I am trying to model a battery pack of Li-ion cylindrical cells. I read somewhere that heat transfers significantly along the plane of electrodes. means in the cylindrical cell, more heat transfer will occur in the axial direction. But in the image, which is from a research paper on designing BTMS, they didn't simulate the top and bottom parts of the cell, saying that heat transfer will occur from the side of cells. Can anyone please explain what is the correct thing?
They probably assessed, theoretically, the approximate heat transfer through the top and bottom to see if it was negligible or not.
After determining it was negligible, they likely used the adiabatic wall condition to simplify the simulation.
I think they used it only as a simplification of their model. Considering the top and bottom in your computational domain results in a more accurate solution (at a higher computation cost, which may not be that significant!), so regarding your question about the correctness, considering a larger computational domain enclosing top and bottom is more correct.
You have the difference between the practical behaviour of a battery pack the the theoretical behaviour, specified accurately. Yes, you have to take into account heat loss from the ends of each cell in the theoretical case to get an accurate answer. But consider this: The ends of the cell will not be so readily exposed to the cooling medium as the sides, and the areas are much smaller for conventional cylindrical cells. Additionally the ends of the cells are either close to the pack wall or adjacent to another layer of cells. In the second case the temperature difference between the ends will tend to zero so there won't be any substantial heat flow. So, for practical purposes, it can be neglected. If the pack is stable with the end heat loss neglected, it will certainly be stable with the end loss taken into account.
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