Thermal Characterization of Battery Cold Plates

Abstract

Proper thermal management of Lithium ion batteries is a crucial design consideration in electric vehicles (EV). Liquid cooling is the preferred choice due to its high heat transfer coefficient and compactness. Cold plates used for heat extraction need to maintain the batteries in a temperature range of 20-40C and a temperature uniformity of less than 5C between the batteries. Design and optimization of cold plates require tradeoffs between conflicting requirements including thermal resistance, pressure drop and manufacturing constraints. In case of EV batteries it is also very important to consider the surface temperature uniformity of the cold plate. The main goal of this paper is to thermally characterize the battery cold plates using key design & performance parameters which are relevant to EV. This is expected to help designers develop and optimize solutions quickly that meet their performance targets.A typical battery cold plate was chosen for this study with the dimensions of 250x500x10mm and a uniform heat load of 500W on both sides. The coolant used was a mixture of ethylene glycol and water. A simulation model was created using commercially available CFD tool (FloTHERM). Several design parameters were varied including fluid channel height, number of flow turns, fin pitch and type of coolant to determine their impact on the thermal performance. The thermal performance was characterized in terms of the effectiveness ($\varepsilon$) which is inversely proportional to the thermal resistance of the cold plate and the coolant mass flow rate. The temperature uniformity was calculated using the difference between the maximum and minimum surface temperature of the cold plate $(\Delta {\mathrm {T_{MAX}}})$. The power required for cooling (P) was also calculated as a product of the volumetric flow rate and pressure drop of the cold plate. It was found that increasing the number of flow turns and adding fins resulted in the most significant improvements in $\varepsilon$ and $\Delta {\mathrm {T_{MAX}}}$.