Critical thickness of nano-enhanced RT-42 paraffin based battery thermal management system for electric vehicles: A numerical study

Use of electric vehicles has increased worldwide. Lithium Ion (Li-Ion) batteries are widely used to power them due to their high energy density and low self-discharge rates as compared to other conventional batteries such as lead acid. But at 3C discharge rates (where 3C means 3 times the rated Ah capacity of the battery cell), there is a sharp rise in temperature which impacts battery cell performance. After temperature exceeding 50 °C, the Li-Ion battery cells become unstable and catch fire and thus, its thermal management became a priority. Battery thermal management system (BTMS) aims to control battery cell temperature within operating limits at high discharge rates and ambient temperatures. BTMS utilizes either a fluid medium to carry away heat or working material in the form of Phase Change Material (PCM). In the present numerical investigation RT-42 paraffin is used as working material to control battery temperatures. In this investigation the performance of RT-42 paraffin for different thicknesses ranging from 1 mm to 7 mm around the battery cell was used to control battery temperature effectively. It is observed that up to 4 mm thickness of RT-42 paraffin gain in controlling the temperature is maximum. But low thermal conductivity of pure RT-42 impacts on its heat transfer performance. Therefore investigation of performance of Al2O3/RT-42 paraffin nano PCM (NePCM) with percentage weight fractions of 0.5, 1, 2, and 5 at critical thickness 4 mm was carried out. NePCM was able to maintain the maximum battery temperature 42.77 °C and remains in partially liquefied state at the end of discharge cycle of 1200 s.