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چکیده
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In the present study, to improve the rheological behavior and heat transfer characteristics of engine oil, nanolubricants were prepared by suspension of graphene nanoparticles (GNPs) (2–8nm) and tungsten trioxide (WO3 ) (23–65nm) in working fluid using a two-step approach. The nanoengine 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 nanofluid viscosity increased with the increase of the weight fraction of NPs, and the same concentration decreased with the increase in shear rate. Three theoretical models have been developed for predicting the rheological behavior of nanofluids. The curve fitting of the shear stress–shear rate shows that the relationship between them is linear at all weight fractions of NPs, so the nanofluids have Newtonian behavior. The effects of Reynolds number and NPs weight fraction (0.2, 0.4, 0.8, and 1.2wt.%) 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 concerning 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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