In the present study, the thermofluid characteristics of a water and nanofluid-cooled micropin-fin heat sink have been evaluated by implementing a two-phase Eulerian-lagrangian model. The nanofluid consisted of an aqueous suspension of the spherical-shaped alumina nanopartides with the particle volume fraction (phi) ranging from 0.25% to 1%. The analysis has been performed by considering a heat sink comprising the staggered arrangement of 72 micropin-fins of the circular cross-section without tip clearance. A constant heat flux of 300 kW/m(2) was subjected at the base of the heat sink, whilst the utilised pressure drop (Delta P) across the heat sink was limited to Delta P<3000Pa. Heat transfer and fluid flow parameters were evaluated in terms of the local heat transfer coefficient, the enhancement ratio of the average convective heat transfer coefficient, thermal resistance and volume flow rate through the heat sink. Additionally, the temperature contours and flow streamlines across the heat sink elaborated the temperature distribution and flow attributes. Results indicated that under identical AP conditions, replacing water coolants with nanofluids optimised the thermal performance of the heat sink with a perceptible margin at the higher particle loadings. At the optimal pressure drop and particle concentration, nanoparticle dispersion into the hosting fluid demonstrated a maximum of 16% enhancement in the average heat transfer coefficient. (C) 2019 Elsevier B.V. All rights reserved.