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-   -   Problem with Volumetric Reactions in Fluent (https://www.cfd-online.com/Forums/fluent-udf/142550-problem-volumetric-reactions-fluent.html)

Kashif Rashid October 4, 2014 04:52

Problem with Volumetric Reactions in Fluent
 
1 Attachment(s)
I have written UDF in C, using fluent macro, “DEFINE_ADJUST”, for internal steam reforming (file attached). Reforming reactions have to take place inside porous anode electrode of Fuel Cell. Pre-reformed fuel mixture is used which consist of (CH4, H2, H2O, CO, CO2). The source terms are hooked in "Cell Zone Conditions" of fluent. UDMI, memories in Fluent are also allocated to store data for above terms (see code file). Initialization and msr_adj are also hooked, segregated solver is used. Energy, species models are tern on.

After doing all these things and running simulation, reactions are not taking place; there is no change in concentration of species at inlet and outlet.
However, when I selected Volumetric Reactions in the Fluent, second Laminar Finite-Rate, third the values of Pre-Exponentional Factors and Activation Energies are adjusted to my own required Arrhenius Rate, and fourth, stoichiometric coefficients are also set according to reforming and shift reactions.

After making above mentioned changes, plus using UDF, reactions are taking place. Because of these issues, I want to know/clarify following things:-

1. Is it necessary or mandatory to activate the Volumetric Reactions within the Fluent in the presence of UDF ??

2. Will this activation of Volumetric Reactions duplicate the calculations. Because i want to incorporate my own rate modeling through UDF whereas, Fluent is using Arrhenius Rate model. Which model is executed during simulation ?

3.Can i modify fluent Arrhenius rate model and other setting according to my own requirements ???

a.hazarika October 17, 2016 08:54

Hello,

I am also trying to write a UDF for water gas shift reaction. But the problem is I am not getting any change in result as expected with change in activation energy. What can be the problem?

sooraj546 December 28, 2017 01:36

Quote:

Originally Posted by Kashif Rashid (Post 512863)
I have written UDF in C, using fluent macro, “DEFINE_ADJUST”, for internal steam reforming (file attached). Reforming reactions have to take place inside porous anode electrode of Fuel Cell. Pre-reformed fuel mixture is used which consist of (CH4, H2, H2O, CO, CO2). The source terms are hooked in "Cell Zone Conditions" of fluent. UDMI, memories in Fluent are also allocated to store data for above terms (see code file). Initialization and msr_adj are also hooked, segregated solver is used. Energy, species models are tern on.

After doing all these things and running simulation, reactions are not taking place; there is no change in concentration of species at inlet and outlet.
However, when I selected Volumetric Reactions in the Fluent, second Laminar Finite-Rate, third the values of Pre-Exponentional Factors and Activation Energies are adjusted to my own required Arrhenius Rate, and fourth, stoichiometric coefficients are also set according to reforming and shift reactions.

After making above mentioned changes, plus using UDF, reactions are taking place. Because of these issues, I want to know/clarify following things:-

1. Is it necessary or mandatory to activate the Volumetric Reactions within the Fluent in the presence of UDF ??

2. Will this activation of Volumetric Reactions duplicate the calculations. Because i want to incorporate my own rate modeling through UDF whereas, Fluent is using Arrhenius Rate model. Which model is executed during simulation ?

3.Can i modify fluent Arrhenius rate model and other setting according to my own requirements ???

How did you change it to volumetric reactions do u meant using DEFINE_VR_RATE ?


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