Thermal-hydraulic performance enhancement in a microchannel using an active oscillating vortex generator and nanofluids

Enhancing heat transfer in microchannel cooling systems requires a careful balance between flow disturbance and hydraulic penalty. This numerical study examines the combined effects of active vortex excitation and nanofluid addition in a locally heated microchannel. An oscillating circular vortex generator is employed, and an Al₂O₃-water nanofluid is modeled using Buongiorno’s two-phase formulation. The influences of oscillation amplitude ratio ( A ) and nanofluid volume fraction (NVF, φ ) on flow structure, thermal efficiency (Φ T ), mechanical penalty (Φ M ), and the resulting thermal performance factor (TPF) are examined. The results show that active vortex generates sustained vortical structures that effectively disrupt the thermal boundary layer, leading to a pronounced increase in Φ T compared with both the pure channel (No VG) and fixed vortex generator (Fixed VG). Increasing the oscillation amplitude ratio enhances Φ T , but also raises Φ M . At φ = 0.0%, the TPF ranking varies with amplitude, with No VG yielding the highest TPF at A ≤ 0.3, followed by Active VG and Fixed VG, while at A ≥ 0.3 the Active VG provides the best overall performance. The introduction of nanofluids further amplifies thermal performance, with a maximum Φ T enhancement of 60.60% observed at φ = 6.0%. When combined with active vortex excitation, the overall TPF is improved relative to the No VG case, with the highest value observed at A = 0.4 and φ = 5.4%. These findings confirm that active vortex control dominates heat transfer enhancement, while nanofluids provide an additional performance margin when appropriately coupled with oscillatory flow modulation.