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Help required Plz

Posted Mar 14, 2011, 12:44 a.m. EDT Heat Transfer & Phase Change, Chemical Reaction Engineering, Geometry, Materials, Modeling Tools & Definitions, Parameters, Variables, & Functions, Results & Visualization, Studies & Solvers Version 4.1 11 Replies

Faysal Khan
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Dear Experts,


I am having trouble defining variable under model builder and can not move further

this is how i defined my variables under Model builder>Mod1

rate rate_in_cat*W_cat
rate_in_cat num/deno
num k0*(c_C2H6O)*exp((-E)/(R_const*T_reaction))
deno (1+K_A*c_C2H6O)^2

now, c_C2H6O is a dependent variable in <chds> physics

my model is not solving for concentration profile for C2H6O

Please can anyone tell me where i am having trouble?

regards
--
Faysal
11 Replies Last Post Mar 14, 2011, 7:47 p.m. EDT
Faysal Khan
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Posted: 1 decade ago Mar 14, 2011, 12:45 a.m. EDT

Please find attached my model
--
Faysal
Please find attached my model -- Faysal
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 1 decade ago Mar 14, 2011, 2:21 a.m. EDT
Hi

First you should update to latest patch, see the main COMSOL site

You have your Heat Sorce 1 that is not defined on any domain (I agree with only 1 domain COMSOL could default to it, but it's not so, the user is supposed to define each step, I'm also in preference for that, even if it takes some time, there are enough buttons inside COMSOL)

There seem to be the main issue with:

"chds.z_c_C2H6O" is this a typo ? or was it "chds.c_C2H6Oz" you ment ?
it's difficult for me (without studying your model in further detials and write out all equations to analyse much further

the error in the dependent variable node "mod1_c_C2H6O" not to confuse with variable mod1.c_C2H6O the notation in the error message is also confusing I find, is also linked to that previous error

When referring to dependent variables in other physics, the current version of COMSOL gives often false unit or variable error messages, you must load the initial conditions to clear them and fully verify your model

At least by changing the location of the "z" in the variable above I can solve, even if it fails with a singularity (max iteration), not converging. This makes me believe your initial conditions are too far from the solution, and improving this could probably help

The results indicate that the C_C2H60 is saturating, sure you reaction rates are correct, or was my "z" correction wrong ;)


--
Good luck
Ivar
Hi First you should update to latest patch, see the main COMSOL site You have your Heat Sorce 1 that is not defined on any domain (I agree with only 1 domain COMSOL could default to it, but it's not so, the user is supposed to define each step, I'm also in preference for that, even if it takes some time, there are enough buttons inside COMSOL) There seem to be the main issue with: "chds.z_c_C2H6O" is this a typo ? or was it "chds.c_C2H6Oz" you ment ? it's difficult for me (without studying your model in further detials and write out all equations to analyse much further the error in the dependent variable node "mod1_c_C2H6O" not to confuse with variable mod1.c_C2H6O the notation in the error message is also confusing I find, is also linked to that previous error When referring to dependent variables in other physics, the current version of COMSOL gives often false unit or variable error messages, you must load the initial conditions to clear them and fully verify your model At least by changing the location of the "z" in the variable above I can solve, even if it fails with a singularity (max iteration), not converging. This makes me believe your initial conditions are too far from the solution, and improving this could probably help The results indicate that the C_C2H60 is saturating, sure you reaction rates are correct, or was my "z" correction wrong ;) -- Good luck Ivar
Faysal Khan
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Posted: 1 decade ago Mar 14, 2011, 4:05 a.m. EDT
Dear Iver


First of many many thanks for your reply. Scrating my head here ... ;)

Please i would highly appreciate if you could go through my reply and give me some guideline to proceed.
** i also have attached a modified COMSOL solution to my problem, but its not working ... :(



Hi

First you should update to latest patch, see the main COMSOL site

**** I can not update to latest patch, though i tried to do it in C:\COMSOL41 folder, it says "cannot create output file: C:\COMSOL41\lib\win32\ipv4\flnutil.dll" *******


You have your Heat Sorce 1 that is not defined on any domain (I agree with only 1 domain COMSOL could default to it, but it's not so, the user is supposed to define each step, I'm also in preference for that, even if it takes some time, there are enough buttons inside COMSOL) *****==> sorry, this was my mistake, corrected it, but still not getting any profile for concentration of C2H6O *******

There seem to be the main issue with:

"chds.z_c_C2H6O" is this a typo ? or was it "chds.c_C2H6Oz" you ment ? ***** i was removed this ****
it's difficult for me (without studying your model in further detials and write out all equations to analyse much further

the error in the dependent variable node "mod1_c_C2H6O" not to confuse with variable mod1.c_C2H6O the notation in the error message is also confusing I find, is also linked to that previous error

**** actually, i was wondering why comsol is not changing concentration of C2H6O (c_C2H6O) while solving along z axis, because it has rate expression defined in variable ******

When referring to dependent variables in other physics, the current version of COMSOL gives often false unit or variable error messages, you must load the initial conditions to clear them and fully verify your model

At least by changing the location of the "z" in the variable above I can solve, even if it fails with a singularity (max iteration), not converging. This makes me believe your initial conditions are too far from the solution, and improving this could probably help

The results indicate that the C_C2H60 is saturating, sure you reaction rates are correct, or was my "z" correction wrong ;)

**** my model is very simple , i have a rate expression, in the inlet i have inlet concentration of C2H6O and H2O, along the reactor bed, C2H6O and H2O reacting to produce CO2 and H2, it is and exothermic reaction, i brought that heat flux because there is a furnace which will supply heat if bed temperature falls!!, this model is from a journal article, trying to reproduce there results in COMSOL, they also have done COMSOL modeling of this problem, "Experimental studies and comprehensive reactor modeling of hydrogen production by ........" by Ahmed Aboudheir, Internation journal of Hydrogen Energy 31 (2006) 752-761 ************


--
Good luck
Ivar



Many many thanks

Regards

--
Faysal
Dear Iver First of many many thanks for your reply. Scrating my head here ... ;) Please i would highly appreciate if you could go through my reply and give me some guideline to proceed. ** i also have attached a modified COMSOL solution to my problem, but its not working ... :( [QUOTE] Hi First you should update to latest patch, see the main COMSOL site **** I can not update to latest patch, though i tried to do it in C:\COMSOL41 folder, it says "cannot create output file: C:\COMSOL41\lib\win32\ipv4\flnutil.dll" ******* You have your Heat Sorce 1 that is not defined on any domain (I agree with only 1 domain COMSOL could default to it, but it's not so, the user is supposed to define each step, I'm also in preference for that, even if it takes some time, there are enough buttons inside COMSOL) *****==> sorry, this was my mistake, corrected it, but still not getting any profile for concentration of C2H6O ******* There seem to be the main issue with: "chds.z_c_C2H6O" is this a typo ? or was it "chds.c_C2H6Oz" you ment ? ***** i was removed this **** it's difficult for me (without studying your model in further detials and write out all equations to analyse much further the error in the dependent variable node "mod1_c_C2H6O" not to confuse with variable mod1.c_C2H6O the notation in the error message is also confusing I find, is also linked to that previous error **** actually, i was wondering why comsol is not changing concentration of C2H6O (c_C2H6O) while solving along z axis, because it has rate expression defined in variable ****** When referring to dependent variables in other physics, the current version of COMSOL gives often false unit or variable error messages, you must load the initial conditions to clear them and fully verify your model At least by changing the location of the "z" in the variable above I can solve, even if it fails with a singularity (max iteration), not converging. This makes me believe your initial conditions are too far from the solution, and improving this could probably help The results indicate that the C_C2H60 is saturating, sure you reaction rates are correct, or was my "z" correction wrong ;) **** my model is very simple , i have a rate expression, in the inlet i have inlet concentration of C2H6O and H2O, along the reactor bed, C2H6O and H2O reacting to produce CO2 and H2, it is and exothermic reaction, i brought that heat flux because there is a furnace which will supply heat if bed temperature falls!!, this model is from a journal article, trying to reproduce there results in COMSOL, they also have done COMSOL modeling of this problem, "Experimental studies and comprehensive reactor modeling of hydrogen production by ........" by Ahmed Aboudheir, Internation journal of Hydrogen Energy 31 (2006) 752-761 ************ -- Good luck Ivar [/QUOTE] Many many thanks Regards -- Faysal
Faysal Khan
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Posted: 1 decade ago Mar 14, 2011, 4:05 a.m. EDT
Dear Iver


First of many many thanks for your reply. Scrating my head here ... ;)

Please i would highly appreciate if you could go through my reply and give me some guideline to proceed.
** i also have attached a modified COMSOL solution to my problem, but its not working ... :(



Hi

First you should update to latest patch, see the main COMSOL site

**** I can not update to latest patch, though i tried to do it in C:\COMSOL41 folder, it says "cannot create output file: C:\COMSOL41\lib\win32\ipv4\flnutil.dll" *******


You have your Heat Sorce 1 that is not defined on any domain (I agree with only 1 domain COMSOL could default to it, but it's not so, the user is supposed to define each step, I'm also in preference for that, even if it takes some time, there are enough buttons inside COMSOL) *****==> sorry, this was my mistake, corrected it, but still not getting any profile for concentration of C2H6O *******

There seem to be the main issue with:

"chds.z_c_C2H6O" is this a typo ? or was it "chds.c_C2H6Oz" you ment ? ***** i was removed this ****
it's difficult for me (without studying your model in further detials and write out all equations to analyse much further

the error in the dependent variable node "mod1_c_C2H6O" not to confuse with variable mod1.c_C2H6O the notation in the error message is also confusing I find, is also linked to that previous error

**** actually, i was wondering why comsol is not changing concentration of C2H6O (c_C2H6O) while solving along z axis, because it has rate expression defined in variable ******

When referring to dependent variables in other physics, the current version of COMSOL gives often false unit or variable error messages, you must load the initial conditions to clear them and fully verify your model

At least by changing the location of the "z" in the variable above I can solve, even if it fails with a singularity (max iteration), not converging. This makes me believe your initial conditions are too far from the solution, and improving this could probably help

The results indicate that the C_C2H60 is saturating, sure you reaction rates are correct, or was my "z" correction wrong ;)

**** my model is very simple , i have a rate expression, in the inlet i have inlet concentration of C2H6O and H2O, along the reactor bed, C2H6O and H2O reacting to produce CO2 and H2, it is and exothermic reaction, i brought that heat flux because there is a furnace which will supply heat if bed temperature falls!!, this model is from a journal article, trying to reproduce there results in COMSOL, they also have done COMSOL modeling of this problem, "Experimental studies and comprehensive reactor modeling of hydrogen production by ........" by Ahmed Aboudheir, Internation journal of Hydrogen Energy 31 (2006) 752-761 ************


--
Good luck
Ivar



Many many thanks

Regards

--
Faysal
Dear Iver First of many many thanks for your reply. Scrating my head here ... ;) Please i would highly appreciate if you could go through my reply and give me some guideline to proceed. ** i also have attached a modified COMSOL solution to my problem, but its not working ... :( [QUOTE] Hi First you should update to latest patch, see the main COMSOL site **** I can not update to latest patch, though i tried to do it in C:\COMSOL41 folder, it says "cannot create output file: C:\COMSOL41\lib\win32\ipv4\flnutil.dll" ******* You have your Heat Sorce 1 that is not defined on any domain (I agree with only 1 domain COMSOL could default to it, but it's not so, the user is supposed to define each step, I'm also in preference for that, even if it takes some time, there are enough buttons inside COMSOL) *****==> sorry, this was my mistake, corrected it, but still not getting any profile for concentration of C2H6O ******* There seem to be the main issue with: "chds.z_c_C2H6O" is this a typo ? or was it "chds.c_C2H6Oz" you ment ? ***** i was removed this **** it's difficult for me (without studying your model in further detials and write out all equations to analyse much further the error in the dependent variable node "mod1_c_C2H6O" not to confuse with variable mod1.c_C2H6O the notation in the error message is also confusing I find, is also linked to that previous error **** actually, i was wondering why comsol is not changing concentration of C2H6O (c_C2H6O) while solving along z axis, because it has rate expression defined in variable ****** When referring to dependent variables in other physics, the current version of COMSOL gives often false unit or variable error messages, you must load the initial conditions to clear them and fully verify your model At least by changing the location of the "z" in the variable above I can solve, even if it fails with a singularity (max iteration), not converging. This makes me believe your initial conditions are too far from the solution, and improving this could probably help The results indicate that the C_C2H60 is saturating, sure you reaction rates are correct, or was my "z" correction wrong ;) **** my model is very simple , i have a rate expression, in the inlet i have inlet concentration of C2H6O and H2O, along the reactor bed, C2H6O and H2O reacting to produce CO2 and H2, it is and exothermic reaction, i brought that heat flux because there is a furnace which will supply heat if bed temperature falls!!, this model is from a journal article, trying to reproduce there results in COMSOL, they also have done COMSOL modeling of this problem, "Experimental studies and comprehensive reactor modeling of hydrogen production by ........" by Ahmed Aboudheir, Internation journal of Hydrogen Energy 31 (2006) 752-761 ************ -- Good luck Ivar [/QUOTE] Many many thanks Regards -- Faysal
Mayur
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Posted: 1 decade ago Mar 14, 2011, 3:24 p.m. EDT
You have to solve for the flow as well..I have modified your file..have look..now there is a concentration profile of C2H6O..
cheers
Mayur
You have to solve for the flow as well..I have modified your file..have look..now there is a concentration profile of C2H6O.. cheers Mayur
Mayur
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Posted: 1 decade ago Mar 14, 2011, 4:06 p.m. EDT
there is one mistake in the file..replace u with w in convection-diffusion physics for z-velocity...
cheers
there is one mistake in the file..replace u with w in convection-diffusion physics for z-velocity... cheers
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 1 decade ago Mar 14, 2011, 4:40 p.m. EDT
Hi

I did not have any issues with the update, are you sure 1) all COMSOL executables were stopped ? and 2) that you have the write rights on that directory ? Sometimes it's worth to reboot fresh before doing an update (if you have a PC ;)

Then "chds.z_c_C2H6O" could perhaps have been simply "c_C2H6O" ? This could explain why it is not changing (adding the z is the spatial z derivative)

I'll take a quick look at your model:

Have you noticed that you get up to 27.5 atm pressure at the inlet ? I do not know if that is OK. Anyhow you used 1atm in the porous media gauge pressure ( for initial conditions and for the outlet, and then you add this to the 1atm reference pressure in the HT module (this might be 1atm more than expected by addition).

you can also see evolution either try a transient, or just turn on the plotting while solving in the "output" section of the fully coupled solver node

--
Good luck
Ivar
Hi I did not have any issues with the update, are you sure 1) all COMSOL executables were stopped ? and 2) that you have the write rights on that directory ? Sometimes it's worth to reboot fresh before doing an update (if you have a PC ;) Then "chds.z_c_C2H6O" could perhaps have been simply "c_C2H6O" ? This could explain why it is not changing (adding the z is the spatial z derivative) I'll take a quick look at your model: Have you noticed that you get up to 27.5 atm pressure at the inlet ? I do not know if that is OK. Anyhow you used 1atm in the porous media gauge pressure ( for initial conditions and for the outlet, and then you add this to the 1atm reference pressure in the HT module (this might be 1atm more than expected by addition). you can also see evolution either try a transient, or just turn on the plotting while solving in the "output" section of the fully coupled solver node -- Good luck Ivar
Faysal Khan
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Posted: 1 decade ago Mar 14, 2011, 6:56 p.m. EDT

You have to solve for the flow as well..I have modified your file..have look..now there is a concentration profile of C2H6O..
cheers
Mayur



Dear Mayur,

Thank you so much for your effort and it really means a lot to me.

I am very sorry to let you know that i can not open your file cause i do not have the license for Batteries and Fuel cell mode ........
Now,
I am trying to add a fluid flow physics to my model, but i am afraid that my model is an isobaric operation and isothermal too, all through the reactor there should not be any pressure drop , so i am a little confused at this moment ,,,,,,,,,,,,, can you give me any suggestion in this regards.

by the way i have this model solved too some way (not sure if that is correct, but got close to article results) in COMSOL 3.5 but as i do not have the license for 3.5 anymore so i can not open it there, just trying to learn COMSOL 4.1 from the scratch , to be mention, i was a beginner on COMSOL 3.5 too. ....... :( ....

i have attached the model of 3.5, if anyhow you could help me to convert it ...
Regards
--
Faysal
[QUOTE] You have to solve for the flow as well..I have modified your file..have look..now there is a concentration profile of C2H6O.. cheers Mayur [/QUOTE] Dear Mayur, Thank you so much for your effort and it really means a lot to me. I am very sorry to let you know that i can not open your file cause i do not have the license for Batteries and Fuel cell mode ........ Now, I am trying to add a fluid flow physics to my model, but i am afraid that my model is an isobaric operation and isothermal too, all through the reactor there should not be any pressure drop , so i am a little confused at this moment ,,,,,,,,,,,,, can you give me any suggestion in this regards. by the way i have this model solved too some way (not sure if that is correct, but got close to article results) in COMSOL 3.5 but as i do not have the license for 3.5 anymore so i can not open it there, just trying to learn COMSOL 4.1 from the scratch , to be mention, i was a beginner on COMSOL 3.5 too. ....... :( .... i have attached the model of 3.5, if anyhow you could help me to convert it ... Regards -- Faysal
Mayur
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Posted: 1 decade ago Mar 14, 2011, 7:30 p.m. EDT
You do not need batteries and fuel cell physics for this. I can see that your model is packed bed and it is a reforming of C2H6O which is endothermic reaction, i.e. there must be a pressure drop and you can maintain isothermal condition by implementing external heat source.
You do not need batteries and fuel cell physics for this. I can see that your model is packed bed and it is a reforming of C2H6O which is endothermic reaction, i.e. there must be a pressure drop and you can maintain isothermal condition by implementing external heat source.
Faysal Khan
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Posted: 1 decade ago Mar 14, 2011, 7:35 p.m. EDT

You do not need batteries and fuel cell physics for this. I can see that your model is packed bed and it is a reforming of C2H6O which is endothermic reaction, i.e. there must be a pressure drop and you can maintain isothermal condition by implementing external heat source.



Dear Mayur,

Thanks again for your reply. Really grateful.

Please check the JPEG picture. This is what i am having trouble opening your model in my PC.


Regards

--
Faysal
[QUOTE] You do not need batteries and fuel cell physics for this. I can see that your model is packed bed and it is a reforming of C2H6O which is endothermic reaction, i.e. there must be a pressure drop and you can maintain isothermal condition by implementing external heat source. [/QUOTE] Dear Mayur, Thanks again for your reply. Really grateful. Please check the JPEG picture. This is what i am having trouble opening your model in my PC. Regards -- Faysal

Attachments:

Mayur
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Posted: 1 decade ago Mar 14, 2011, 7:47 p.m. EDT
Hi,
I don't know whats the problem is, I have used the physics under chemical engineering, fluid flow and heat transfer...so there must be something else! may be you should contact the support related to this.
good luck
Mayur
Hi, I don't know whats the problem is, I have used the physics under chemical engineering, fluid flow and heat transfer...so there must be something else! may be you should contact the support related to this. good luck Mayur

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