Numerical Investigation of Thermal Performance of MiniChannel Heat Sinks with Different Geometries Using Al₂O₃Water Nanofluid

A numerical investigation of five mini-channel heat sink geometries circular (0.8 mm, 1.0 mm), rectangular (0.8 mm, 1.5 mm) and converging-diverging (0.8 mm throat) cooled by Al₂O₃–water nanofluid was carried out over Re = 300–1800 and φ = 0–0.09% under a constant 50,000 W/m² base heat flux. The main conclusions are: ●       Reynolds number is the dominant design variable: raising Re from 300 to 1800 cut outlet temperature by up to 151.6 K and shrank wall temperature non-uniformity more than 3-fold in the circular 0.8 mm channel, with similar trends in every other geometry. ●        A dilute Al₂O₃ nanofluid concentration of φ ≈ 0.01% consistently gave the best thermal performance across all five geometries; beyond this, rising effective viscosity offset the conductivity gain and outlet temperature increased again, so nanofluid loading should be treated as an optimisation variable rather than maximised. ●       Channel geometry has a first-order effect independent of nanofluid concentration: the converging-diverging channel and the 1.5 mm rectangular  channel  consistently outperformed both circular channels, combining the lowest outlet temperature with the most uniform wall temperature at Re = 300. ●       Increasing circular channel diameter from 0.8 mm to 1.0 mm improved performance at every Re tested (with one anomaly at Re = 1800, pure water), showing that a larger flow area and hence higher mass flow rate at fixed Re can outweigh the loss in convective coefficient from a larger hydraulic diameter. ●       For compact electronic cooling applications, the converging-diverging channel with Al₂O₃–water nanofluid at φ ≈ 0.01% is recommended as the most effective combination identified in this study, offering the best balance of low base temperature and thermal uniformity. Future work should extend this comparison to a wider range of nanoparticle materials and hybrid nanofluids, include pressure-drop and pumping-power optimisation alongside thermal performance, and validate the numerical predictions against experimental data for the converging-diverging geometry.

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