The present research aims to enhance heat transfer in straight and wavy profile heat sinks using the same length and hydraulic diameter with different microchannel geometries (triangular, rectangular, trapezoidal, semi-circular, and circular) for uses in electronics, inkjet printing, high heat flux cooling of lasers, and other domains. The nanofluid employed is water/aluminum oxide (water/Al2O3), and the flow regime is laminar. The range of Reynolds number (Re) in this study was 220 � Re � 550, and the concentrations of nanoparticle Al2O3 with Heavy Water (2H2O) were 1.2 volume. This investigation uses 3-dimensional Computational Fluid Dynamics (CFD) simulation software to investigate the heat transfer characteristics of several cross-sectioned microchannels. The numerical investigation utilizes the finite volume approach, and the CFD analysis is validated with accessible literature with different wavy profiles. According to the CFD simulation results, the microchannel with a circular cross-section has the highest heat transfer performance (up to 18 ) among the other cross-sections. The circular cross-section microchannel seemed to have the most significant increase in coolant temperature (by 9-22 ). The analysis outcomes prove that the microchannel with a circular cross-section has the highest performance for heat transfer; the triangular channel has the lowest performance under the same geometric parameters and boundary conditions. So, it is suggested that a circular microchannel can be used for a heat-carrying capacity of 150 W/cm2, a hydraulic diameter of 500 μm, and a Reynolds number equal to 500. © 2023 Walter de Gruyter GmbH, Berlin/Boston.