Rheology and thermal conductivity of graphene oxide and coal fly ash hybrid nanofluids for various particle mixture ratios for heat transfer applications: Experimental study

This work presents the synthesis of graphene oxide (GO) and coal fly ash (CFA) nanoparticles (NP) to produce water base mono and hybrid nanofluids (HNF) for different particle mixture ratios of 50:50 and 30:70. X-ray diffraction analysis (XRD), X-ray fluorescence (XRF), dynamic light scattering analysis (DLS), Fourier transform infrared (FTIR), field emission scanning electron microscope (FESEM), Ultraviolet-visible spectroscopy analysis (UV–Vis), and zeta-potential tests were carried out. The non-ionic surfactant polyvinylpyrrolidone (PVP) is added to the nanofluid (NF) to improve stability. The thermal conductivity (TC) and rheology experiments are carried out for the concentration range of 0.1 to 1.0 vol% in the temperature range of 30 to 60 °C. The results show that TC and viscosity (VST) enhancement of GO NF is higher than the studied HNF. The maximum VST enhancement of 177%, 152%, and 113% are observed for GO, and GO/CFA (50:50) and, GO/CFA (30:70), respectively for a concentration of 1 vol% at 30°C relative to water. Based on the obtained data, regression analysis is formed to estimate the TC and VST of the studied HNF. The performance enhancement ratio (PER) results show that GO NF and HNF with a mixture ratio of 30:70 are beneficial for thermal applications at all temperatures, whereas HNF with a mixture ratio of 50:50 is only at 45°C and above.