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Transport of dilute species module

Posted 9 feb 2015, 03:42 GMT-5 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 9 feb 2015, 06:14 GMT-5
Lasse Murtomäki
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Posted: 1 decade ago 9 feb 2015, 04:21 GMT-5
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: 1 decade ago 9 feb 2015, 05:12 GMT-5
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: 1 decade ago 9 feb 2015, 05:13 GMT-5
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: 1 decade ago 9 feb 2015, 05:43 GMT-5
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: 1 decade ago 9 feb 2015, 05:52 GMT-5
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: 1 decade ago 9 feb 2015, 06:14 GMT-5
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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