal flow of solute in a flow cell using Hydrus 2D

Post by rmohamed » Wed Jun 23, 2021 8:35 pm

Thank you for your feed back. It worked after setting the initial condition to pressure head. Much appreciated.

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