In the present study, 3-D CFD simulations have been performed to examine the hydrothermal performance of a circular-shaped minichannel heat sink. The heat sink is composed of aluminum with dimensions of 40mm × 40mm × 10mm and it is designed for Reynolds numbers less than 1300. A uniform heat flux of 66 KW/m2 is applied to the bottom wall of the heat sink, while other surfaces have been insulated. The finite volume approach was utilized in Ansys-Fluent to solve the system governing equations and associated boundary conditions. Magnetite-water nanofluid has been used as a coolant and examined the variations of mass flow rate and nanofluid concentration on cooling potential. A bronze porous material has been inserted throughout the channel space at various porosity levels. The performances of the heat sink have been further investigated at various channel counts by varying the hydraulic diameter in a manner that the total flow area of the channels remains constant. The results show that the number of channels and their dimensions have a substantial effect on heat transfer efficiency. This investigation reveals that using porous media is very significant relative to nanofluid at any concentration and the maximum augmentation in heat transfer by the incorporation of porous media along with nanofluid is 5.54 times. Moreover, the heat sink’s practical utility is optimized through figures of merit (FOM) and heat transfer efficiency. As a result, the optimum hydrothermal performance of this present study is achieved at six channels with a lower volume flow rate, higher volume fraction of nanofluid, and a lower porosity level.