Introduction – Defining the Problem

  • Lithium-ion cells of production level EV operate optimally within a narrow temperature range between 25 ◦C and 40 ◦C.

  • The main issue with Li-ion battery heat is thermal runaway, which causes rapid temperature rise, gas generation, and potential explosions.

  • A Battery Thermal Management System (BTMS) is a system designed to regulate and maintain optimal temperatures in a battery pack, ensuring safety and efficiency.

Working of a BTMS

  • A BTMS works by monitoring the battery pack's temperature and employing cooling mechanisms to maintain optimal conditions.

  • It uses components like fans, pumps, or thermoelectric devices to circulate air or liquid coolants, effectively dissipating heat.

  • Active BTMS uses external energy and components, while passive BTMS relies on materials and design features


Assumptions


Problem Setup

  • The flow is incompressible (constant density).

  • The flow is laminar.

  • The system involves prismatic battery cells.

  • The domain is a 2D top view.

  • The battery material is isotropic.

  • The influence of buoyancy is ignored.

  • Convection and conduction are the primary heat transfer modes; radiation is neglected.

  • The cells are treated as constant heat sources.

Fluid Flow

  • We use a staggered grid with ghost nodes, defining u, v, P, and T as the primitive variables.

  • The Navier-Stokes equations are solved using:

    1. The Pressure Poisson equation to simulate 

    fluid flow.         

    2. The Energy equation is solved simultaneously,

    to account for heat dissipation.













































  

    
  
    

      

        

          

          
          

          
            
              

                
            
            
            
            
            
            
            

            
              
            
            

          
              

            
          

        

      

    

    
  


  














































  

    
  
    

      

        

          

          
          

          
            
              

                
            
            
            
            
            
            
            

            
              
            
            

          
              

            
          

        

      

    

    
  


  







  
Initial and Boundary Conditions ( for Velocity and Pressure)
























  
  















































  

    
  
    

      

        

          

          
          

          
            
              

                
            
            
            
            
            
            
            

            
              
            
            

          
              

            
          

        

      

    

    
  


  







  
Initial and Boundary Conditions ( for Temperature)























  
  















































  

    
  
    

      

        

          

          
          

          
            
              

                
            
            
            
            
            
            
            

            
              
            
            

          
              

            
          

        

      

    

    
  


  




    

  
  

  



  
    
    


  
  




  

    

    
      
    
    

  

  

    

      
      
      
      
      
      
      
      
      







  
    

  
  







  
Parameters























  
  











  
    

  
  







  
Density (rho) - kg/m3
Specific Heat (Cp) - J/kg.K
Thermal Conductivity (k) - J/m.K.sec























  
  








  
Parameters for Fluids and Battery Cells
























  
  











  
    

  
  







  
Battery Cell (LiFePO4)























  
  











  
    

  
  







  
 
2047
1605
0.15























  
  











  
    

  
  







  
Fluid-1 (Novec - 7000)























  
  











  
    

  
  







  
 
1400
1300
0.075























  
  











  
    

  
  







  
Fluid-2(Air)























  
  











  
    

  
  







  
 
1293 
1005 
0.025























  
  





    

  
  

  



  
    
    


  
  




  

    

    
      
    
    

  

  

    

      
      
      
      
      
      
      
      
      




  
Fluid-1 (Novec 7000)
























  
  








  
Fluid-2 (Air)
























  
  








  
Results























  
  








  
Immersion cooling vs Air Cooling























  
  








  
Immersion cooling mitigates thermal runaway risks by enabling superior heat dissipation compared to air cooling























  
  





    

  
  

  



  
    
    


  
  




  

    

    
      
    
    

  

  

    

      
      
      
      
      
      
      
      
      




  
Temperature & Velocity -Contour Plots for Various Cell Spacing
























  
  








  
Increasing battery spacing enhances thermal performance by reducing final battery temperature























  
  








  
Cell Spacing= 0.04 m























  
  















































  

    
  
    

      

        

          

          
          

          
            
              

                
            
            
            
            
            
            
            

            
              
            
            

          
              

            
          

        

      

    

    
  


  







  
Cell Spacing= 0.02 m























  
  








  
Cell Spacing= 0.04 m