Transient Heat Transfer of 42V Ni-MH Batteries for an HEV Application

While a Ni-MH battery has good performance properties, such as a high power density and no memory effect, it needs a powerful thermal management system to maintain within the required narrow thermal operating range for the 42V HEV applications. Inappropriate battery temperatures result in degradation of the battery performance and life. For the battery cooling system, air is blown into the battery pack. The exhaust is then vented outside due to potential safety issues with battery emissions. This cooling strategy can significantly impact fuel economy and cabin climate control. This is particularly true when the battery is experiencing frequent charge and discharge of high-depths in extreme hot or cold weather conditions.

To optimize performance and life of HEV traction batteries, the battery cooling design must keep the battery operation temperature below a maximum value and uniform across the battery cells. For the cooling analysis of the battery system, a lumped thermal/fluid model was built as a good approximation of a 3-D CFD modeling. For better battery cooling, several options were examined and the best option was chosen based on the thermal analysis. This paper presents the transient heat transfer analysis of 42V Ni-MH batteries and the results of the battery cooling analysis with recommendations for improved cooling performance.