This study experimentally investigates the thermo-hydraulic performance of plain and oval-shaped mini-channel heat sinks using DI water and hBN nanofluids at concentrations of 0.05% and 0.10%. The influence of Reynolds number, channel geometry, and nanoparticle concentration on Nusselt number, heat-transfer coefficient, pressure drop, friction factor, and pumping power was quantified. Results showed that the oval mini-channel with 0.10% hBN nanofluid produced the highest thermal enhancement, achieving a 220% increase in Nusselt number and a 240% rise in heat-transfer coefficient at Re 900 compared to plain DI water. Increasing nanoparticle concentration from 0.05% to 0.10% further improved the Nusselt number by 35%, indicating strong particle-driven thermal enhancement. Geometry effects alone contributed an additional 20% improvement, demonstrating the significance of flow restructuring via oval cross-sections. Pressure-drop penalties remained moderate, increasing by 11.03% for the oval channel with 0.10% hBN and 7.40% for DI water relative to plain channels. Overall, the combined effects of optimized channel geometry and hBN nano fluid significantly improved convective heat transfer with acceptable hydraulic losses, establishing oval mini-channels as a superior design for compact high-heat-flux thermal management systems.