Learning Forum

[shyamal.bhunia]

Hi all,

Can anyone share a tutorial or any material on 'modelling packed bed combustion in fluent'? As per my understanding, it has to be modelled using the Euler- granular multiphase model. I have access to various tutorials on fluidized bed combustion. Packed bed combustion is simpler compared to FB combustion since the bed becomes static for the latter. I have tried with many tweaks, but it doesn't give meaningful results. after many trials, I was able to develop an acceptable case, but with that, any changes regarding the solid phase don't work; I can't able add more reactions to the case as it diverges.

Many a time, it shows a warning message as follows.

....................................................................................................................

temperature limited to 1.000000e+00 in 63 cells on zone 628 in domain 2

temperature limited to 1.000000e+00 in 189 cells on zone 628 in domain 2

temperature limited to 1.000000e+00 in 196 cells on zone 628 in domain 2

temperature limited to 1.000000e+00 in 281 cells on zone 628 in domain 2

temperature limited to 1.000000e+00 in 77 cells on zone 628 in domain 2

temperature limited to 5.000000e+03 in 1 cells on zone 628 in domain 2

.......................................................................................................................

 

kindly share your opinion.

[Rob]

What was the time step, and what volume fraction did you patch into the domain? The only tutorials I can suggest are on the Help system (don't think there is anything) and potentially the Learning Hub (you need a subscription) or Customer Portal (your supervisor may have access). 

[shyamal.bhunia]

Hi Rob,

Thanks for responding!

I'm trying to simulate it for a steady state. I don't patch the volume fraction of the solid phase; instead, the components in the solid phase are given as sources in the packed bed zone.

Our institute has licensed Ansys, so it won't be a problem to access Ansys help. Can you suggest to me the links that I can refer to in the Learning Hub? I already contacted the customer portal but was unsuccessful in solving the problem. 

Kindly share if you know of anything that would help me in solving the problem. I can also share my case and data file if you require.

Thank again!

[Rob]

If you're using a source term you're adding that amount of material at the defined rate. I'm not sure how that will interact with the static bed. 

On the ALH there's the multiphase course, but that doesn't have anything on the fixed bed part - I'm just about to review the lecture, once I finish the DPM one and log off from here! 

The advantage of the Community is that anyone or everyone can help, however that means we (staff) can't take any files or communicate in anyway other than here - it's noted (or was) in the rules you may have read when you registered. 

[shyamal.bhunia]

Hi Rob,

The solid phase species sources I supply eventually undergo heterogeneous reactions (through phase interaction) and generate species in the gas phases. Subsequently, gas-phase reactions happen. Could you please clarify what you meant to say by  "I'm not sure how that will interact with the static bed". 

Kindly revert with some materials you think would be helpful for this particular case.

Thanks!

[Rob]

You're adding material to a static bed - note STATIC. Where is the mass going if the original bed isn't moving? 

[shyamal.bhunia]

The static bed is just a porous bed with a low secondary phase volume fraction at the beginning of the value we patch. The mass added to the bed is converted to gaseous species through heterogeneous reactions, as discussed in the last post. The bed doesn't move; if some mass sources are not reacting, it just increases the volume fraction of the bed.

[Rob]

And did you tick the packed bed option? 

[shyamal.bhunia]

Yes I always enable the packed bed option on, and in the cell zone set the x, y, z velocity to fixed value 0 m/s.

[Rob]

How much mass are you adding? How does the volume fraction of bed look? 

[shyamal.bhunia]

The mass source is at 0.2 kg/m3s.  The volume fraction is uniform throughout the bed, the value remains at 0.3-0.5.

[Rob]

Odd. Is the reaction uniform through the bed or focussed at one end? If the system is steady you're effectively modelling the equilibrium condition: with multiphase that can be domain empty or full. With fixed bed I'm not sure how "full" will behave. What is the source energy to raise the temperature of the added solids?