Thermal-hydraulic performance and optimization for finned-tube heat exchanger in gas wall-hung boilers

Improving the efficiency of the main heat exchanger in gas wall-hung boilers is essential for energy conservation and carbon neutrality. However, limited space availability restricts heat transfer enhancement in these systems. This study firstly investigated the thermal–hydraulic performance of conventional dimple slotted finned-tube (F-D) heat exchangers, revealing that insufficient fluid mixing and serious flow dead zones reduce heat transfer efficiency. To address these issues, an airfoil four-slotted fin design with integrated vortex generators (F-A) was proposed and evaluated through both numerical simulations and experimental testing. Three prototypes were examined: F-A design with 57 fins, and two configurations of F-D (57 fins and 74 fins, labeled F-D1 and F-D2, respectively). The results showed that the F-A design improves heat transfer performance by 14.4–21.2%, yielding an overall performance coefficient (PEC) of 1.1, a significant improvement over F-D1. In contrast, the denser fin structure of F-D2 resulted in a PEC below 1.0 at high Reynolds numbers. Additionally, empirical correlations for the Nusselt number (Nu) and friction factor (f) on the flue gas side were developed. The proposed high-efficiency finned-tube heat exchanger demonstrates substantial potential in improving energy efficiency of gas wall-hung boilers.