Thermal performance enhancement of microchannel heat sinks under an oblique magnetic field for electronic cooling applications

Efficient thermal management of microchannel heat sinks (MCHSs) is essential for high-power electronic systems. This numerical study examines the influence of a magnetic field with variable angles on the flow structure, heat transfer, and hydraulic performance of a rectangular MCHS cooled by Al₂O₃-water nanofluid. The effects of the magnetic field angle ( 0^∘ ≤ α ≤ 90^∘ ), Hartmann number ( 0≤ Ha≤ 40 ), and Reynolds number ( 250≤ Re≤ 2000 ) are systematically analyzed and compared with the transverse and no-field cases. The performance evaluation criterion (PEC) is used to quantify the trade-off between heat transfer enhancement and pressure losses. Results indicate that, compared to the no-magnetic field case, an oblique magnetic field at α =45^∘ yields the maximum enhancement in the mean heat transfer coefficient (up to 86%) and reduces thermal resistance by 52%; however, this improvement is accompanied by a notable increase in pumping power at higher Ha . The conventional transverse configuration ( α = 90^∘ ) consistently yields PEC values below unity across the examined Ha and Re ranges, highlighting its limited effectiveness. In contrast, an oblique magnetic field at α = 15^∘ yields the highest PEC, exceeding the α = 90^∘ and α = 45^∘ cases by 70.9% and 20.2%, respectively, highlighting the dominant role of magnetic field orientation in governing MCHS performance.