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Transport of dilute species module

Posted Feb 9, 2015, 3:42 a.m. EST 6 Replies

Jayarama Krishna J V
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Hi,
Plz help me out to know how to enter nonlinear rate expressions bcz comsol is not taking powers like 0.5 i.e c*c2^0.5.
I kindly request anyone of them to give a reply soon.
Thanx a lot..
6 Replies Last Post Feb 9, 2015, 6:14 a.m. EST
Lasse Murtomäki
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Posted: 10 years ago Feb 9, 2015, 4:21 a.m. EST
Hi

Attached my solution to the problem; c is the variable. I used the flux condition

-k*C0*(c/C0)^a

where k is the heterogeneous rate constant (cm/s). You must use the scaling concentration C0 = 1 mol/L in the non-linear condition, because the units do not agree otherwise. Now, (c/C0)^a is dimensionless number. In order to make the flux in mol/(cm²·s), I multiply the expression again with C0, which makes the units correct. Basically, it is just question of dividing and multiplying with 1, but you must adjust the value of k to make the physical situation coincide with your experiments.

best regards
Lasse
Hi Attached my solution to the problem; c is the variable. I used the flux condition -k*C0*(c/C0)^a where k is the heterogeneous rate constant (cm/s). You must use the scaling concentration C0 = 1 mol/L in the non-linear condition, because the units do not agree otherwise. Now, (c/C0)^a is dimensionless number. In order to make the flux in mol/(cm²·s), I multiply the expression again with C0, which makes the units correct. Basically, it is just question of dividing and multiplying with 1, but you must adjust the value of k to make the physical situation coincide with your experiments. best regards Lasse

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Jayarama Krishna J V
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Posted: 10 years ago Feb 9, 2015, 5:12 a.m. EST
thanx sir but i am using 4.4 licensed version of comsol,so the .mph is not opening.When i tried to replace c2 by c2/C0 it is showing error telling dat C0 is unknown variable.
Regards
thanx sir but i am using 4.4 licensed version of comsol,so the .mph is not opening.When i tried to replace c2 by c2/C0 it is showing error telling dat C0 is unknown variable. Regards
Lasse Murtomäki
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Posted: 10 years ago Feb 9, 2015, 5:13 a.m. EST
You have to define C0, a and k in the global parameters list.
You have to define C0, a and k in the global parameters list.
Jayarama Krishna J V
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Posted: 10 years ago Feb 9, 2015, 5:43 a.m. EST
Respected Sir,
The following is the expression i wish to enter in the flux condition of transport of dilute species module.Plz let me know as where am i going wrong as comsol is showing error.
-0.476[mol^0.5/s*m^0.5]*(c[mol/m^3]*(c2[mol/m^3])^0.5)/(1+998*c[mol/m^3])
I will be extremely thankful to you
Regards
Respected Sir, The following is the expression i wish to enter in the flux condition of transport of dilute species module.Plz let me know as where am i going wrong as comsol is showing error. -0.476[mol^0.5/s*m^0.5]*(c[mol/m^3]*(c2[mol/m^3])^0.5)/(1+998*c[mol/m^3]) I will be extremely thankful to you Regards
Jayarama Krishna J V
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Posted: 10 years ago Feb 9, 2015, 5:52 a.m. EST
Thank you sir.I will definitely try by defining them in the global parameter list
Thank you sir.I will definitely try by defining them in the global parameter list
Lasse Murtomäki
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Posted: 10 years ago Feb 9, 2015, 6:14 a.m. EST
Hi

What is that 998 in the denominator? Water density in kg/m^3? Anyway, I would write

-k*c*(c2/C0)^a/(1+K*(c/C0))

k = 0.476[m/s] (or whatever you need)
C0 = 1[mol/l]
a = any number
K = 998 (no unit)

Now the flux has unit mol/(m²·s) since c has the unit mol/m^3.

br
Lasse
Hi What is that 998 in the denominator? Water density in kg/m^3? Anyway, I would write -k*c*(c2/C0)^a/(1+K*(c/C0)) k = 0.476[m/s] (or whatever you need) C0 = 1[mol/l] a = any number K = 998 (no unit) Now the flux has unit mol/(m²·s) since c has the unit mol/m^3. br Lasse

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