chemical reaction

Sara28 · July 30, 2015, 01:40

Hello together,

is there any way to do chemical reactions without knowing the reactionmechanism? Just to see where the fluid flows and where the products after the reaction occur?

Thanks for your advices!

Sara

CeesH · July 30, 2015, 02:40

Hi,

If you use the volumetric reaction model, you don't need to know the mechanism.

Just specify a reaction A -> B. By default, FLUENT uses a power-law Arrhenius model, so you need to put in:
a) stoichiometry (do make sure the molar mass of reactants and products matches
b) power-law exponents (for a first order reaction, set it to 1 for reactant A)
c) pre-exponential factor and activation energy (this determines the rate)

Alternatively, you can supply other kinetics than power law via a UDF. But you never need to know the exact mechanism.

Sara28 · July 30, 2015, 02:47

Thanks for your answer

Is it possible to use this way doing surface reactions ?

gustavosimiema · July 30, 2015, 04:02

Hi Sara,

are you working with atmospheric pressure or low pressure?

Sara28 · July 30, 2015, 04:35

most probably with atmospheric pressure. Right now it is very confusing because i don´t know all the conditions yet. I know that i have a chemical reaction between a gas and a solid. And they react on the surface to a gas and a solid. Important is that i simulate how the gas flows around the solid and how the gas formed by reaction on the surface flows away from the solid. It is so difficult for me!

is it even possible to do?

gustavosimiema · July 30, 2015, 04:44

I´m also beginner... but I i think it is possible. But you will have different behaviours of the flow depending on the operating pressure.

Sara28 · July 30, 2015, 04:47

I try it first with atmospheric pressure. I wondered if there´s a way to do it like take a gas through the inlet and to say there´s a gas flowing from the surface. Mavbe with source term UDF or something. But i don´t know how. Or is it a stupid idea?

gustavosimiema · July 30, 2015, 04:50

I never worked with UDF, but how is your chamber geometry. Because if you have your inlet and outlet... the gas will flow in this direction... then with the streamlines or maybe vector plot you can see how the gas will flow in the surface..

Sara28 · July 30, 2015, 05:02

I made a little sketch. I hope it can help.

gustavosimiema · July 30, 2015, 05:10

So, I have not yet worked with reactions. But I would suggest in a first step to simulate just the flow in order to understand this behaviour and then start with the reactions. What do you think? Because maybe in this step you can figure out that your inlet is not in the best place or certify that it is ok.

Sara28 · July 30, 2015, 05:17

Yes, you are right! I go first without the chemical reaction! Thank you!

But then i have to find a way including the reaction but i think there is too much i don´t know about the chemistry, because it´s a new chemical process which we develop here at university. So i thought maybe doing it without real material properties but i don´t know if that brings good results.

I appreciate every advice!

July 30, 2015, 01:40	chemical reaction	#1
Sara28 New Member Join Date: May 2015 Location: Germany Posts: 15 Rep Power: 11	Hello together, is there any way to do chemical reactions without knowing the reactionmechanism? Just to see where the fluid flows and where the products after the reaction occur? Thanks for your advices! Sara

July 30, 2015, 02:40		#2
CeesH Senior Member Cees Haringa Join Date: May 2013 Location: Delft Posts: 607 Rep Power: 0	Hi, If you use the volumetric reaction model, you don't need to know the mechanism. Just specify a reaction A -> B. By default, FLUENT uses a power-law Arrhenius model, so you need to put in: a) stoichiometry (do make sure the molar mass of reactants and products matches b) power-law exponents (for a first order reaction, set it to 1 for reactant A) c) pre-exponential factor and activation energy (this determines the rate) Alternatively, you can supply other kinetics than power law via a UDF. But you never need to know the exact mechanism. Sara28 likes this.

July 30, 2015, 05:10		#10
gustavosimiema Senior Member Gustavo Join Date: Jun 2015 Posts: 121 Rep Power: 10	So, I have not yet worked with reactions. But I would suggest in a first step to simulate just the flow in order to understand this behaviour and then start with the reactions. What do you think? Because maybe in this step you can figure out that your inlet is not in the best place or certify that it is ok. Sara28 likes this.

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July 30, 2015, 02:47		#3
Sara28 New Member Join Date: May 2015 Location: Germany Posts: 15 Rep Power: 11	Thanks for your answer Is it possible to use this way doing surface reactions ?

July 30, 2015, 04:02		#4
gustavosimiema Senior Member Gustavo Join Date: Jun 2015 Posts: 121 Rep Power: 10	Hi Sara, are you working with atmospheric pressure or low pressure?

July 30, 2015, 04:35		#5
Sara28 New Member Join Date: May 2015 Location: Germany Posts: 15 Rep Power: 11	most probably with atmospheric pressure. Right now it is very confusing because i don´t know all the conditions yet. I know that i have a chemical reaction between a gas and a solid. And they react on the surface to a gas and a solid. Important is that i simulate how the gas flows around the solid and how the gas formed by reaction on the surface flows away from the solid. It is so difficult for me! is it even possible to do?

July 30, 2015, 04:44		#6
gustavosimiema Senior Member Gustavo Join Date: Jun 2015 Posts: 121 Rep Power: 10	I´m also beginner... but I i think it is possible. But you will have different behaviours of the flow depending on the operating pressure.

July 30, 2015, 04:47		#7
Sara28 New Member Join Date: May 2015 Location: Germany Posts: 15 Rep Power: 11	I try it first with atmospheric pressure. I wondered if there´s a way to do it like take a gas through the inlet and to say there´s a gas flowing from the surface. Mavbe with source term UDF or something. But i don´t know how. Or is it a stupid idea?

July 30, 2015, 04:50		#8
gustavosimiema Senior Member Gustavo Join Date: Jun 2015 Posts: 121 Rep Power: 10	I never worked with UDF, but how is your chamber geometry. Because if you have your inlet and outlet... the gas will flow in this direction... then with the streamlines or maybe vector plot you can see how the gas will flow in the surface..

July 30, 2015, 05:17		#11
Sara28 New Member Join Date: May 2015 Location: Germany Posts: 15 Rep Power: 11	Yes, you are right! I go first without the chemical reaction! Thank you! But then i have to find a way including the reaction but i think there is too much i don´t know about the chemistry, because it´s a new chemical process which we develop here at university. So i thought maybe doing it without real material properties but i don´t know if that brings good results. I appreciate every advice!