Analysis of heat transfer performance and thermo-hydraulic characteristics of graphene nanofluids: impact of sedimentation effects

Abstract

This study investigates the heat transfer performance and thermo-hydraulic characteristics of nanofluids containing graphene nanoparticles in a water and ethylene glycol mixture. Results show that both nanofluid samples, with concentrations of 0.15% and 0.10% by volume, experience increased heat transfer coefficients (h) compared to the base fluid under various operating conditions, with average reductions of approximately 21% and 26%, respectively. Additionally, the nanofluids exhibit higher friction losses and pressure drops compared to the base fluid. The friction factor and head loss increased by 8.7% and 7.7% for the 0.15% concentration sample and 12.7% and 12.4% for the 0.10% concentration sample. These findings indicate that the thermo-hydraulic performance of the nanofluids is unsatisfactory, offering limited advantages over the base fluid. Surprisingly, the sedimentation of nanoparticles in the test section leads to unexpected results. Contrary to typical observations, the higher concentration sample shows a lower head loss. This discrepancy is attributed to nanoparticle sedimentation, increasing friction factors, and pressure drops. The study also examines the thermal conductivity and viscosity of the nanofluids. It is found that even at low concentrations, graphene nanofluids exhibit higher thermal conductivity than the base fluid. The dynamic viscosity slightly increases with concentration, aligning well with theoretical models. Further research is needed to optimize nanofluid performance and address these issues in practical applications.