Preparation and characterization of aluminium oxide nanofluids, polyurethane nanocapsules nanofluids and hybrid nanofluids

anofluids attract the attention of researchers due to their unique physical and chemical properties. These physical and chemical properties, which vary with the morphology, size, and chemical nature of the nanoparticles used, cause nanofluids to exhibit unique characteristics. Nanofluids prepared using various basic fluids are widely used in heat transfer applications due to their increased heat conduction coefficients and convection coefficients. The high cooling rates, low pumping power, and abrasion resistance they provide are used in applications in many fields of industry, such as manufacturing, energy, transportation, and electronics. In summary, nanofluids obtained by dispersing nanoparticles in a base fluid are preferred for heat transfer enhancement due to their high heat transfer coefficients. The idea of using FDMs for thermal energy storage usually involves a phase change between a solid and a liquid phase to utilize latent heat. The use of latent energy storage systems using phase-change materials is the most efficient way to store thermal energy and has the advantages of the isothermal nature of the storage processes and high energy density. So, in this study, nanoscale capsules were made by nano-encapsulating a phase change agent. Pure water was used as the base fluid and nanocapsules with a polyurethane shell containing Al2O3 and a phase change agent as nanoparticles were used to make mono and hybrid nanofluids. The effect of the amount of surfactant on the stability of the nanofluids was investigated. The thermal conductivity and viscosity values of the nanofluids were determined. The volumetric solid ratios of the nanofluids were selected as 0.01%, 0.05%, and 0.1%. The amount of surfactant was determined to be 0.05g, 0.1 g, and 0.15g. Thermal conductivities were measured with a KD2 Pro thermal conductivity meter. Thermal conductivity values were found in the range of 0.604 W/m.K.–0.628 W/m.K. for Al2O3/water nanofluids, 0.540 W/m.K.–0.596 W/m.K. for polyurethane nanocapsule/water nanofluids, and 0.604 W/m.K.–0.609 W/m.K. for hybrid nanofluids. Viscosities were determined using a Vibro brand viscometer. Viscosity values were obtained in the range of 0.97 cp–1.09 cp for Al2O3/water nanofluids, 0.94 cp–1.07 cp for polyurethane nanocapsules/water nanofluids, and 1 cp–1.03 cp for hybrid nanofluids. All measurements were performed at room temperature. In general, it was observed that thermal conductivity and viscosity values increased as the amount of solid and surfactant increased.