Fluids

Fluids

Species conservation

    • Sowmiya
      Subscriber

      Hi,


         I am simulating plasma jet discharge using FLUENT software. I consider volumetric reactions in species transport panel and include certain number of reactions in reaction panel.


      In order to solve the conservation of chemical species in jet , the local mass fraction of each species ,Yi, has been calculated from the transport equation of that species. The conservation equation takes the general form as shown in equation attached.


      where 'Ji ' is the diffusion of species i, 'Ri ' is the rate of production of species i by chemical reaction and Si is the rate of production from any source.


      Whether 'Ri ' term will be included automatically when the volumetric reaction option is selected in species transport panel or it has to be included through DEFINE_VR_RATE macro in UDF and hooked in User-Defined Function Hooks panel ?. 


      please kindly give me some suggestion. I referred user guide and UDF manual many times but i am not getting cleared.


      Regards


      Sowmiya

    • RK
      Ansys Employee

      Hello, 


      As Ansys employees, we will not able to view attached files. Can you please insert an image instead so that we can better assist you?


      Regards,


      Rahul 

    • Sowmiya
      Subscriber

      Hi Sir,


           Thanks for your respond and sorry for the inconvenience. I have inserted the image below. Please kindly give me some suggestions.



      Regards


      Sowmiya

    • RK
      Ansys Employee

      Hello, 


      To understand better the rate of production of species and how it is calculated in Ansys Fluent, please refer to the theory guide. 


      https://ansyshelp.ansys.com/account/secured?returnurl=/Views/Secured/corp/v201/en/flu_th/flu_th_sect_finite_rate.html


      Depending on the problem specification and your end results, you will enter the values accordingly in Ansys Fluent. 


      Regards, 


      Rahul 

    • Sowmiya
      Subscriber

      Hi Sir,


          Thanks for your suggestion and supporting me.


         Sorry to inform you that I have trouble in logging in Ansys customer portal now as our technical support service is expired but I have theory guide of ansys fluent downloaded from this website.


      Whether you are requesting to refer chapter 7:Species transport and finite rate chemistry from theory guide.?


      My problem is to determine the concentration of individual species w.r.t temperature in the plasma jet discharge by solving the species conservation equations.


      I included the reactions in the reaction panel with the arrhenius parameter by selecting the volumetric reaction. The mole fraction of individual species obtained is not satisfactory with the values from Free Energy Minimization calculation. I want to clarify whether the methodology of input parameters is correct ?


      Kindly give me few suggestion regarding the issues.


       


      Regards 


      Sowmiya

    • Rob
      Ansys Employee

      Check the mesh, convergence and also the chemistry you've defined.  How far off the expected values are you, and what assumptions does that calculation route take compared to your set up in Fluent. 

    • Sowmiya
      Subscriber

      Hi Sir,


            Thanks for your suggestions. whether mesh would be the reason for this issues? In which way it would affect the solution?  I have used gradient quadrilateral mesh, the region to be resolved are given fine meshing and other regions are given coarse mesh. 


      Regards


      Sowmiya

    • DrAmine
      Ansys Employee
      how are u quantifying species conservation? How does convergence behavior look? Which solver are you using,? Which species resction model is used?
    • Sowmiya
      Subscriber

      Hi rwoolhou


            Thanks for your reply and supporting me. The calculated value from fluent is very less compared to the expected value. And this makes me to doubt whether the species conservation equation includes the reactions included in the reaction panel and the rate of production (Ri) of species i by chemical reaction are included ? or whether UDF should be used to implement this term in species conservation equation?


      Expecting your suggestions for this issue.


      Many thanks


      Sowmiya

    • Sowmiya
      Subscriber

      Hi abenhadj


                  Thank you for your response towards my queries. The species conservation are quantified to determine the concentration of individual species w.r.t to temperature in computational domain.


      I have simulated plasma jet in two cases - laminar jets and turbulent jets. In the case of laminar, i used finite rate formulation with none-explicit solver whereas in turbulent plasma jet i used k-epsilon 2-equation model with eddy-dissipation concept.


      Dissociation of N2 reactions are included in the reaction panel and the reactions are taken from literature.


      My doubt is that whether the species conservation equation includes the reactions included in the reaction panel and the rate of production (Ri) of species i by chemical reaction are included ? or whether UDF should be used to implement this term in species conservation equation?


      Please let me know your thoughts on it.


      Really I appreciate all for their response to my queries and supporting me. And sorry for the late reply due to improper net connection.


      Many Thanks 


      Sowmiya

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