Synergistic Heat Transfer Enhancement In Backward-Facing Step Geometries Using Hybrid Nanofluids And Passive Geometric Modifications: A Comprehensive Review

Abstract

Backward-facing step (BFS) configurations have emerged as a critical focus in thermal engineering due to their widespread implementation in compact heat exchangers and microscale cooling systems. This review investigates recent developments in thermal enhancement strategies that combine hybrid nanofluids with engineered geometries to improve performance in BFS domains. Emphasis is placed on the thermal and hydrodynamic improvements offered by advanced nanoparticle blends, particularly copper oxide (CuO) and graphene, which demonstrate notable effects on flow recirculation, turbulence intensity, and heat transfer rates. Additionally, this paper examines how geometric elements such as embedded obstacles, modified channel surfaces, and structural deviations affect thermal behaviour based on insights from both computational and experimental literature. Critical metrics like Nusselt number enhancement, pressure drop variation, and thermal resistance reduction are explored in relation to flow conditions and nanoparticle parameters. The review concludes by outlining persistent knowledge gaps and suggesting directions for future research to refine and optimize BFS-based thermal systems using nanofluidic and geometric techniques.