Comparative study on thermal performance of twisted tape and wire coil inserts in turbulent flow using CuO/water nanofluid

• Heat transfer and friction factor characteristics of nanofluid flowing in a tube with inserts are studied experimentally.
• Increasing nanofluid volume concentration enhances the heat transfer and friction factor.
• Further heat transfer and friction factor enhancements for nanofluid in a tube with twisted tape and wire coil inserts.
• Maximum increase in Nusselt number of 45% for 0.3% nanofluid in a tube with wire coil insert-2 under turbulent flow.
• Two empirical correlations are developed to predict Nusselt number and friction factor.

Heat transfer and friction factor analysis of CuO/water nanofluid flowing through a tube under turbulent flow conditions and with twisted tape (TT) and wire coil (WC) inserts were presented in this paper. The experimental investigations were performed in the Reynolds number range from 4000 to 20,000, volume concentrations of 0.1% and 0.3%, twisted tape inserts of h/d = 5 and 10 and wire coil inserts of p/d = 1.97 and 2.95. The experimental results indicated that under same operating conditions and flow rates, heat transfer coefficient, friction factor and thermal performance factor associated with nanofluid in a tube with wire coil inserts are higher than those with the twisted tape inserts. The Nusselt number enhancement for 0.3% nanofluid in a tube without inserts is 17.62%, 0.3% nanofluid in a tube with TT-2 is 31.88% and 0.3% nanofluid in a tube with WC-2 is 44.45% at a Reynolds number of 20,000 compared to water. Whereas, the friction factor enhancement for 0.3% nanofluid in a tube without inserts is 1.149-times, 0.3% nanofluid in a tube with TT-2 is 1.179-times and 0.3% nanofluid in a tube with WC-2 is 1.198-times at a Reynolds number of 20,000 compared to water. The thermal performance factor of 0.3% nanofluid in tube with twisted tape and wire coil inserts are 1.24 and 1.36 compared against water data respectively.