Enhancing the thermophysical properties of PAG lubricant using graphene nano-sheets

One of the most attractive methods to improve the thermo physical and heat transfer properties of conventional coolants and lubricants is the use of nanoparticles in it. Nanofluids are stable colloidal suspensions of nanoparticles and base fluids. The nanofluids exhibit superior thermal performance compared to conventional heat transfer fluids and this leads to the best hope for lubricants based nanofluids as well. Nanolubricant is a new class of lubricant produced by dispersing nano-sized particles of metals, metal oxides, carbon and its allotropes into conventional lubricating oils. In the present study, experiments were conducted to measure the thermophysical and rheological properties of polyalkyleneglycol (PAG) refrigerant compressor oil suspended with graphene nano-sheets. The effect of particle concentration and temperature on thermal conductivity and viscosity of nanolubricant were elucidated. The volume fraction is varied from 0.05 to 0.8% and the temperature range is from 15°C to 85°C. The rheological properties have been investigated at various shear rates, particle concentrations, and temperatures. Furthermore, a correlation is proposed to predict the thermal conductivity of Graphene-PAG nanolubricant. The results revealed that the thermal conductivity and viscosity of the nanolubricant is strongly depends on the volume fraction and temperature. The nanolubricant exhibits higher thermal conductivity and viscosity compared to the PAG oil. Unlike in the case of pure lubricant, the shear rate has a crucial impact on the behavior of nanolubricant. Interestingly, the pure lubricant, which is a Newtonian fluid, is transformed into non-Newtonian when nanoparticles are appended with it. From the studies, it was observed that the nanolubricant having graphene particle concentration of 0.05% is optimum for refrigeration application. (paper)