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This study presents the stability, thermal conductivity and rheological properties of Graphene (GR) and Multi-wall carbon nanotube (MWCNT) in SUNISO SL68 Oil with different surfactants. Cetrimonium bromide (CTAB), Sodium Dodecylbenzene Sulfonate (SDBS), and Sorbitan monooleate (SPAN-80) are used as a surfactant. Zeta potential measurement was used to identify the agglomeration tendency of the samples. Visual observation, aided by an LED backlight, was used to investigate the sedimentation tendency of the samples. Thermal conductivity was measured to determine conductivity improvements of a nanolubricant with additive surfactants. Lastly, a cone and plate were used to measure the viscosity of the samples at different shear rates and temperatures. Zeta potential results were matched with visual observation results and CTAB is shown to be a better surfactant for both GR and MWCNT. Thermal conductivity analysis shows no significant improvement within the different surfactants, however, between 2% and 7% improvement is recorded when comparing nanolubricant to pure oil. A non-Newtonian fluid behaviour, specifically, Shear-thinning flow behaviour is observed in MWCNT nanolubricant samples, unlike the pure oil that shows a Newtonian fluid behaviour.

Engineering applications and energy-saving techniques have significantly improved by the new nanoparticle technologies. Many researchers revealed that by using nanoparticles in their work results have been improved. In the context of that, graphene nanoparticles have advantages and cannot be underestimated in this new revolution. Besides, it is hard to maintain the dispersion of the nanoparticles in the medium. The aim of this experiment is to evaluate the thermal properties and the stability of graphene nanoparticles in full synthetic lubricant oil for securing its durability and efficiency as nanolubricant for air conditioning compressors. The volume fractions of the graphene nanoparticles considered in the experiment are 0.05, 0.1, 0.2, and 0.3 volume fraction percentage of graphene (vol.%). A two-step method implemented to acquire the nanolubricant. Ultrasonic vibrator used to disperse graphene nanoparticles in the lubricant oil for 40 min. Visual inspection shows sedimentation started after 1 day from sonication process and after 14 days sedimentation almost stopped. Zeta potential analyser were used to measure the stability and the dispersion of the graphene nanoparticles in the lubricant oil. Sample 0.05 vol.% shows poor stability at zeta potential -7 mV. However, the samples 0.1, 0.2, and 0.3 vol.% shows good stability at zeta potential around -40 mV. Thermal conductivity analyser utilized to evaluate the thermal conductivity alteration. The sample 0.3 vol.% recorded the highest thermal conductivity with 26% improvement. The addition of nanoparticles increases the viscosity of the lubricant for 7 % for sample 0.3 vol.%. It is observed that the nanoparticles sedimentation occurred after 14 days. The thermal conductivity increased with slight change in viscosity.