Numerical and experimental investigation on the melting heat transfer of nanographene-enhanced phase change material composites for thermal energy storage applications

Abstract

Phase change materials (PCMs) low thermal conductivity limit the performance of latent heat thermal energy storage systems. To enhance the thermal conductivity of the heat storage medium, highly conductive additives could be added to the base PCM. Hence, the present work aims to perform numerical and experimental investigations on the melting heat transfer of the PCM (OM 65) loaded with highly conductive graphene nanoparticles (GNPs) at weight fractions of 1%, 2%, and 3%. Based on the aforementioned weight fractions of graphene nanoparticles in the PCM, the nanographene-enhanced PCM (NPCM) composites are named NPCM 1, NPCM 2, and NPCM 3 respectively. The temperature-dependant thermal conductivity and dynamic viscosity were measured. A transient heat transfer during the melting of the PCM and NPCMs in a two-dimensional rectangular domain heated from the bottom-up configuration was considered for the numerical study. The base temperature was maintained at a constant temperature (Th = 70 °C), and the remaining walls are adiabatic. The transient variation of liquid fraction and temperature were presented. The PCM and NPCMs are experimentally studied using the proposed three-dimensional rectangular test section with twenty-four thermocouples and a temperature logger. Compared to the base PCM, the reduction in melting time from the numerical and experimental study was 37.5% and 36.5% for NPCM 3. It was evident that adding GNPs to PCM enhances its thermal conductivity. However, the higher concentration of GNPs could drastically increase the NPCMs viscosity, as well as cause agglomeration and sedimentation of GNPs during melting. Therefore, adding a maximum of 3wt% GNPs into the PCM was recommended.