Guidance needed for Conjugate Heat Transfer Analysis for a 3s3p Li-ion Battery

[zulfikar.jasdanwala23]

I am performing a conjugate heat transfer (CHT) analysis of a 3s3p battery pack to evaluate the effect of copper plates on thermal management. As a baseline for comparison, I am first analyzing the pack without copper plates.

For validation, I am using data from a research paper that experimentally analyzed a 3s3p pack under a 3C discharge rate. The paper reports a volumetric heat generation of 170,000 W/m³ within the cells, which I have applied as a cell zone heat source in my simulation. At the cell walls, I specified a convective heat transfer coefficient of 5 W/m²K (taken from youtube). The goal is to compare the simulated maximum cell surface temperature with the experimental results to validate the model.

The mesh is done in fluent with 6 layers of inflation.

The simulation setup is transient, run for 700 s with a timestep of 1 s, using the k–ε turbulence model. Inlet and outlet boundary conditions are left at default settings, and all walls are coupled by default.

The issue I am facing is that the cell surface temperature continuously increases linearly with time (as shown below) and does not reach a steady value, even after many timesteps. I tested lower heat generation values -17,000 W/m³(100k lower) and obtained the same trend: the temperature rise was still linear, just at a slower rate. 

Despite multiple trials, the temperature evolution always shows this linear rise, and I am unable to stabilize or match it with the experimental results. I need guidance on resolving this issue.

[AG]

Where is inlet and oulet located ?

What is the flow rate (do you expect this to be forced convection or natural convection - is gravity enabled)?  Is fluid domain created around cell pack a actual flow domain from test (like duct)? 

At the cell walls, I specified a convective heat transfer coefficient of 5 W/m²K (taken from youtube). - which boundary is applied with this setting?