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Modelling chemical reactions without considering heat transfer

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Old   December 16, 2017, 05:51
Default Modelling chemical reactions without considering heat transfer
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Hi,

This is a branch of an ongoing discussion in another thread, I thought it might be good if I post it separately, sorry for repetition.

I am trying to model a set of chemical reactions in CFX, currently using variable composition mixture + reaction rates as source terms.

To benefit from the built-in functionality of CFX, I assume need to define a reacting mixture + reactions. This needs me inclusion of heat capacities (i.e., heat transfer) as well. I do not want to include any heat transfer in this model.

Does anybody have any advice how to use reactions in CFX, without inclusion of heat transfer?

Many thanks.
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Old   December 16, 2017, 07:19
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If your question is how do I model endo/exothermic chemical reactions but not model heat transfer - then the answer is you can't. You need the heat transfer model to capture the heat released and absorbed. If other heat transfer processes like heat transfer at the walls is effectively zero, then why not just model the walls as adiabatic? In other words, use a heat transfer model, but only include significant bits of the heat transfer and everything else can be adiabatic.
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Old   December 16, 2017, 08:23
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Thanks a lot Glenn. My problem is that I do not have any information about heat of reaction or enthalpy of the reactions that I am going to model. Moreover, temperature and heat transfer are not really important for me in these simulations.

Thats why I first chose to create a variable composition mixture and define reactions as source terms.

So, from what I understood if I want to use CFX built-in functionality for defining chemical reactions then I have to have hear transfer as well, is there any trick to turn off energy equations or at least make them passive by entering some nonsensical values for heat capacities, etc.
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Old   December 16, 2017, 19:22
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I see, you are not interested in the temperature field at all.

Are you sure you need the heat equation with chemical reactions? I do not do chemical modelling so am not familiar with it. The heat equation does not add much overhead to the solution so I would not be too worried about solving it. You won't save much by stopping it.

But if you really want to stop it you can use the expert parameters to turn the heat equation solution completely off. The keyword is something like "solve heat" as an expert parameter.
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