An experimental methodology on the determination of stability and characterization of nanofluids

In this thesis, an experimental methodology on the determination of the stability and characterization of nanofluids is presented. With 77 nm diameter CuO nanoparticles, CuO–Deionized Water and CuO–Ethylene Glycol nanofluids were prepared in volume fractions of 0.01, 0.05, and 0.1%. Nanofluids and base fluids were heated to 60 °C and their cooling from 60 °C to ambient temperature was photographed over time with a thermal camera. Deionized Water cooled to ambient temperature in the 207th minute, and CuO–Deionized Water nanofluids with 0.01, 0.05 and 0.1% volume fractions cooled simultaneously in the 180th minute. Ethylene Glycol cooled to ambient temperature in the 130th minute, and CuO–Ethylene Glycol nanofluids cooled to ambient temperature at the same time and in the 90th minute. Ambient temperatures were recorded as 25.5 °C for Deionized Water and CuO–Deionized Water nanofluids and 30.1 °C for Ethylene Glycol and CuO–Ethylene Glycol nanofluids. It was observed that CuO nanoparticles significantly reduced the cooling durations of the fluids. The stability of CuO–Deionized Water nanofluids with volume fractions of 0.01%, 0.05%, and 0.1% was determined as 190 minutes, using the sedimentation photograph capturing method. Viscosities of the nanofluids were measured over time, and the results indicated stability durations of 50, 150, and 200 minutes for nanofluids with volume fractions of 0.01%, 0.05%, and 0.1% in CuO–Deionized Water, respectively. The stability periods for CuO–Ethylene Glycol nanofluids with 0.01%, 0.05%, and 0.1% volume fractions were determined to be 7 days, 10 days, and 15 days, respectively. The end of stability was attributed to the time when the nanofluid viscosity equaled that of the base fluid. This new method has proven that stability durations and sedimentation behaviors can be determined sensitively and accurately by measuring a thermophysical property. Thermal conductivities of nanofluids were calculated using theoretical equations and experimental results. Sedimentation velocities were calculated, results showed that increasing volume fractions decreased the sedimentation velocity, confirming the stability times determined by viscosity measurements. Likewise, another observation revealed that the sedimentation velocities of CuO–Deionized Water nanofluids were approximately 10 times higher than those of CuO–Ethylene Glycol nanofluids. As a result, it has been proven that stability and sedimentation behavior can be determined with greater precision and accuracy by measuring viscosity. Furthermore, cooling measurements with viscosity measurements are going to be assessed to satisfy the stability determination as a future work.