Experimental and numerical investigation of swirling turbulent flow and heat transfer due to insertion of twisted tapes of new models in a heated tube

•Effects of new models of tapered twisted tape are investigated.•Thermal performance factor is obtained experimentally and numerically.•Starting width and length of the tapered region affect differently.•A proper starting width and tapered region length give better performance factor. In this work, the effects of new tapered configurations of twisted tape on thermal and hydrodynamic fields in a heated tube were studied experimentally and numerically to determine the best configuration that provides the highest thermal performance factor. The tube surface was under constant heat flux and air was chosen as the working fluid, with a turbulent flow of 10,000 ≤ Re ≤ 40,000. The RNG k-ε turbulent model was used in the numerical part. For the first time, the tapered region was varied in its length (l) and starting width (SW), which represents the novelty of this work. The maximum increase recorded in the experimental and numerical results was 75% and 100% respectively for the Nusselt number, and 220% and 226% respectively for the friction factor. Similarly, the maximum experimental and numerical thermal performance factor was 1.19 and 1.37, respectively. Subsequently, the experimental data obtained for the Nusselt number, friction factor, and thermal performance factor were described using empirical correlations.