PhreeqcUsers Discussion Forum
Conceptual Models => Example input solutions => Topic started by: Mr.white on 25/03/26 08:54
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I have a question: if I define the length of each grid and the diffusion time in the transport settings, does that determine the diffusion speed of water? Then what is the diffusion coefficient defined in transport? I would like to understand the difference between diffusion speed and diffusion coefficient . Thank you.
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You'll have to look at some texts to get a better idea of the diffusion process. The flux of a constituent through an area depends on the gradient of the concentration and the diffusion coefficient. A larger gradient increases the flux, and a constituent with a larger diffusion coefficient, but the same gradient will have a larger flux.
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Okay, thank you very much. I just checked some textbooks and realized that I should be using advection to simulate the process of the water sample moving from the wellhead to the well bottom. I set up a 3000m long cell. Does that mean I can control the rate by changing the time?
SOLUTION 0
temp 25
pH 7
pe 4
redox pe
units ppm
density 1
Alkalinity 801 as HCO3
C(4) 639
Ca 12
Cl 11177
K 2407.2
Mg 7
Na 5616.8
S(6) 17
-water 1 # kg
SOLUTION 1
temp 70
pH 7
pe 4
redox pe
units ppm
density 1
Cl 0.0001
K 0.0001
Mg 0.0001
Na 0.0001
-water 0.1 # kg
TRANSPORT
-time_step 864000 # seconds = 10 days
-lengths 3000
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The advective velocity of water in TRANSPORT is the distance between two adjacent cell nodes divided by the time step.