Improving the thermal conductivity of water by adding mono & hybrid nano-additives containing graphene and silica: A comparative experimental study

Effect of addition and hybridization of Graphene (G) and Silica (SiO2) nanoparticles on thermal conductivity of water, was experimentally studied. Initially, XRD, FTIR and FESEM tests were performed to specify phase and structural analysis and microstructural-observation of nano-materials. After that, nano-materials were dispersed and homogenized in distilled water by magnetic stirrer and ultrasonic vibrator, using the two-step method. The stability of graphene and silica nanoparticles in the base fluid at different pH values was examined. Thermal conductivity of three types of nanofluids, G/Water, SiO2/Water and G-SiO2/Water, at different volume fractions (phi) of 0.05-1% and temperature (T) range of 25-50 degrees C was measured. For predicting the thermal conductivity of G-SiO2/water hybrid-nanofluid, a two-variable correlation with R-Squared = 0.99 was extracted from experimental data by curve fitting method. The most and the least thermal conductivity enhancement attributed to G/water and SiO2/water mono-nanofluids respectively; while thermal conductivity enhancement between these two values and closer to the greater value associated with G-SiO2/water hybrid-nanofluid. By comparing the thermal conductivity results of the three present types of nanofluids, G-SiO2/Water hybrid-nanofluid would be a good choice as a high thermal and cost-effective nanofluid for thermal equipment.