Abstract—Convective heat transfer was experimentally investigated in tubes with helical coils inserts in tur bulent flow regime within Reynolds number range of 14400 ≤ Re ≤ 42900. The present work aims to extend the experimental data available on wire coil inserts to cover wire diameter ratio from 0.044 to 0.133 and coil pitch ratio from 1 to 5. Uniform heat flux was applied to the external surface of the tube and air was selected as fluid. The effects of Reynolds number and wire diameter and coil pitch ratios on the Nusselt number and friction factor were studied. The enhancement efficiency and performance criteria ranges are of (46.9– 82.6%) and (100.1–128%) within the investigated range of the different parameters, respectively. Correla tions are obtained for the average Nusselt number and friction factor utilizing the present measurements within the investigated range of geometrical parameters and Re.