General Mechanical

General Mechanical

Incorrect thermal model

    • Battery
      Subscriber

      I have some issues with the thermal models of pouch cells in serie configuration. As example the thermal model of 4 battery pouch cells in series has exactly the same maximum temperature as one cell. Also cell 1 & 4 in the battery pack should be the same whilst the two cells in the middle (cell 2&3) should be hotter because the accumulated heat in the middle of the pack is more difficult to dissipate.


      What I am doing wrong? Reviewed my project several times but can't find any issues. Only thing I'm not sure about is: do I need to define the areas between the cells as air?




       


      I do get this warnings and I already did run the command "/mesh/modify-zones/slit-interior-between-diff-solids parallel" but it doesn't change the models.


       



       

    • Battery
      Subscriber

      To add to my question:


      The images below are from the paper: "Transient Temperature Distributions on Lithium-Ion Polymer SLI Battery" by Yiqun Liu, Y. Gene Liao * and Ming-Chia Lai. This paper describes how the thermal models should look like. It says that the cells in the middle have the highest temperature because heat accumulated in the middle of the pack is more difficult to dissipate.



    • spatel
      Ansys Employee

      Are the cells actually in contact with each other and also what are the thermal boundary conditions to dissipate the heat - convection boundary.

    • Battery
      Subscriber

      Are the cells actually in contact with each other and also what are the thermal boundary conditions to dissipate the heat - convection boundary.



      Yesterday I made a new project and tried to remake the battery in the paper with the same dimensions to compare results and to verify my working method. This is what happens when boundary conditions are the same on all the cell walls: 


       



      This is the result when I remove all boundary conditions on the cells in the middle. This clearly looks much better and compares better to the results in the paper. The cells have 3 to 7mm space in between them. The space is filled with air in the simulation (also was wondering if I need to define this area with air?). At the cells on the outside convection happens and the cells on the inside conduction I suppose? Anyway I'm not sure how I can use conduction in Ansys.





      Here you can see the boundary conditions used on the cells on the outside. But what should I use for the cells on the inside because conduction isn't listed in the BC interface. I found shell conduction but this asks me for a wall thickness.


       


    • Battery
      Subscriber

      I had a response from the writers of the paper and they told me that you need to add an air volume between the cells. How can you do this?

    • spatel
      Ansys Employee

      Thanks for the additional information.


      From the last two images you shared it is clear that there is a physical gap between the cells being modelled. And this gap is not meshed and so not modelled - hence this means conduction cannot be accounted since there is no mesh in the gap. 


      So either:


      - mesh the gap in between the cells and model the air (accurate and solver works out heat transfer to/from the air gap) - make sure to have at least 3 prism layers close to the battery cell faces)


      or


      - you modify the thermal boundary conditions of cells faces that are facing each other to have have lower heat transfer which is what would happen as the heat transfer coefficient and air temperature in between cells will be higher.


      First option makes good sense in your case as in the other option you will have to somehow try to find suitable heat transfer coefficient and air temperature values which will need to be approximate somehow as these are not typically available 


       

      • ali.abbas
        Subscriber

        Hi Spatel,

         

        Just a small question if i desgined a solid body which is directly connected to the cells and considered this body as fluid region in ansys fluent, does it do the job?

    • Battery
      Subscriber

      Thanks Spatel.


      I did mesh the gap between the cells and this solved the issue. Unfortunately this isn't covered in the tutorial. You can see the result below:



      But I don't really understand why we have to do this. If the air between the cells needs to be meshed, why the air on the outside of the cells doesn't need a mesh? 


       

    • Battery
      Subscriber

      Bump

      • ali.abbas
        Subscriber

        dear battery how did you add the volume of air between the cells?

    • Rob
      Ansys Employee

      On the outside of a cell we can add an external HTC and temperature, between the cells (I assume) you're expecting to see heat transfer so we need to include that in the model. 

    • AngelFalls
      Subscriber
      Dear Battery, did you use any boundary condition for the air domain? Which solution method did you use? Thank you.n
Viewing 9 reply threads
  • You must be logged in to reply to this topic.