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Abstract
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In the present study, to improve the rheological behavior and heat transfer characteristics of engine oil, nano lubricants were prepared by suspension of graphene nanoparticles (GNPs) (2-8 nm) and tungsten trioxide (WO3) (23-65 nm) in working fluid using a two-step approach. The nano engine oil had good stability and dispersibility without agglomeration phenomenon. The influences of adding NPs to the base fluid on the dynamic viscosity and shear stress for different shear rates at room temperature were studied. The viscosity of nanofluid increased with the increase of the weight fraction of NPs, and with the same concentration decreased with the increase of shear rate. Three theoretical models have been developed for predicting the rheological behavior of nanofluids. The curve fitting of shear stress-shear rate show that the relationship between them is linear at all weight fraction of NPs and so the nanofluids have Newtonian behavior. The effects of Reynolds number and NPs weight fraction (0.2, 0.4, 0.8, 1.2 wt.%) on the convective heat transfer coefficient and pressure drop of GNPs-WO3/engine oil hybrid nanofluids in a horizontal circular tube under laminar flow condition were investigated experimentally. The enhancement of convective heat transfer coefficient and Nusselt number were found to increase with respect to NPs weight fraction and Reynolds number up to 140.8% and 95.2%, respectively. According to the features expressed for the proposed hybrid nanofluid, it can be applied in different areas of lubrication and heat transfer.
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