Heat Transfer Enhancement in a Concentric Tube Heat Exchanger Using Dual‐Side Helical Wire Coil Inserts: A Numerical Study With Experimental Validation

ABSTRACT Heat exchangers are extensively used in chemical processing, power generation, food processing, HVAC systems, and energy recovery applications, where improving thermal performance without major equipment modification is highly desirable. This study investigates the use of helical wire coil inserts as a passive enhancement technique for improving the performance of a concentric tube heat exchanger operating under turbulent flow conditions. Three configurations were analyzed: a smooth heat exchanger, a heat exchanger fitted with an inner‐tube coil, and a dual‐enhanced configuration incorporating helical wire coils on both the tube side and annulus side. The coil geometries were obtained by scaling the optimum dimensionless ratios ( e / D = 0.036 and p / D = 0.86) reported in previous single‐tube investigations, resulting in a 0.5 mm wire diameter with 12 mm pitch for the 14 mm inner tube and a 1.0 mm wire diameter with 24 mm pitch for the annulus. A three‐dimensional CFD model was developed and validated against experimental data obtained from the smooth heat exchanger, with outlet temperature deviations below 0.1%. Simulations were performed at Reynolds numbers of approximately 5000, 5500, and 6000. The inner‐tube coil increased the hot‐side Nusselt number by 31%–32% and heat exchanger effectiveness by 26%–27% compared with the smooth configuration. When an additional annulus‐side coil was introduced, the hot‐side and cold‐side Nusselt numbers increased by 40%–41% and 41%–43%, respectively, while effectiveness improved by 33%–34%. The annulus‐side thermo‐hydraulic performance factor remained above unity (1.19–1.65), indicating a favorable balance between heat transfer (HT) enhancement and pressure drop penalty. The results demonstrate that dual‐side wire coil enhancement provides significant thermal performance improvement and can be adopted as a practical retrofit solution for industrial heat exchangers requiring increased heat recovery, reduced equipment size, and improved energy efficiency without major structural modification.