Learning Forum

[SR786]

Hi,

I am interested in modelling a semi-batch STR with a vortex, where I will be feeding species A to the vessel which is pre-loaded with species B, where two species will react in the liquid phase. The volume of the vessel will change significantly over the feed addition period (i.e., from 5 L to 8 L). I am considering using the VOF model (for accounting for interface) coupled with species transport (for species and chemical reaction). One thing I wanted to ask is will the CFD solver automatically account for dilution effects, i.e., decrease in concentration due to volume increase, or do I need to add a dilution term to the CFD equations?  

[Rob]

If you're adding the second species into the liquid (ie under the free surface) then mass, volume, concentration etc will be handled by the solver. Don't forget to leave sufficient head space and have an open boundary at the top of the tank. In the above the liquid phase would be a species mixture. 

There are a few examples in Help but can't remember if there's a public tutorial at present. 

[SR786]

Thank you for the prompt reply. Also I wanted to later on model precipitation by incorporating PBEs. The framework I am considering is:

• Inhomogeneous Eulerian Multi-Fluid VOF
• Species Transport
• PBM (Method of Moments)

For this framework, do I just need to add UDFs to define supersaturation in addition to nucleation and growth kinetics as well as a source term for the consumption of my species which form a crystal. I also noticed there is an option for heterogeneous reaction under the phase interaction tab. Do I need to select this to or do I just neglect it?

 

[Rob]

If the reaction is within a phase (ie liquid + liquid) you have the choice of using the above or a volumetric reaction in Species model. If you're looking at liquid+liquid=>solid then that's a phase interaction. You'll then need a solid (granular) phase to handle the PBM etc.  

PBM is covered in the manual, but I think there's also some content in the Ansys Learning Hub. As staff I can only help within the bounds of public knowledge and the documentation so I suggest reading that to cover what you need now and what you want in future.