Learning Forum

[Jobre]

Hi,

I'm simulating a chemical reactor with a reaction bed and a separate cooling pipe in Fluent 19. They are both embedded in a solid.

In the cooling I use water which evaporates due to the high temperatues of the solid caused by the reaction.

I'm currently using the Multiphase Mixture model with 3 phases:

-reaction mixture (inlet reaction)

-water liquid (inlet cooling)

-water vapor (created in the cooling channels)

 

I defined all the reactions in the "Materials" setup, but somehow cannot connect them with the belonging cell zone

Now here are some questions:

1. How to connect the reaction with the cell zone conditions of the reaction bed? How to enable the Chemistry Solvers?

2. Which is the best/most convenient way to include the reaction kinetic?

3. Does it matter which phase I choose as primary/secondary?

 

Thanks in advance!

[Rob]

As ANSYS staff we're limited in scope to assist: this isn't a simple problem to be able to give a generic answer to. 

Your system has two separate fluid zones, and multiphase flow. You also want a chemical reaction in the system, but I'm unsure whether the reaction produces water, or evaporates what is already there. 

Can you sketch out the layout, and detail what goes into the system where then it may be possible to give some advice. 

 

In terms of primary & secondary phases, it's dependent on what's going on in the system. I suspect you want all the liquids in one phase and vapour in the other, but hopefully the sketch will clarify. 

[Jobre]

 

Yes I have 2 seperate fluid zones embedded in 1 solid:

1. In the cooling channels I insert liquid water, which evaporates due to the high temperatures. Thus, I get almost completely gaseous water at the cooling outlet.

2. I use a gaseous mixture for a methanation process (mainly: CO2 + 4H2 <-> CH4 + 2 H20). This reaction produces heat, which increases the temperature of the solid and causes the water in the cooling channels to evaporate.

 

I use 3 phases:

1. water_liquid (primary)

2. water_vapor (secondary)

3 reaction mixture (secondary)

 

The evaporation works fine so far with the mixture model.

However I'm not completely sure about the reaction part. I can connect the reaction with the belonging cell zone, however I'm not able to include the Chemistry Solvers in "Species" like in Fluent 16.

So here are the questions:

1. How do I correctly calculate the reaction? How to enable the Chemistry solvers (Stiff Chemistry Solver)?

2. Is there an included way to adjust the reaction kinetic in Fluent without using UDFs? If not where can I find a good UDF tutorial for chemical reactions for Fluent 19?

3. Is the determination of primary and secondary phases fine or should I declare them differently?

 

Thanks!

[Rob]

I would start by simplifying the system. 

Build one model and figure out the chemistry (not trivial, and I'd look at the Arrhenius chemistry set up). 

Build a second model that looks at a hot volume and evaporation. 

Once you understand these try to combine the models. Currently you've got two fairly complex interacting models and trying to troubleshoot both at once will be difficult.