Enhancing thermal performance of evacuated tube solar collectors through integrated turbulators, expanded copper mesh, and hot-cold water separation

This study investigates the thermal and economic performance of Renovated Evacuated Tube Collectors (RETCs) enhanced with passive components. The RETC configuration integrates a helical turbulator, expanded copper mesh, and a concentric hot–cold water separation pipe to improve convective heat transfer, conduction, and thermal stratification. A fixed parabolic reflector with a concentration ratio (CR) of 4 was also employed to increase solar irradiance on the absorber surface. Experiments were conducted in Erbil, Iraq, under real climatic conditions to compare the RETC with Conventional Evacuated Tube Collectors (CETCs) across various configurations during January to May. Results demonstrated that the RETC consistently outperformed the CETC across all tested mass flow rates (0.01–0.03 kg/s), achieving a peak thermal efficiency of 77.3% and a maximum outlet temperature of 83.0 °C. Performance enhancements were primarily attributed to turbulence induced by the turbulator, the increased surface-area-to-volume ratio of the copper mesh, and reduced mixing losses due to the separation pipe. Statistical validation using error bars from five repeated trials confirmed the reproducibility of the results. Economic analysis revealed annual savings of approximately 387 USD with a simple payback period of 1.29 years. These findings establish RETCs as technically reliable and economically feasible for residential water heating in semi-arid climates. • RETCs with turbulators, copper mesh, separated pipes, and reflector tested. • RETCs achieve 77.3% peak efficiency, surpassing CETCs by 12.08%. • Maximum outlet temp of 83.0°C with 180 cm turbulator in RETCs. • Longer turbulators (120-180 cm) boost thermal performance.