Graphene functionalized nano-encapsulated composite phase change material based nanofluid for battery cooling: An experimental investigation

The graphene-nano encapsulated composite phase change material (GnePCM) based nanofluid holds great potential as a coolant for batteries in electric vehicles. The current work focuses on the synthesis and study of the cooling performance of GnePCM-based nanofluid. Few layered graphene (FLG) was synthesized via the liquid phase exfoliation method. Mini-emulsion polymerization was adopted to encapsulate composite PCM (octadecane: paraffin wax) within polystyrene shell and distribute these nanoballs across the graphene flakes of FLG to obtain GnePCM. Differential Scanning Calorimetry (DSC) was used to optimize the composition of composite PCM based on the melting range and latent heat. GnePCM was characterized by Scanning Electron Microscope (SEM), Transmission Electron Microscopy (TEM), DSC, Fourier Transform Infrared (FTIR) spectroscopy, and Raman Spectroscopy. Nanofluid was made by mixing GnePCM slurry with the base fluid (ethylene glycol- water mixture) and its thermo-physical properties were estimated. The analysis of thermal conductivity and specific heat capacity showed a 14.7 % and 56 % increase for the nanofluid compared to the base fluid. The optimal concentration of nanofluid for maximum stability was 10 % v/v based on zeta potential measurements. The heat transfer studies and pressure drop studies were conducted on a set of 10 cylindrical heaters, mimicking a 18,650 battery cell pack. The nanofluid could potentially achieve a maximum reduction of 5 degrees C in average surface temperatures of the cells as compared to the base fluid. The enhanced cooling efficiency of nanofluid could be related to the increased thermal conductivity and heat capacity of GnePCM, as well as the absorption of latent heat during its melting process. Enhancement in heat transfer parameters was found to be more prominent at lower flow rates for the nanofluids. The results reveal that the flow rate and power input play a significant role in the cooling performance of the nanofluid. Due to the increased viscosity of the nanofluid, a slight increase in the pressure drop and pumping power was observed at higher flow rates, as compared to base fluid.