Figures-of-Merit Analysis Using the Thermophysical Properties of Water and Ethylene Glycol Based Reduced Graphene Oxide/Nanodiamond Hybrid Nanofluids

The water and ethylene glycol based stable rGO/nanodiamond hybrid nanofluids were prepared and used for thermophysical properties analysis. The thermophysical properties were measured experimentally at various particle loadings from 0.2% to 1.0% and various temperatures ranging from 20 to 60 °C. From the measured thermophysical properties the figures-of-merit were analyzed by assuming constant heat flux and turbulent boundary conditions by using different models, and also by assuming the hybrid nanofluids flows through a tube. Results indicate that the thermal conductivity of water and ethylene glycol based hybrid nanofluids at Φ = 1.0% vol. is enhanced about 27.87% and 18.8% at 60 °C; viscosity of water and ethylene glycol based hybrid nanofluids at Φ = 1.0% vol. is also enhanced by 72.15% and 86.62% compared to their base fluids at 20 °C. The density is also increased with an increase of particle loadings, whereas, the specific heat is decreased with a rise of particle loadings. Experimental thermophysical properties are fitted into regression equations by using multi linear regression method. The figures-of-merit of all the prepared hybrid nanofluids show its value is less than one under the used particle loadings and temperatures.