Thermal Performance of Poly Alpha Olefin Nanofluid with Spherical and Non-spherical Nanoparticles

Research on nanofluids has been undertaken for several years because of the reported enhancements of thermal properties such as thermal conductivity and enhanced heat transfer performance in laminar flow. Nanofluid is the fluid where nanoparticles are dispersed in a base fluid. Thermal conductivity and viscosity are considered to be the most prominent factors in the efficient use of nanofluids. A change in thermal conductivity and viscosity also changes the convective heat transfer coefficient. Nanoparticles can be metallic or non-metallic and also can have different shapes. In this study, Poly-Alpha-Olefin (PAO) has been used as a base fluid with Alumina (Al2O3) nanoparticles. Poly-Alpha-Olefin is commonly used for engine lubrication in military applications and cooling in electronic and industrial devices. Several nanofluid samples were made by METSS Corp. in Ohio, USA using different dispersants, different base fluids and different morphology of alumina nanoparticles. The mass fraction of nanoparticles is from 2.5 to 20 percent. The thermal properties of each sample such as thermal conductivity and viscosity have been measured. Thermal conductivity of nanofluids and pure base fluids were both measured and the thermal conductivity enhancement has been calculated. Also, the heat transfer coefficient has been determined for laminar flow under constant heat flux conditions.

Results indicate that all the tested nanofluids and base fluid samples show a Newtonian behavior. Among the nanofluid samples, NF-048, which contains non-spherical Alumina nanoparticles exhibits the greatest thermal conductivity enhancement when compared to pure PAO. Heat transfer tests were conducted with pure PAO and NF-048, and an enhancement in convective heat transfer coefficient was observed. The thermal conductivity of NF-048 increases with temperature, which is consistent with heat transfer results. Furthermore, the percentage enhancement in convective heat transfer coefficient was shown to increase non-linearly with the axial distance in the heat transfer section. NF-048 exhibits a lower Re (Reynolds number)*Ra (Rayleigh number) than pure PAO under laminar flow constant heat flux conditions indicating that nanoparticle morphology and composition are the two main factors responsible for convective heat transfer enhancement at low Reynolds number.