Parametric experimental synthesis of air-to-water finned-tube heat exchangers: Thermal-hydraulic trade-offs, selection frameworks, and design rules

• Fin designs boosted heat transfer efficiency by up to 39.6%. • Cross/triangular fins raised performance but Δp rose 16–28%. • IRSFT tubes gave 17.7–38.9% higher Nu with 20–30% less Δp. • Emulsion coolant raised HT 1.1–1.3 × but tripled Δp at high flows. • Flat tubes improved heat transfer by 13–18.5% over other shapes. The continuous increase in energy demand directly contributes to global warming and environmental impacts. While renewable energy remains essential, it alone cannot fully address these challenges. An additional, highly effective strategy is waste heat recovery (WHR) and hybrid systems such as ORC, SR, sCO₂, TEG, CHP, and CCHP, which are widely employed in heavy industries. Such systems experimentally enhance vehicle fuel efficiency by up to 15%, reduce industrial operational costs by as much as 80%, and improve energy recovery by 63%. Heat exchangers (HEs) are critical components in WHR, HVAC, HE networks, and HPHX systems. Among them, finned-tube heat exchangers (FTHXs) are particularly effective owing to their extended surface area and compact design. This paper provides an organized and critical synthesis of recent experimental work on the design, performance, and optimization of FTHXs. Various fin and tube configurations; cross, triangular, louvered, and perforated fins; parallel, cross-current, and countercurrent flow patterns, are systematically compared. Under optimal counterflow conditions, improved fin shapes achieved up to 39.6% higher experimental heat transfer efficiency, while cross and triangular fins exhibited 16.4–28.5% higher performance with greater flow resistance. Additionally, six key experimental setups are examined and tabulated, summarizing common testing procedures, parameters, and measurement protocols in air-to-water systems. Optimization techniques and performance enhancement strategies are highlighted. Thermal-hydraulic metrics and performance trade-offs are analyzed, also harmonized selection frameworks and design rules are proposed, supported by three case studies proving that optimized FTHX designs effectively enhance real-world thermal system efficiency in alignment with global sustainability goals.