ABSTRACT

This is a general overview of the recent advances in the area of the heat transfer improvement in horizontal annular passages through nanofluids with an emphasis on hybrid and mono-nanoparticle suspensions, as well as on several passive methods of enhancement. The review has summarized the results of ten recent research papers (2023-2025) that discuss various nanofluid configurations (e.g., GnP/MWCN, Alumina/ Grapheme Oxide, f-MWCNT-Fe2O3), passage geometries (annular, doublepipe, corrugated), and how it can be enhanced (perforated fins, twisted tapes, magnetic fields, and the effect of nanoparticle sizes). It is suggested by the analysis that hybrid nanofluids can provide the best thermal performance, and that the geometric modifications, including noncircular inner rods and perforated fins, have a strong effect to maximize the convective heat transfer coaction. Some of the key findings point out those improvements can be made to a maximum of 94.03 percent in related systems, and direct studies of annular passages have been promising with optimized configurations. The morphological characteristics of 1D and 2D nanoparticles in the thermo-hydraulic performance are also stressed. The review ends with the determination of the most effective strategies and the description of future research in this crucial sphere of thermal engineering.