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Old   September 14, 2012, 03:06
Post Species transport and reaction
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Hi

I am trying to simulate a reaction between lithium and sulphur hexafluoride using the eddy dissipation model. I would like to know if I can input specific quantity of reactant..If I want to study the consumption of 5 kg of lithium in the reaction, is there any way where I can enter the amount of reactant used?
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Old   September 14, 2012, 13:12
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Originally Posted by snh View Post
Hi

I am trying to simulate a reaction between lithium and sulphur hexafluoride using the eddy dissipation model. I would like to know if I can input specific quantity of reactant..If I want to study the consumption of 5 kg of lithium in the reaction, is there any way where I can enter the amount of reactant used?
Hi,

Yes it's possible but in different manner.
First, you have to specify the rate of consumption (kg/s) and in a specified time, you can reach the consumed mass (kg).
To set a rate of consumption (kg/s), you can set source term of reactants in cells which are adjacent to the prescribed location where you want to have reaction near them. you can separate these cell and add the source terms in dimension of (kg/m3.s).

Bests,
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Old   September 15, 2012, 01:23
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Originally Posted by Amir View Post
Hi,

Yes it's possible but in different manner.
First, you have to specify the rate of consumption (kg/s) and in a specified time, you can reach the consumed mass (kg).
To set a rate of consumption (kg/s), you can set source term of reactants in cells which are adjacent to the prescribed location where you want to have reaction near them. you can separate these cell and add the source terms in dimension of (kg/m3.s).

Bests,
Hi Amir,
Thanks for the reply and your help is appreciated. I will try this out but I have no idea about the time required to consume the 5 kg of lithium (reactant). Also the reaction kinetics is not very well known. I only know that it is an instantaneous reaction. So what should I do in such case.
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Old   September 15, 2012, 04:07
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Originally Posted by snh View Post
Hi Amir,
Thanks for the reply and your help is appreciated. I will try this out but I have no idea about the time required to consume the 5 kg of lithium (reactant). Also the reaction kinetics is not very well known. I only know that it is an instantaneous reaction. So what should I do in such case.
Well, your chosen chemistry-turbulence model is appropriate. But regarding the amount of consumption, I think you can use a UDF, where you compute the amount of products in the whole domain via a volume integration and according to the stoichiometric reaction, you can stop the calculation when your constrain is justified.

Bests,
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Old   September 16, 2012, 04:50
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Quote:
Originally Posted by snh View Post
Hi

I am trying to simulate a reaction between lithium and sulphur hexafluoride using the eddy dissipation model. I would like to know if I can input specific quantity of reactant..If I want to study the consumption of 5 kg of lithium in the reaction, is there any way where I can enter the amount of reactant used?
Hello,
At first you should have the reaction rate. Then you can use DEFINE_NET_REACTION_RATE macro for implementing the reaction rate. Like this:

DEFINE_NET_REACTION_RATE(user_net_reaction_rate,c, t,particle,pressure,temp,yi,rr,jac)
{
int i;
for(i=0;i<n_spe;i++)
rr[i] = 1./(real)n_spe - yi[i];
}
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Old   September 17, 2012, 03:25
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Originally Posted by Amir View Post
Well, your chosen chemistry-turbulence model is appropriate. But regarding the amount of consumption, I think you can use a UDF, where you compute the amount of products in the whole domain via a volume integration and according to the stoichiometric reaction, you can stop the calculation when your constrain is justified.

Bests,
Hi Amir,

I have one more question. The lithium that is used in the reaction is already present in the reactor in molten form and its amount is 5 kg & the oxidizer i.e. sulphur hexafluoride is injected through a nozzle. So in this case can I use the source term to specify the amount of lithium since the amount of lithium present in the reactor is not increasing with time and is decreasing as the reaction proceeds.

Thank You.
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Old   September 17, 2012, 04:38
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Originally Posted by eng_s_sadeghi View Post
Hello,
At first you should have the reaction rate. Then you can use DEFINE_NET_REACTION_RATE macro for implementing the reaction rate. Like this:

DEFINE_NET_REACTION_RATE(user_net_reaction_rate,c, t,particle,pressure,temp,yi,rr,jac)
{
int i;
for(i=0;i<n_spe;i++)
rr[i] = 1./(real)n_spe - yi[i];
}
Hi,

Thank you for joining in. I will implement the reaction rate as mentioned by you. I would like to know if there is any way by which I can mention that 5kg of lithium (reactant) is already present in the reactor. Since I am new to fluent, I am facing problem of modeling my problem statement in a correct way in fluent.

Thank you.
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Old   September 17, 2012, 06:01
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Quote:
Originally Posted by snh View Post
Hi Amir,

I have one more question. The lithium that is used in the reaction is already present in the reactor in molten form and its amount is 5 kg & the oxidizer i.e. sulphur hexafluoride is injected through a nozzle. So in this case can I use the source term to specify the amount of lithium since the amount of lithium present in the reactor is not increasing with time and is decreasing as the reaction proceeds.

Thank You.
Hi,

I think your concern is about pyrolysis of the lithium which doesn't have any relation to the rate of reaction; you've used a proper turbulence-chemistry model.
You have to know that FLUENT is not a technical software in reaction simulation so you have to model few parameters such as rate of pyrolyzation.
i.e., you can define a proper relation as a source term to release desired amount of reactant and let FLUENT find the rate of reaction according to the eddy dissipation model. (If you have a hydrocarbon fuel I strongly recommend you to use FDS instead of FLUENT)

Bests,
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Old   September 17, 2012, 06:13
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Hi,

Fluent is highly powerful software that can be used for solving all finite volume problems. It you see it doesn't have predefined modules for your problem, you can use it just as a high speed solver core, as I have done in my master project (solid fuel combustion in a packed bed of porous materials).

In this project, I have used fluent just as a solver and have written more than 1400 lines of complex User Defined Functions for implementing solid fuel combustion, limestone decomposition, moisture evaporation and condensation and other parameters that required for modeling this process.

I believe in Ansys Fluent and I am sure all Finite Volume problems can be solved by UDF programming in it.
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Old   September 17, 2012, 06:34
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Originally Posted by eng_s_sadeghi View Post
Hi,
I believe in Ansys Fluent and I am sure all Finite Volume problems can be solved by UDF programming in it.
You're kidding!
Have you ever seen alternative open source softwares such as openFOAM?!!
FLUENT is very restrictive in comparison to such softwares. e.g., can you implement you own pressure-velocity coupling method or discretization scheme?!
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Old   September 17, 2012, 06:50
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You're kidding!
Have you ever seen alternative open source softwares such as openFOAM?!!
FLUENT is very restrictive in comparison to such softwares. e.g., can you implement you own pressure-velocity coupling method or discretization scheme?!
As I said, as a solver core. Do you understand?
I mean if there would not be any need to change the discretization, as in most problems there is no need of changing the solving method. The only problem would be just to add equations.
How much time does it take to change OpenFOAM solver core? I am not so crazy to do that...
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Old   September 17, 2012, 06:55
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You're kidding!
Have you ever seen alternative open source softwares such as openFOAM?!!
FLUENT is very restrictive in comparison to such softwares. e.g., can you implement you own pressure-velocity coupling method or discretization scheme?!
I don't like discretizing problem. They are not duty of a mechanical engineering. Mathematicians should deal with it not a mechanical engineer. I hate it.
What is your experience? Discretizing, haha. You will not get in touch with the phenomena with just work with them.
I hope you understand what I mean.
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Old   September 17, 2012, 09:24
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As I said, as a solver core. Do you understand?
It seems that you don't exactly know what the solver core is! The discretization schemes are not categorized as a part of solver core, they are additional compiled libraries which attached to the solver core. ("dll" files in windows and "so" files in linux)
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I mean if there would not be any need to change the discretization, as in most problems there is no need of changing the solving method. The only problem would be just to add equations.
Not at all! you can severely save time if you use optimized code in all of its aspects.
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How much time does it take to change OpenFOAM solver core? I am not so crazy to do that...
I'm surprising! It depends on your capabilities but if you think so, it's better for you just to use FLUENT.
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I don't like discretizing problem. They are not duty of a mechanical engineering. Mathematicians should deal with it not a mechanical engineer. I hate it.
If you really think so, I'm very sorry for you.
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What is your experience? Discretizing, haha. You will not get in touch with the phenomena with just work with them.
No this is not my experience. My field is viscoelastic fluids; lost capability of FLUENT!
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Old   September 17, 2012, 09:42
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OK. I don't know CFD. Goodluck.
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