Computational study of thermofluidic characteristics of Al2O3-Cu hybrid nanofluids in backward facing step channel with varying step angles

Backward-Facing Step (BFS) channels are frequently utilized in technical implementation due to their ability to model intricate fluid flow patterns, such as recirculation zones, which have significant impacts on thermal exchange rates. This research investigates the thermal and heating efficiency of Al₂O₃-Cu hybrid nanofluids in a BFS channel, focusing on the effects of varying step angles and Reynolds numbers (Re) on thermal efficiency. ANSYS Fluent (2021 R2) was used to analyze Al₂O₃-Cu nanofluids across Reynolds numbers (500-800), step angles (70°, 75°, 80°, and 85°), and particle volumes (1%-4%) applying the finite volume method. The results demonstrate that as the Reynolds number increases, the Nusselt number rises by an average of 18.505 %. In contrast, varying the step angle results in an average increase of 4.94 %. It is also observed that an increase in volume fraction of nanoparticles enhances the Nusselt number due to the superior thermal conductivity of the Al₂O₃-Cu nanofluid. Additionally, a positive correlation between step angle, skin friction coefficient, and pressure drop was observed.