Effect of Rectangular Winglet Pairs in Fin-Tube Heat Exchanger: An Irreversibility Analysis

The present study investigates the entropy-generation and irreversibility characteristics of air flow across a fin-and-tube heat exchanger fitted with rectangular winglet pairs (RWPs). A three-dimensional computational fluid dynamics analysis was carried out for Reynolds numbers between 2000 and 4000 and angles of attack of 15°–60°, considering RWP locations at upstream, adjacent, and downstream positions relative to the tube centerline. The total, thermal, and viscous entropy-generation rates were evaluated using second-law formulations, and exergy-based parameters such as the entropy-generation ratio (EGR), irreversibility distribution ratio, Bejan number, and thermal efficiency index were employed to assess overall performance. Results show that an upstream RWP at 30° angle of attack and Reynolds number of 3000 provides the best thermodynamic performance, reducing the total entropy-generation rate by approximately 17% (EGR = 0.83) and increasing the heat-transfer improvement number by about 18%. The Bejan number remains above 0.95 for all cases, confirming that heat-transfer-related irreversibility dominates over viscous effects. Exergy analysis further indicates that the total irreversibility decreases while the thermal improvement factor increases with optimized RWP placement. The findings offer practical guidance for the design of energy-efficient fin-tube heat exchangers using vortex generators.