Is it possible to use FLUENT to examine the convective flux?

Hi,

In my case, the porous particle is placed in the air and some reactions happened only in the particle zone. the concentration of species in the particle will be affected by the convective flow and diffusive flow. So far, what I know is that the Fluent can calculate flow rate for each species on certain surface. But it is a "general" flow rate which can not distinguish the amount of convective flow rate and diffusive flow rate.

So, Is it possible to use FLUENT to examine the convective and diffusive flow individually for certain species?

Another question is, when I plot the velocity vector, the direction pointing out which is leaving the system. But when I calculate mass flow rate, it is a positive value (positive means going in the system, right?). The selected area is the same. Is this because I used the wrong coordinate system? 

Thanks!

 
 

Comments

  • KremellaKremella Forum Coordinator
    edited June 29

    Hello,

    1st question - Can you clarify what you mean by diffusive flow? Are you referring to the diffusion of your species concentration?

    Regarding the second question - yes, positive is into the system and -ve means leaving the system. Are you looking at an outlet boundary or are you estimating the mass flow rate at the internal face? If this is at an internal face, the area vector might be pointed in the direction opposite to the velocity vector and therefore you might be getting a negative value.

    Thanks.

    Karthik

     

  • wuxuetianziwuxuetianzi Member
    edited June 30

    Hi, thank you for your reply. 

     

    For the first question, yes, I am referring to the diffusion of the species concentration. Also, the reactants are going into the system like O2, and products are going out like CO. However when I calculate flow rate on the particle surface (internal face) by using "surface report" - "Flow rate" - "mass fraction of O2/CO", I get a positive value for both of them. After doing the same process for all species, all of them have a positive value for the Flow rate on the surface. does this mean that there only has flow going inside on the surface? It seems not realistic. did I do something wrong to measure the flow rate for each species individually?  

     

    The convective flux can be considered as "Stefan flow", How can I measure it in the FLuent?  

     

    Now, for the second problem, if all the species have a positive flow rate that is going into the surface, why can I get the vectors with the arrows pointing out on this surface?  

     

    Thanks!   

     


     

     
  • wuxuetianziwuxuetianzi Member
    edited June 30

    Hi, is my problem solvable? Please let me know if you need more information. Thanks!

  • KremellaKremella Forum Coordinator
    edited July 1

    If you are seeing positive values of mass flow rate, it means that the flow rate is into the boundary.

    Also, regarding your vector plots - could you please share screenshots of the issue you are talking about and how you are plotting this?

    Thanks.

    Karthik

  • wuxuetianziwuxuetianzi Member
    edited July 1

    Hi, here is the plot for the vectors for the surface.

     Once I want to insert image from browse, it says "Sorry an error occurred". Any suggestions? Thanks

    As you can see, all the narrows are pointing out, and the values are all positive. So, for the same surface, how all species flow rates are going into the system?

  • KremellaKremella Forum Coordinator
    edited July 2

    Yeah, I noticed this error too yesterday. Our IT team has resolved the issue.

    I'm simply testing to see if I can attach an image here. Please ignore the image. 

    Please post your image again here.

    Thanks.

    Best,

    Karthik

  • wuxuetianziwuxuetianzi Member
    edited July 2

    Here is the plot for the vectors for the surface.

    As you can see, all the narrows are pointing out, and the values are all positive. So, for the same surface, how all species flow rates are going into the system?

    I calculate the flow rate for each species as

    I am wondering if the way to report or plot is correct. 

    Thanks!

     
  • KremellaKremella Forum Coordinator
    edited July 6

    Could you please go into 'Custom Vectors' and create a vector for 'Area' (please see the plot below)?

    Plot this Area Vector as well as the velocity vector on your surface of interest. Are these two in different directions?

    Thank you.

    Karthik

  • wuxuetianziwuxuetianzi Member
    edited July 7

    Hi, Thanks for your suggestions. However, when I was following your step, I got nothing showing up after I click "display"...I have adjusted my view, but nothing changes.

     
  • KremellaKremella Forum Coordinator
    edited July 8

    That's weird. Could you please display just the surface for me?

    Thank you.

  • wuxuetianziwuxuetianzi Member
    edited July 8

    Hi, I think I figure out the reason. There is something that showed up, just too small...  I circled them below.  

    If it is helpful, I also plot the surface.

    Is there any other way?

    Thanks!

  • KremellaKremella Forum Coordinator
    edited July 9

    Let me ask you this - how did you create this surface? And where is this surface present in your geometry? Please provide a screenshot of the geometry and show the relative position of this surface under investigation?

    Also, what quantity are you plotting here? What is the legend value highlighting?

    Thanks.

    Karthik

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