Batteries used to propel automobiles today have a lot more capacity than 16 years ago when the lithium based batteries were discovered. Lithium-ion batteries are frequently used in the automobile industry, however, lithium based batteries are very sensitive to the charging level and operating temperature. So it is important to have a cooling and heating system to ensure that the batteries stay within a limited operating range in order to optimize their usage and avoid thermal runaway.

A battery pack with implemented cooling system was identified through data and STEP-files provided by NEVS, and COMSOL Multiphysics were used to simulate the system in order to observe the thermal dissipation. Simplifications were done to be able to easily mesh the model, shorten the computation time and also because of the limitation of knowledge in more complex areas in order to perform the simulation. The refrigerant used was EGL (ethylene glycol), a commonly used refrigerant in the automotive industry, and the flow type of the refrigerant was identified through the use of the dimensionless quantity Reynolds number. After showing that the flow is laminar, a non-slip boundary condition was defined for flow in the simulation meaning the refrigerant will have zero velocity at a solid boundary.

The heat generation of the battery cells was identified through calculations of the joule heating and dissipated energy in the electrode over potentials. The velocity, flow and heat transfer of the refrigerant can differ depending on the size and form of the cooling pipes, so different pipe profiles were experimented with to identify an optimal profile. Results of the simulation using the batteries maximum current (given by a curve illustrating the amperage passing through a battery cell during a test drive) showed that the maximum temperature by far surpassed the limited operating range.

After analyzing the given system, it was observed that the battery pack received a sufficient amount of cooling to keep the temperature between the operational parameters. However, the simulations showed that the modules that were connected in series didn’t have as optimal cooling as the modules connected in parallel. Because as the refrigerant passes through the first module it transfers heat from the module to the refrigerant (which is the definition of cooling) and thereby have a higher temperature as it passes through the second module than the first one, giving the second module a higher overall temperature. Because of the higher temperature in the second module, it is also more prone to aging. The analysis of the different profiles showed that even though there is a difference in velocity as the refrigerant passes through the cooling pipes, the heat dissipation showed a low difference. Giving only a difference in temperature of 3°C.