The tribological investigation was performed to seek the role of graphene nanoplatelets (GNPs) in enhancing the physico-tribological properties of mahua oil. The flashpoint, fire point, viscosity, wear preventive characteristics (WPC) and extreme pressure characteristics (EPC) were conducted following the governing standards. A substantial decrement of 17% in the coefficient of friction, 15.15% in wear scar diameter was observed upon blending the 0.25 wt.% GNPs with mahua oil. The WPC morphology on the steel balls portrayed the micro tracks. The EPC investigation presented 1 wt. % GNPs blended mahua oil with the augmented outcome of 7.7% and this was portrayed to be the best GNPs loading in weld load perspective. However, at 0.1 wt.% of GNPs loading was identified as the best loading with a wear point of view. The morphology of EPC revealed severe abrasion and steel balls were exposed to very high temperatures and have undergone metal squeeze out from the contact surface. This article also discusses the different wear regimes and corresponding wear phenomena in four-ball tribology testing with the aid of micrographs. RECEIVED

Settling or hydrodynamic entrance lengths have been determined for turbulent flow of air in three smooth concentric annuli of diameter ratios 0.306, 0.527, and 0.842. Both square-edged and bellmouth entrances were investigated for Reynolds number ranging from 7000–47,500. Flow separation caused by the abrupt change in area of the square-edged entrance resulted in skewed (distorted) velocity profiles near the entrance. This skewness was modified further downstream and finally fully developed velocity profiles were established. The settling lengths for the annuli with the square-edged entrances were between 25 and 35 dia. With the bellmouth entrance, the velocity profile developed conventionally from the nearly flat profile at the inlet. The settling lengths for the bellmouth entrances were about 10–15 equivalent diameters more than those for the square-edged entrances.

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