setting the bulk species

- June 6, 2019 at 4:51 pm
  
  Zari
  Subscriber
  
  Hi,
  
  I have a 2D geometry, with 2 inlets, modeling fluid dynamics and species transport (including reactions).
  
  Two species (CH4, CO2) are injected from 1 inlet, and 2 species (O2, CO2) are injected from the second inlet.
  
  So I know that CO2 has the highest mass fraction, considering both inlets.
  
  These species all react with each other, even CO2. The reaction mechanism is imported and it contains of some other intermediate radicals and few other products.
  
  There is not any inert bulk specie at the inlets, that I can choose as the bulk specie. Everything is reacting in the system.
  
  Which specie should I set as the bulk?
  
  CO2? Then it disappears in the species list and I cannot even set the inlet values for it.
  
  Does not this affect the production and consumption of CO2 due to reactions?
- June 10, 2019 at 8:19 am
  
  Zari
  Subscriber
  
  Any ideas about this?
- June 10, 2019 at 10:24 am
  
  Rob
  Forum Moderator
  
  Lots, please remember that staff work Monday-Friday in whatever timezone they're in and have many other tasks to take care of.
  
  We set the most common species as the "bulk" because Fluent solves n-1 species with the remainder being the "bulk". If CO2 is the bulk (probably the correct choice given it's a combustion problem) you set the inlets to be the volume fraction of whatever else is there:
  
  1 - (sum other volume fractions) = CO2 volume fraction.
- June 11, 2019 at 1:39 pm
  
  Zari
  Subscriber
  
  Thank you so much for the solution. I updated the kinetics and have applied the model settings and started running the model. It is still in the first iterations, but as I checked the species-mass-flow, the flow rates look correct.
  
  The only doubt I still have is the effect of setting a specie as bulk-specie on the reactions that specie involved in. I mean will the production and consumption of the bulk specie be calculated for all reactions that it supposed to be involved, as the reaction mechanism says?
  
  This is specially more important where in some cases the oxygen flow rate is a bit higher than CO2, so what if I set oxygen as the bulk specie? Since o2 is the oxidizer and the main reactions depend on it, is there a risk of missing reactions to be calculated?
- June 11, 2019 at 2:30 pm
  
  DrAmine
  Ansys Employee
  
  The bulk specie is not solved That is just constraint. The source terms (sinks and sources) due to the reactions to the bulk species will be source terms affecting other transported species so do not worry on that.
- June 13, 2019 at 1:23 pm
  
  Zari
  Subscriber
  
  Thank you so much.