Comparative heat transfer analysis of helical coil and straight tube heat exchangers

This study presents a comparative analysis of heat transfer and hydraulic performance in helical coil and straight tube heat exchangers using computational fluid dynamics (CFD) simulations and experimental measurements. Both exchangers were fabricated from seamless copper tubes with identical inner diameters (10 mm) and tested under matched conditions with water as the working fluid. Experiments covered mass flow rates from 0.0315 to 0.3154 kg/s, corresponding to Reynolds numbers between 1068 and 12685. CFD simulations were performed using ANSYS Fluent, employing a validated mesh, suitable turbulence models, and boundary conditions that replicated the laboratory setup. Results show that the helical coil consistently achieved Nusselt numbers 8–12 % higher than those of the straight tube and greater water outlet temperature reductions across all tested regimes. However, this improvement was accompanied by a moderate increase in pressure drop of up to 20 %. CFD predictions agreed well with experimental results, with deviations in Nusselt number and outlet temperature within ±9 %. The relative uncertainty in the heat-transfer rate ranged from about 12 % at the lowest flow rate, where the temperature rise across the exchanger was small, to roughly 5 % at the highest flow rate. The study provides practical performance evaluation criteria for design engineers, emphasizing the balance between heat transfer enhancement and the pumping power required. Future work should investigate multi-phase flow and long-term operational stability to extend industrial applicability.